Drying cut flowers and foliage

Page last updated: Tuesday, 13 January 2015 - 1:38pm

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Preparation

Excess foliage is first stripped from the stem and the stems are bunched for ease of handling. Rubber bands are the most practical bunch ties because they take up any shrinkage that occurs on drying.

The bunches are often hung on mobile racks. Large flowers (some proteas) may best be dried individually supported on wire mesh. Red and green kangaroo paws dry best if laid flat. Some species require a glycerol pre-treatment to prevent excessive brittleness developing (see Table 1).

Fumigation with sulphur dioxide is routinely carried out before drying, both to kill pests (insects and fungi) and to minimise colour loss. It is important to allow good air circulation around the bunches during drying to avoid the build-up of stale, humid air which may encourage fungal growth.

Pre-treatment with glycerol

Glycerol (glycerine) is a hygroscopic compound, that is it attracts and holds water. This water-holding ability ensures that plant foliage treated with glycerol remains supple and will not dry to the point of brittleness.

Table 1 Species requiring glycerol treatment prior to drying
Botanical name Common name
Adenanthos cygnorum woolly bush
Anigozanthos kangaroo paw
Athertonia diversifolia blue almond tree
Brassaia actinophylla umbrella tree
Conospermum sp. smokebush
Eucalyptus sp. eucalypt
Grevillea sp. grevillea
Leucadendron spp. leucadendron

Ozothamnus diosmifolius

sago bush (wild rice)

Pittosporum

pittosporum

Podocarpus

emu bush
Pteridium esculentum bracken fern
Sticherus umbrella fern
Stirlingia blueboy

Foliage can be soaked in a solution (usually 50%) of glycerol in water. About three weeks is required for full absorption using this method. After removal from the glycerol solution, the foliage can be lightly rinsed in water.

A more practical alternative, suitable for many species, is to stand the stems upright in a vessel containing the glycerol solution in a warm dry place. Usually a solution of 10 to 30% glycerol in water is satisfactory. Actively growing foliage gives the best results. Species which normally undergo cyclic growth patterns (for example, leucodendrons) may only take up the glycerol solution if picked during a growth 'flush' (usually mid-summer). At other times the slower absorption by soaking must be used.

The leaves will become supple within six to 10 days and at this point the foliage should be removed from the solution before too much glycerol is absorbed. If this happens, the foliage is unsuitable for humid climates (for example, Japan) as it will attract excess atmospheric moisture. This phenomenon is known as 'sweating' and is characterised by beads of unsightly, oily-looking water on stem and leaf surfaces. Such material is also highly susceptible to fungal infection.

An unfortunate side effect of glycerol is that it makes colours run and can result in overall darkening or browning. Browning is usually less severe with young foliage. Absorption dyes can be added to the glycerol solution to mask slight discolourations or to highlight leaf veins.

Author

Aileen Reid