Learning about Dried Flowers
 

Drying Flowers
Air Drying    Dehydrator    Glycerin    Burying    Microwave    Pressing

Flowers or leaves for drying may be collected at any time during the growing season from early spring until late fall. Always collect more material than is needed, to allow for damage. Use only the most perfect forms. Poor shapes dry as poor shapes. Use only plants and flowers free of insect and disease. Damage becomes only more obvious after drying. Pick flowers when they are free of dew or rain, preferably in the late afternoon. Place stems promptly in a container of water to prevent wilting while gathering.
Do not be afraid to collect items with interesting curvature (Sticks, grasses, etc) ....they could prove to be an interesting part of the arrangement.
In addition to flowers, stems and leaves that may be dried indoors, there are many materials that can be collected in the autumn/fall and used almost directly in arrangements after gathering.
 These include many seed pods, cones, grain, grasses and berries found in the garden as well as in fields and roadsides.        (start of page)
Methods for drying flowers
Air drying.

 There are a number of garden flowers, as well as wild plants, that can be dried simply by hanging them upside down in a warm, dry place for several weeks. Flowers best suited to this are the "everlastings" and a few others that do not wilt readily. Some, such as globe amaranth, can be dried in bunches on their natural stems. Others, such as strawflower, should have a wire substituted for stems before drying.

Steps for air drying
Cut flowers of good quality, sometimes it is better to use very mature flowers, when they are fully open, and well into the open cycle.
Remove foliage from stems. If stems are weak or become brittle after drying, remove them and wire the flowers.
Group the stems into small bunches and tie with a rubber band. It will pull tighter as the stems shrink during drying.
Hang upside down in a warm, dry, dark area such as an attic, dark garage, etc. Avoid damp rooms or direct sun on the flowers. Good air circulation is important.
Allow to remain until thoroughly dried. This normally takes two to three weeks.

Natural stems dried in this process will generally be fairly straight. These may be bent for arranging by submerging the stems in warm water until they have softened. Then, bend them to the desired position and weight them in that position until they have dried. You can also use wire to achieve the desired shape.

Some Flowers that are suitable for air drying.-There are many others not listed here.  

Using Dehydrator Machines

These machines are quite popular these days, and can be bought quite cheaply from many stores.
They work along the principle that warm air is directed upwards and sideways along a stack of trays, where heads of flowers can be laid ...head up or horizontal, as well as the bunches can be held by wire, dangling down, and moving some of the separators accordingly. The temperature and time can be set to any  level.
This system is best used for flowers that are difficult to dry by the air method...example...Roses-Gardenias-Stephanotis-and many others.

Freeze Dried Machines are also available, and although they can do a better job than the Dehydrator, they are far more elaborate and expensive. Furthermore, a number of people reported re absorption of moisture in time.

Glycerin 

Glycerin is an alcohol, that is a clear, colourles, odourles, viscous liquid when pure, and has a warm, sweet taste with a high boiling point It is a product of  the petroleum industry, and  the chemical and physical properties possessed by Glycerin has resulted in its wide range of uses. 

This  includes the food and beverage industry, medicine, cosmetics, emulsifiers, resins, cellophane and paper, explosives, tobacco, textiles, glue and gelatin, photography, leather, antifreeze, lubricants, rubber, cork composition, adhesives and cements, agriculture, glass, cleaning agents, electrical equipment and metals.  In the flora preserving industry, it has the unique power of not evaporating, which means once it is absorbed into the veins of the leaves, it will remain there and leave them pliable. 

However, one must remember that if you glycerine a stem of say, Eucalyptus, it can remain wet if the stem is kept in a closed environment, without enough air circulation. To the chemically minded, the formula for glycerin is HOCH2CH(OH)CH2OH.

Preserving foliage with Glycerin       

The dried flower arrangement without foliage may seem stiff and unnatural. Leaves add much to an arrangement and can easily be preserved by a process known as "glycerinizing." This technique makes the leaves and stems soft, pliable and long lasting so they may be used over and over.
Select branches with the desired curves and with foliage that is not damaged by insects or disease. In general, a branch about 18 inches or less in length is best for glycerinizing.

Remove lower leaves, and crush or split the stem end of wood materials to increase absorption.
Make a mixture of one part glycerin and two parts warm water. Stir well and pour into containers so the liquid is about 4 to 5 inches deep.
Mark the level of the mixture on the container (glass containers are best) and place the stem end of branches into it.
As the branches absorb the mixture, add a reserve mixture which contains one part glycerin to four parts water to the original marked level.
Foliage color will gradually change as the glycerin is absorbed. It will take from one to three weeks for most branches to glycerinize.
Some leaves, especially thick and waxy ones, may not glycerinize well by this method. Individual leaves of plants such as ivy or southern magnolia may be glycerinized by totally submerging the leaves into the mixture. They should be placed in a single layer and weighted to keep them beneath the liquid. After they become soft and pliable (2 to 6 days) they should be removed. After removal, drain and wipe the leaves clean with a soft cloth.
It is difficult to say which leaves are best suited for glycerinizing, as sap conditions change from leaf to leaf...the best system is one of experimentation in your local conditions.

Some flowers respond to a mixture of glycerine and air drying....Hydrangeas for example- these can be difficult to dry successfully, the most important step being to cut them at the right time, invariably just when the flower finished its flowering cycle, and just when it begins to fade. Let the stem stand in a glycerine/water solution for a week (2 inches) then hang upside down till it dries....alternatively just let it stand in three inches of water, till it absorbs the mixture, then it can be hung upside down, or sometimes it dries perfectly standing the right way up, with perhaps some support for the head.
To read a full article on the use of Glycerine refer below.

Pressing flowers

Pressed flowers are especially suitable for flower pictures, as well as decoration on note paper, place cards and many other items.
To collect flowers for pressing, use flowers with different stages of development up to full maturity for more variety in design. Avoid plants with fleshy stems and leaves as well as flowers with very thin petals. Don't try to press wilted materials. Flowers that are flat, such as pansies,leaves, etc press best.
The faster flowers dry, the better they retain color. On the other hand, flowers can't be exposed to excessively high temperatures. Although they may dry quickly, they will turn brown.
Pressing requires sandwiching flowers and foliage between layers of an absorbent material. This should be clean and hold the flowers firmly and flat during the drying process. Porous materials that allow some air movement are also beneficial.

Flowers are generally placed between a non-glossy type of paper. Newspapers, old telephone directories or catalogs are suitable. Absorbent facial tissues placed on the pages aid rapid moisture absorption. Tissues should be removed and flowers or foliage replaced between fresh, dry tissues and papers at the end of the first week. After the flowers and tissues have been placed in the folded newspapers or books, stack them several layers deep. Place boards beneath and on top of the stack. Put the stack in a warm, dry place with a heavy weight on top.
Another very satisfactory system suitable for drying flowers uses a combination of cardboard, newspaper and desk-sized blotter pads. Corrugated cardboard is cut into sheets slightly larger than the sheets of folded newspaper. Flowers are positioned on one side of the opened newspaper. Then the newspaper is closed and a sheet of blotter paper placed on either side.

After all flowers have been placed between the newspapers, blotter paper and cardboard, the layers are stacked and tied or taped together. They should then be placed in a warm, well-ventilated place and weighted. If large numbers of flowers are pressed, write a date on the stacks to keep track of drying time. Special presses can be purchased or constructed for drying large quantities of materials.
The flowers listed in Table 2 produce good results when pressed. However, there are many others that may be used, and experimentation with those available is suggested.
                                                                                               

Drying mixtures for burying flowers

Flowers may be dried in their natural form by totally burying the flowers in one of several materials.
Borax combined with sand or corn meal. One of the least expensive mixes for drying flowers is made from sand and borax. The sand must be fine, clean and dry. Sand is relatively heavy to work with and tends to flatten flowers unless used very carefully.

A more popular mixture for drying is made of equal parts of borax and white cornmeal. The cornmeal is light weight and has less tendency to flatten flowers. It also makes boxes easier to handle and move after filling. The main function of these materials is to hold the petals in place while they dry naturally. Good aeration is important for rapid drying. Some people feel that the addition of about three tablespoons of non-iodized salt per quart of mix helps petals retain color during drying. The ratio of borax to sand or cornmeal varies widely, but the quality of drying does not seem to differ greatly between them. Ratios varying from 1:1 to 1:6 have been used (first number refers to borax).

Silica gel. In general, the most satisfactory material for drying flowers at home is silica gel. Initial cost is greater than that of borax-sand or borax-cornmeal combinations, but it can be used over and over for many years. Since it dries flowers quickly, more flowers can be moved in and out of the mixture during a single season than in the same quantity of a borax mixture.
Silica gel is available under a number of trade names. It is white, but some types contain blue crystals that act as an indicator of the amount of moisture which has been absorbed. When these crystals are a clear blue the material is dry. As the moisture is absorbed from the flowers, the crystals gradually turn pink. At that point it is time to re dry before using again.
To dry the material, spread the silica gel on open pans or cookie sheets in a layer 1/2 to 3/4 inch thick. Bake in an oven at about 250 degrees until the crystals are blue again. This may take about an hour. Stir the crystals several times while they are drying. Keep unused silica gel in air-tight containers.
Burying flowers for drying

The method for burying flowers in any of these materials is essentially the same. However, there are some differences in the types of containers to use, as well as drying with either natural stems or wire stems.
Containers. Flowers dried in borax mixtures should be left uncovered during the drying process. Therefore, low cardboard boxes with tight, strong bottoms are ideal. This allows good air movement throughout the mixture, and if desired, stems may be left attached and sticking out of the mix to air dry.
Flowers dried in silica gel must be placed in air-tight containers. If the containers are not sealed tightly, the silica gel absorbs moisture from the air, and flowers dry too slowly or not at all. Candy tins, plastic containers, coffee cans, large-mouth jars, or any other container with a tight fitting lid may be used. If nothing with a tight lid is available, seal loose tops with tape.
Use shallow containers to make maximum use of the drying material. The natural stem should be removed before drying most flowers in silica gel. Therefore, flowers wired before drying are more easily arranged later.

Wiring. Two techniques of wiring may be used — hook wiring and cross wiring. Hook wiring may be used for daisies, marigolds, zinnias, or other flowers with soft centers. Flowers with a harder base or center, such as roses, should be cross wired .To hook wire a flower, use about a 20 to 24 gauge wire and push it upward through the center of the stem, if hollow, or through about the center of the flower. Push it out the top of the flower, bend a small hook in the end of the wire and pull it back into the flower, hooking the center. Make sure that the small hook is well hidden in the flower's center. If it is not, as the flower dries, it will become visible. To cross wire a flower, push the wire through the base of the flower at right angles to the stem. The wire is centered in the flower base, and both ends are then bent down to form a short stem.
In shallow containers, the wires may be bent several times or simply bent out of the way for drying. Later, they can be straightened after the flowers have dried and other wires added to prepare them for arranging.
As most of these flowers dry, colors will darken. Therefore, extremely dark flowers, especially in the red, purple and blue ranges, may become almost black after drying. Whites generally develop a cream or tan color.

Burying the flowers. Flowers with wired stems are dried facing upward, and the stems are bent or curled to lie parallel to the bottom and out of the way. Flowers on natural stems may be dried on their sides (as in the case of spike flowers such as larkspur or snapdragon) or upside down with stems protruding upward. Working the drying agent between the petals is difficult when flowers are placed facing downward. When placing flowers on the side, a brace is necessary to hold the stems so flowers on one side are not flattened.
To dry flowers facing upward:
Place a layer of drying material in the bottom of the container about 1 to 2 inches deep.
Bend the wire stems to the side or curl up.
Place the flower on the layer of material in the bottom of the container. Push wire stem down into material.
Gently work the base of the flower into the material so it is well situated, petals supported and in a normal position.
Gently sift the material over the petals, making sure that all petals remain in place as the material is added.
If any petals are bent, use a toothpick or similar item to reposition them.
Continue to add material until each flower is entirely covered.
After all flowers have been added and covered, lift the container and tap it gently on the base to help settle the material.
After tapping, make sure all petals are still covered. If any have been exposed, add more drying material.

Prepare for storage.
Borax combinations can be placed directly in a warm dry place without covering. Drying will normally take two to three weeks.
Silica gel should be tightly covered or sealed if the lid is not air tight. Flowers should dry in three to eight days. The exact time varies with the thickness of the flower. If removed too soon, petals will droop. If removed too late, petals become brittle and break easily.
Removing flowers from the mixtures. Since petals become fairly brittle after drying, care is important when removing flowers from the mixture. Pour off or gently brush to one side some of the mixture on the surface of the container. As petals become visible, gently lift the flowers upward by placing the fingers beneath them. Turn each flower upside down after removal and tap out any remaining residue. If a white dust remains, remove it by carefully brushing with a soft, dry artist's brush or gentle stream of air.
Some flowers, such as chrysanthemum, drop petals easily. These can be reinforced by dropping glue on the bottom at the base of the petals. Use a glue that becomes clear after drying.
Adding stems for arranging. Flowers often need wire in the stem for arranging. A heavier wire, such as 18 gauge, may be used. Simply twist the short wire that was placed in the flower around the stem-wire and wrap them together with floral tape.
                                                                            
                                                                                                    

Microwave oven drying

Microwave drying takes only a few minutes and provides dried flowers that look fresher and more colorful than those obtained by other methods. Support material such as silica gel must surround and support the flowers during heating and drying. Use heat-tolerant glass or microwave containers. Do not cover the containers. Place a cup of water in the oven before starting to help prevent excessive drying.
Drying times vary from about 3 minutes for very dense flowers with a lot of petals to about 1 minute for smaller or thinner-petaled flowers. Since ovens and flowers vary, experimentation will be required.

After treatment is complete, leave flowers in the silica gel for 12 to 24 hours to make sure they are cooled and dried. Since microwave-dried flowers tend to absorb air moisture, spray the petals with hair spray or lacquer. For long term storage, keep them in an airtight container.
                                                                                                       

Focal Flowers.

When selecting flowers for an arrangement, a good rule of thumb is to select three or four different bunches. Establish the perimeters for your bouquet with line flowers, such as eucalyptus, bunny tail, straw or wheat. The focal flower should be something interesting that draws the eye - straw flowers or dried seed pods. Filler flowers, such as statice or baby’s breath, will round out the arrangement.Your bouquet should coordinate in terms of color, texture and shape. Keep in mind the décor of your home, where you plan to place the arrangement and the mood you want to establish. Floral arrangements constructed of yellow and red tones help to foster a warm feeling in a room. Blues and greens create a cooler feeling.

Monochromatic arrangements, which use tints, tones and shades from the same color family, make for a very interesting visual effect. An example would be a bundle made up of red, pink and burgundy flowers. Strongly contrasting colors, like red and blue, also have a lot of impact. A third design option is to use complimentary colors such as blues and greens. 

To tone down a brightly colored arrangement, add some hues of brown and green. Jazz up a bouquet with a splash of red and yellow. Experiment with various textures (like seed pods) and shapes to modify the look of your arrangement. There are many varieties of textures available.
                                                                                               

Line Flowers

The outline of the design is marked by using line flowers.
This could be in the form of foliages, like gum or other grasses, or any stem or multiples of flowers that are smallish in diameter. The need for this parameter, is that the eye need to perceive Balance in your design, not side or top heavy...there is a built in sense of proportion in our visual mechanics.....The heavy have to support the light.
                                                                                 
                                                                                         

Colour

At the outset, it has to be stated that no matter what laws relate to this important subject, colour is in the eye of the beholder, what pleases one, displeases another and viceversa. 
Another basic rule is that colour is subjective not objective, meaning that whether one line of shades is right or not, depends largely as to what is with it, in the same room. 

Finally, since a strong colour in dry arrangements comes from an artificial source, some people have a fanatical view that they prefer things natural....provided they realise that the downside of that, is that natural colour in flora fades dramatically once it is cut from its source, and browning is often the  course with some exceptions. Of course, most flowers simply fade gradually within their own colour spectrum.
The application of colour to flora comes mainly from dyes, the items are simply inserted in solutions, made from the dye and water mixtures and then allowed to dry. Most dyes in todays world come from artificial processing with some minor exceptions. Spray cans offer a simpler solution, and if the quantity of flora to be coloured is small, it is by far the cheapest method of doing this. You have to make sure to only spray in well ventilated areas, and protect yourself from any possible harmful fumes by wearing a mask, and gloves. 

After Care

Dried flowers are delicate. Although new manufacturing processes have made them softer and last longer, here are a few hints that will make your arrangements last twice as long. Arrangements can last for up to 10 years, though most professionals predict three to five. By that time, the piece may start to look ragged and some or all of it will need to be replaced.

Dried flowers treated with a matte or gloss clear acrylic sealer will last just a little bit longer. You can also spray any type of dried flowers with a colored acrylic spray. One coat provides a nice, light color; two produces a deeper tone. Moss, which tends to dry and lose its color, is a good candidate for this method. An acrylic spray will maintain color forever. 

When flowers are dried, obviously their moisture has been removed. Spraying your flowers from time to time with a mister replenishes some of that lost moisture. Certain flowers, such as baby’s breath or statice, should be soaked in warm water for three to five minutes before you make your arrangement. This trick loosens and opens the flowers, making them softer and easier to arrange. Dried flowers continue to dry out quite significantly. If this happens, give them a nice steam bath. Run a shower with the door closed. After steam has collected, shut off the shower and let them sit in the enclosed room for an hour or so. This kind of refurbishes them and will make them last twice as long. 

Keep your dried flowers out of direct sunlight, which will fade the flowers and make them dry much quicker. Dried arrangements thrive in a household where the average temperature is 75 degrees most of the year. If you do notice some drying, just mist them a little bit.of water. Dried materials in storage may occasionally be attacked by one or more household insects such as museum beetles, silverfish, roaches or others closely related to them. As they chew on the soft tissue of the plant centers, flowers may shatter and fall apart. They are not necessarily on the flowers as they come from the garden but move into the boxes in the home during storage.

Occasionally check boxes, and if insects are present, destroy the infected materials. Tightly sealed containers prevent invasion. If the pests are present, thoroughly clean the container before using it again. Naphthalene flakes may repel insects or some general insecticides may help control them, but once an area is infested, complete eradication is difficult. Cleanliness and persistence are the best means of remedying the situation.
Don't consider dried flowers as everlasting. Preferably, they should be replaced yearly, but with good care they often last longer. Even the best dried flowers gradually fade and should be discarded when they no longer produce the desired effect. Flowers that tend to fade may be lightly tinted with aerosol paints or dyes for more durable color. With care, the natural look is preserved.
                                                                                                 

Containers

The choice of container is a very important dimension in the art of flower arranging
As a rule of thumb, the arrangement  should 
never be higher than three times the height of the container.

 Think about your home décor, flower selection, desired effect and where you plan to place the arrangement. For instance, a tall container would not look particularly good in the center of your dining room table but it might be perfect for the hallway.
In general, use a neutral container - the flowers should be the focal point, not what’s holding them. Of course, sometimes the style of container actually complements the flower arrangement, like using a delicate antique vase with a classic 

Victorian arrangement of roses and baby’s breath. A selection of this kind would not look as nice in a big, heavy basket. The flowers should suit the container chosen. 
Since water is not required, baskets are wonderful for holding dried flowers. There are all kinds of interesting  baskets available. 
Dont be afraid to use something that is totally unusual like the picture on left....or a jam jar that you just finished or a bright red tin that was used to hold crushed tomatoes, or whatever other container that triggers your imagination.
                                                                                            
 Tools

wire cutters    scissors    2½ - 3" wood picks    a spray mister    a glue gun    18-gauge stem wire    florist tape

foam    a container    optional clear acrylic sealer or spray paint Preparation

Preparation
                                               

This entails assembling together all the materials that you need for your arrangement.

Remember that you can also use artificial flowers, ie, silk, cotton, etc...this choice is entirely yours. Some people say that they like to keep to natural materials, hence only use dried natural flowers and foliages....others see that their arrangement is greatly enhanced by including silk flowers...
Cut the Styrofoam to size (level with the container - not above or below it). Using a glue gun, apply glue to the bottom of the foam and insert into the container. The foam should fit snugly. Next, take some sheet moss, pull it apart and work it tightly around the foam block.

 The moss does not need to be glued or held in place - the stems of the flowers will join it to the foam. Leave the top of the foam uncovered so that delicate stems can be inserted without having to be wired or taped. You can always fill in more moss later.

Starting
                                                   

Remember these three tips for making flower arrangements:
1. Insert flowers (except for the centerpiece) at an angle into the foam. 
2. Cut wires or picks at an angle for easy insertion.
3. Tape all wires down to their ends.

Push right into the surface and remain held in place without the need of any supportive materials 
If you plan to use a delicate flower in your arrangement, you will need to provide some support for the stem. Cut a piece of 18-gauge wire to size and lay it a little below the base of the flower (leaving a portion of the stem clear). Take the floral tape and pull it between your fingers to release the glue. Floral tape will stick only to itself. Wrap the tape several times around the top of the wire and stem. Twist the flower as you pull the tape down the stem at an angle. The tighter the turn, the tighter the tape. Wrap the flower all the way down to the bottom of the wire and insert in foam.

A wood pick with an attached wire works great for securing little bunches of flowers. Layer and stagger the flowers just a little bit. Place the wood pick close to the bottom of the flower stems. Wrap the wire round and round until the stems are truly attached to the wood stick. If that wrapped area will be visible in the arrangement, tape it quickly with floral tape. In addition to hiding the wires, this step will strengthen the bond. 
                                                                                        

Shaping    
What shape of arrangement do you have in mind in the first place?

You need to be very clear as exactly what you are trying to achieve....if necessary draw your shape outline on a piece of paper....A graph paper, where you can draw your arrangement to scale can be helpful, until you become proficient enough not to need this...Establish exactly how big you want it to be, and make your scale model accordingly..from the center, draw lines out to scale, and at the right angle..

So lets assume that you are making a facing arrangement, say an A shape....  First, set your lines for the arrangement. insert one flower or leaf stem  straight into the center of the foam block. Imagining the surface of your foam block is a clock face, insert another flower (at an angle) at 12, 1, 2, 3,and perhaps 4 o’clock..remember that the length of the stems should be graduated such, that a string will just touch the end bits, if it were to be stretched from vertical to 3 o'clock Repeat the same on the other side, ie 12 to 9....

 Emphasize these lines by inserting focal flowers, at different angles but never passing the outline of your basic triangular shape. A helpful hint in design here is that fine pointed foliage and flowers (Line flowers) are always put towards the end, while larger flowers (focal) are always towards the center.... Balance is an important consideration.The arrangement must always look and act that it will not topple over, does not look that it is leaning to the front or the back, or any one side. Basically, large flowers are always put quite central and down. You have to train your eye, to focus on what constitutes Balance, and in reality what is pleasing to one's eye. 

The drawing on the left, gives an outline of a table center piece as viewed from the top. looking down on the arrangement....in this case, the horizontal line is longer than the width, as would be suitable for example in a rectangular coffee table .The main feature of such a design, however, is that it has to look nice from all angles, hence this is an all round design. The other feature to note is that the center point is the highest and then it graduates down to container level.

Accessories

It need not be assumed that all the items in a design have to consist solely of flowers and foliages...
Things that can be incorporated are....Dried Fruit in slices, artificial fruit, vegetables, or indeed any material that is dried and lasting.

Bows made of a variety of ribbon material can be incorporated,

 giving an effect that you, the designer find pleasant to look at. 

Ribbons made of more rustic material seem to compliment the looks of dried flowers better than that made of silky or other 

shiny material. Use wire to hold the ribbon loops together, then use the flora tape to cover the wire.

if you like using a mixture of artificial and dried flowers, by all means do so. In most cases this will enhance greatly the final look, and certainly the strong colour of  your design.

Making your own PotPouri??

There are many ways that one can make this...it all depends on the aroma of your choice...

The sense of smell is as varied to humankind as ever.

General guidelines are....

Obtain leaves and herbs of your choice
A glass jar or decorative container
Mineral safflour oil or similar
Scented oil or perfume
Spices 
Peppers
Directions:

Place dried flowers, leaves and herbs into a decorative bottle or glass jar.

Gently pour oil into bottle over dried material and herbs.

Add 3-4 drops of perfume, cologne or scented oil of your choice.

Place lid onto container. Shake gently to mix oil and scent together.

You may also choose to remove the lid in certain areas, like the bathroom, so that the aroma can fill the room.

Now, if you want to use the oil, place whole peppers and herbs into glass container and mix with oil. You can also mix in a pinch of your favorite seasons such as dried peppers whole, thyme, ginger, cinnamon sticks,etc.

When liquid is running low, just add more oil.

You can also paint designs on your jar or vase if desired.

Be sure to cap tightly.

Preserving with Glycerine
published by courtesy of  Paul Dubois, Research Officer, Division of Horticulture, South Perth and Dr Daryl Joyce, Horticultural Science Department, Murdoch University (Australia)

Glycerining is the term used in the ornamental cut flower and foliage processing industry to describe the treatment of fresh plant material with a hygroscopic (water attracting) chemical with the objective of retaining the suppleness of the plant material.

Glycerine (glycerol) is most widely used for this purpose although many chemicals possess hygroscopic properties. Cellulose, the major constituent of the plant 'skeleton' is brittle when dry. Adding a hygroscopic chemical (humectant) prevents cellulose from drying out completely, which keeps the plant material supple.

About 50 per cent of most plant fresh weight is water, but brittleness is usually only a problem if the water content falls below 10 per cent.

Suitable chemicals

Hygroscopic chemicals suitable for use as humectants for ornamental foliage can be grouped into four classes: polyols (glycerol, glycols); sugars (sorbitol, sucrose); salts (CaCl₂, NACI) and quaternary ammonium compounds.

Glycerol is the most efficient humectant because it has the greatest water attracting capacity (see Table 1). Diethylene glycol and the polyethylene glycols have been used as humectants for ornamental foliage. However, their lower water holding capacity means that a greater quantity is needed for a given degree of suppleness.

Polyethylene glycols are available in a wide range of different molecular weights. Those of interest as humectants have molecular weights ranging from 200 to 1,000. As a general rule, the water holding capacity of glycols decreases as molecular weight increases. Ethylene glycol and propylene glycol are hygroscopic, but are too volatile to be used as humectants for ornamental plant material.

Sugars are used as humectants in foods. Sorbitol has approximately half the water holding capacity of glycerol and has potential as an alternative to glycerol because it is cheaper.

Salts are even cheaper, but are only suitable for use in high humidity environments because most salts fail to attract sufficient moisture below 50 per cent relative humidity (RH) to prevent foliage from becoming brittle. Calcium chloride (CaCl₂) and magnesium chloride (MgCl₂) are the most efficient humectant salts; sodium chloride (NACl) is less efficient. Unfortunately, calcium salts cannot be applied to plant foliage by stem absorption, but they are suitable for application by soaking (for example after bleaching).

Quaternary ammonium compounds (for example, Comfort®) also have potential as humectants for plant foliage in this manner.

Both the humectant (if liquid) and the water it holds will contribute to the suppleness of treated foliage.

Water holding capacity

The water holding capacity of a humectant varies according to atmospheric humidity. Figure 1 illustrates how the water holding capacity of glycerol varies with humidity. It can be seen that the water content of glycerined foliage will not vary appreciably when the atmospheric humidity is below 80% (usually the case in Australia). In this case, because the humectant can attract only a small quantity of water (say 20 to 40 g water per 100 g of glycerol), a substantial quantity of humectant is required to make dried foliage supple - see Table 1.

Table 1. Comparison of the water holding capacity of selected humectants at several relative humidities (RH)

 

	Water holding capacity (g/100 g of humectant)
Humectant	30% RH	60% RH	90% RH
Propylene glycol	10	40	270
Ethylene glycol	13	37	180
1,3 Butylene glycerol	10	30	205
Dipropylene glycol	6	18	96
Diethylene glycol	9	23	115
Triethylene glycol	7	22	100
Glycerol (glycerine)	12	41	215
Sorbitol	2	30	135
Polyethelene glycol 400	6	26	127
Polyethylene glycol 600	4	20	90
Sodium chloride	15	15	950

At high humidities, all humectants absorb a great deal of water from the atmosphere, and so proportionally less humectant is required to keep foliage supple. At 90 per cent relative humidity, glycerol will have a water content of 215 g per 100 g of glycerol.

Therefore, to maintain suppleness in a 90 per cent relative humidity (RH) environment will require only about one-fifth the amount of glycerol that is required in a 60 per cent environment. Water holding capacity of humectants varies greatly at high humidity and this causes the problem of sweating under such conditions.

Applying humectants

Humectants can be absorbed into plant tissue either by transpiration stream uptake or by immersing the cut foliage in a humectant solution.

Immersion method

Immersion is the less convenient method, requiring large vats, substantial quantities of humectants, and time. Depending upon species and market, the treatment is by immersion in a solution of 10 per cent to 50 per cent humectant volume for volume (v/v) for one day to three weeks. Generally, immersion is used only when the stem uptake method is impractical (for example when dealing with bleached foliage). Calcium chloride (CaCl₂) is the cheapest humectant for the immersion method. Quaternary ammonium compounds (for example, Comfort®) are popular, and result in a more supple product than does calcium chloride.

After immersion, the foliage is lightly rinsed in water to remove sticky surface residue, and is then hung to dry.

Stem uptake method

Applying the humectant by stem uptake is the preferred method for convenience, as all that is required is an airy room and buckets of humectant solution to stand the plant material in. It is advisable to ensure that leafy foliage is not too tightly bunched or crowded in the bucket.

Overcrowding will interfere with air circulation through the foliage. Free air circulation is necessary for uniform absorption of the preservative solution into all parts of the, foliage. If possible, cut the bunch ties, then rebunch after uptake has ceased. The use of fans to create air movement can be beneficial.

Plant material destined for glycerining by stem uptake must receive careful post harvest handling because uptake relies on a living process (transpiration).

• During handling and transport, keep the plant material cool and out of direct sunlight to avoid desiccation and death of the foliage.
• Minimise the time of dry handling, or the ability of the plant material to take up the humectant solution may be impaired.
• Use only foliage consisting of full sized leaves. Avoid young, sappy foliage as it usually wilts during the uptake process.
• Trim the stems by 1 to 2 cm immediately before placing them into the uptake solution, to ensure that gums do not prevent solution uptake.

There is no evidence that practices such as slitting or fraying the stems increases uptake, and in some cases they have been shown to reduce uptake.

Absorption

Absorption can be continued around the clock (if temperature and humidity levels are suitable) by providing a continuous low level of illumination which will allow stomata on the leaves; to remain open. It should be noted that night time humidity is normally higher than day time humidity and so absorption at night will be slower.

The concentration of the glycerol in the uptake, solution will increase over time, because water will evaporate at a faster rate than the humectant. Where a solution is to be reused many times, the concentration may easily be monitored by checking its specific gravity or refractive index. Use either a hygrometer or refractometer, such as is used for monitoring sugar levels in fruit.

Temperature and humidity

The rate of uptake of a humectant is dependent upon the rate at which the stem transpires (that is loses water by evaporation from the leaf surface). Low temperatures greatly reduce the rate of transpiration and make glycerining slow. High humidity also reduces the rate of transpiration. These factors are interrelated, and can be described in terms of the vapour pressure deficit (VPD) that exists between the leaf surface and the atmosphere.

The larger the vapour pressure deficit (within reason), the greater the rate of transpiration. VPD can be estimated with the accompanying chart (Table 2, below). Knowing the humidity (easily measured by wet bulb temperature depression) and temperature, a quick calculation will reveal whether glycerining under such conditions is possible (that is the VPD is positive). If not, the humectant solution can be heated to increase the VPD. Experiments have shown that an acceptable rate of glycerining occurs if the VPD is greater than 10 millibars. (See the working example below Table 2.)

Table 2. Chart for the determination of water vapour pressure (in millibars)

 

	Relative humidity (%)
Temper- ature (ºC)	10	20	30	40	50	60	70	80	90	100
10	1	2	3	5	6	8	9	10	11	12
15	2	3	5	7	9	10	12	13	16	17
20	2	4	7	8	11	13	16	19	21	23
25	33	7	10	13	16	19	22	26	29	32
30	4	8	12	17	21	25	29	34	38	42
35	5	11	17	22	28	34	39	45	50	56
40	8	15	22	30	37	44	52	59	67	74
45	10	19	29	38	48	57	67	77	86	96
50	12	25	37	49	62	74	86	99	111	123
55	16	32	47	63	79	95	110	126	142	158

A working example

A preserving solution will only be taken up by plant foliage if the correct environmental conditions are provided. The VPD must be positive and should be as high as possible (preferably greater than 10 millibars) for rapid preserving. VPD can be established from Table 2 if ambient temperature and relative humidity are measured. Relative humidity may be measured directly with an inexpensive humidity probe or calculated, using a wet bulb/dry bulb thermometer and the appropriate tables.

Taking a hypothetical example, assume that atmospheric conditions are 20^oC and 80 per cent RH. The VPD is calculated by subtracting the value of the vapour pressure at 20^oC and 80 per cent RH outlined from Table 2 (19 millibars) from the vapour pressure at 2O^oC and 100 percent RH (23 millibars).

That is, VPD = vapour pressure at 100 per cent RH minus vapour pressure at atmospheric RH = 23 millibars - 19 millibars = 4 millibars

In the above example, the calculated VPD is small (4 millibars) and glycerining will be slow. It can be speeded up by heating the solution. Solution temperature should not be increased beyond about 40^oC, since there is a risk of killing the foliage.

Other factors

Water quality has been found to have no deleterious effect on the uptake of humectants (except possibly where calcium levels are extremely high). In fact, salts such as sodium chloride (NaCl) and potassium chloride (KCl) enhance uptake when added to the humectant solution at between 5 and 10 g/L. Similarly, a solution pH in the range 2 to 8 does not affect uptake.

Sweating

The amount of water that a humectant will hold is dependent upon the atmospheric humidity. At very high humidities (over 80 per cent), a small variation in humidity will greatly affect the water holding capacity of the humectant. 'Sweating' occurs when a sudden drop in humidity from a high level results in a drastic reduction in the water holding capacity of the humectant, which then releases free water. Because this water cannot evaporate quickly enough, it collects as droplets on the surface of the plant material where it provides an ideal environment for bacterial or fungal growth.

Sweating foliage should be hung in an area with plenty of air circulation to allow rapid evaporation of this surface water. Sweating can be minimised by:

• keeping the level of humectant in the plant tissue as low as practicable;
• storing glycerined foliage at low humidity, and
• avoiding exposure of glycerined foliage to conditions where a rapid decrease in humidity will occur (that is do not open storage or drying sheds on a fine day immediately after a week of rain).

Glycerined foliage destined for humid climates can be sealed in plastic before shipping, to prevent excessive moisture absorption in transit

Dyes

Dyes may be added to the humectant solution. Acid dyes (that is food dyes) generally produce good results when added to the uptake solution. Basic dyes can be used in the immersion method. Most humectants, especially glycerol, cause foliage to brown. The darker dyes, green, red, blue and black will easily mask this discoloration. It is often beneficial to sun bleach uptake-dyed foliage for about a week after glycerining to bring out the full intensity of the dye.

Pastel colours require the foliage to be bleached before dyeing and glycerining, to remove all background colour. It is imperative that all traces of bleach be removed from the foliage before attempting to dye. Either sulfuring, or dipping the foliage in sodium metabisulfite, before immersion glycerining and dyeing will ensure that residual bleach is removed. See also Farmnote no. 31/89 'Dyeing cut flowers and foliage' (Agdex 280/52) = AgFax Document No. 23414.

Hygiene

Glycerining solutions provide an excellent environment for the rapid growth of bacteria and fungi. These microorganisms may build up to such levels that they block stems and prevent solution uptake. Buckets used for glycerining should be kept clean. Residue should be scrubbed out and the buckets preferably sterilised with 1 per cent bleach (sodium hypochlorite) between uses. The high cost of glycerol means that the solution must be re-used several times. Thus, a biocide should be included in the solution to suppress pathogens.

Benzalkonium chloride (for example, Alginox®) at a concentration of 0.2 g/L is an effective biocide. Copper sulfate (0.2 g/L) may also be used unless it is planned to bleach the foliage at a later date. Copper catalyses the decomposition of bleach and should be excluded from bleaching solutions. Chlorine releasing compounds such as sodium dichloroisocyanurate (DICA) at 0.2 g/L are excellent biocides but must be replenished regularly because they break down within a few weeks. Organic fungicides such as Benlate® should not be added to the glycerining solution because they are not water soluble and may clog stems.

Acid dyes are incompatible with most of the above biocides. Hydroxy quinoline sulfate (HQS) is one of the few biocides that can be included with acid dyes. HQS is available as a fresh flower biocide (for example, Chinosol®) and should be used at 0.2 g/L of active ingredient.

Economics

Glycerining (with glycerol) costs approximately three cents per stem (in late 1989). The glycols are more expensive and may be difficult to obtain. Sorbitol is the cheapest of the readily available liquid humectants. Some quaternary ammonium salts show promise as humectants. However, data on their water holding capacity is not available.

Storage and transport

Cardboard cartons are used for storing glycerined foliage during transit Wax- coated or plastic-lined cartons can be used for shipment to humid climates to prevent contamination by atmospheric moisture.

Humectant quantity

The quantity of humectant needed for a supple product is dependent upon both the nature of the plant foliage (is it naturally brittle?) and the humidity of the intended market. Because it is the water that the humectant 'binds' which provides much of the plasticising effect on the foliage, relatively less humectant can be used for a market where the humidity is high. It is convenient to consider final market humidities as either dry (about 30 per cent RH), intermediate (about 60 per cent RH) or humid (about 90 per cent RH). Humidity ranges for major export markets are listed in Table 3.

Table 3. Relative humidities at sources and markets of glycerined foliage

* Mean monthly minimum or maximum

 

Location	Maximum % RH*	Minimum % RH*	Yearly average	Climate classification
Perth	73 (June)	53 (January)	62	Intermediate
Albany	77 (May)	73 (January)	75	Humid
Merredin	74 (July)	42 (January)	55	Dry
Sydney	77 (May)	63 (November)	69	Intermediate
Melbourne	75 (June)	57 (January)	65	Intermediate
Brisbane	72 (March)	66 (November)	68	Intermediate
Amsterdam	80 (August)	70 (January)	77	Humid
Auckland	80 (July)	74 (January)	78	Humid
Hong Kong	85 (April)	69 (November)	79	Humid
London	89 (December)	70 (June)	81	Humid
New York	76 (February)	63 (August)	74	Humid
San Francisco	78 (August)	70 (February)	72	Intermediate
Tokyo	80 (August)	70 (January)	80	Humid

Glycerol (glycerine) is the most widely used humectant. Glycerol application rates for some commonly preserved foliage lines have been determined experimentally. The data listed in Table 4 (below) refers to the number of grams of glycerol required to retain suppleness in one kilogram of fresh foliage. Note that the lower value of the range suggested is applicable to a humid market and the higher value would be required for suppleness in a dry environment. Some broad leaf eucalypts and native bamboo have been found to require high levels of glycerol to prevent leaf curl. Export of such products to humid markets requires special care because the product is especially liable to 'sweat'.

Table 4. Quantity of glycerol required for preserving some common foliage lines (g/kg fresh weight)

 

Species	Humid	Dry
Leucadendron	100	150
Eucalyptus	200	300-400
Bookleaf (Daviesia cordata)	200	300
Kangaroo paw (Anigozanthos)	200	400
Native bamboo (Leucopogon verticillatus)	300	400

Consider the data presented in Table 4 as a starting guide only. It may be necessary to vary the quantity of humectant in order to arrive at the optimum preserved product. It is prudent to err on the side of less glycerol (where leaf distortion is not a factor), because the danger of 'sweating' will be reduced.

Foliage preserved with a humectant will pick up moisture in a humid environment, and this moisture will increase its suppleness. Therefore, material preserved at the height of the Australian summer, where the humidity may be as low as 10 per cent, may appear dry and brittle. However, when exported to a more humid environment, the product will pick up atmospheric water and increase considerably in suppleness.

Humectant dilutions

Having determined the amount of glycerol for the desired end use, dilute it with sufficient water to give a concentration of about 20 per cent v/v or 1:4 (one part glycerol to four parts water). For plant species where leaf or flower drop can occur during glycerining (for example, Stirlingia), increasing the glycerol concentration to about 30 per cent (1:2) can minimise the problem. Leucadendron glycerines best when the glycerol is diluted to about 10 per cent v/v (1:9).

Note that most humectants are viscous liquids, and should be thoroughly mixed with the water by stirring; otherwise, they will settle to the bottom of the container.