CULTURE NOTES FOR EPIPHYTIC ORCHIDS in ADELAIDE 2016

Dendrobium speciosum

Epiphytic orchids grow on trees or rocks (lithophytic), where they are dependent on their host for support but not for food.

CULTIVATION

The majority of Australian epiphytic orchids can be easily grown in cultivation.  Most can be grown in Adelaide if the correct cultural requirements are provided.  These include controlled glasshouse conditions, shadehouse conditions and, in some instances, in the garden.  Only a few species are able to tolerate the cold winter months in Adelaide without extra protection, and all need protection from frost.

CONTAINERS AND MOUNTS

Plants can be grown in pots or mounted on an appropriate substrate. Pots may be either plastic or terracotta.  Terracotta pots are porous and dry out more quickly than plastic.  If terracotta pots are used, their drainage holes may need to be enlarged to give very good drainage.  Plants should be potted into the smallest pot, which comfortably accommodates the base of the plant.

Plants may be mounted on materials such as compressed or natural cork slabs, branches of rough barked trees, black weathered tree fern slabs and pieces of weathered hardwood.  Brown tree fern slabs contain substances, which are toxic to orchid roots and are not suitable.  Those species that have a pendulous habit e.g. Dendrobium teretifolium should only be mounted.

POTTING MIX

Most potted orchids require a mixture made up of bark chips (fir or pine), to which may be added charcoal, gravel or polystyrene chips, in which to grow.  Bark used should be aged and preferably purchased as graded hammer-milled bark, not shredded bark.  Fresh pine bark contains compounds, which are toxic to orchids.  Before use fresh pine bark should be soaked in water changed regularly, to remove toxins.  This may take 3 weeks.  If in doubt as to the freshness of the bark, treat as above to be sure.

Depending on the size of your plant, bark may vary from 5-7mm up to 20mm in diameter, and sieved if necessary to remove fine particles and dust.  Other substances such as scoria, leaf mould and coarse grit may also be added according to the requirements of the particular species involved.  Whatever the substrate, be it a slab or potting mix, the essential thing with all epiphytic orchids is to always provide good drainage for the plant’s root system.  This ensures no, or minimal, root rot of plants.

Repotting is necessary when the potting mix breaks down resulting in poor drainage, the medium goes stale or when the plant over grows its container.  The best time to repot is during the spring, after flowering, when the plant starts to actively grow again.  Try to repot every 2-3 years.

Potting on:  If the plant has overgrown its container and the mix has not deteriorated, it can be potted on into the next sized pot with minimal disturbance to the root system.

D kingianum composite (2)

GROWING ENVIRONS, HOUSING

Garden Culture

Several species may be grown outside in Adelaide, provided they are given a position sheltered from frosts and hot drying winds.  They should receive daily supplementary watering during the summer.  They may be tied on to trees with rough non-deciduous bark or grown on rocks.  Microclimates can be created in areas of the garden using screens for protection and other plants to help maintain a humid atmosphere.

Bush house, Shadehouse

These structures are built to give protection from frosts, strong winds and sun and to provide extra humidity for plants.  They may be covered with shadecloth or tea-tree and should have a solid south wall.  They provide protection, but still allow for good air circulation around the plants.  A water impervious roof, e.g. fibreglass or polycarbonate sheets, will protect plants and flowers from excess water in the winter.


Unheated glasshouse

An unheated glasshouse gives more protection to the plants, achieving higher temperatures during winter days, and better humidity.  It may be made from glass or other materials such as fibreglass or polycarbonate sheets.  Additional shading with shadecloth or paint is necessary from October to March-April.  Adequate ventilation must be provided, by using ventilators under the benches to let in fresh air, and roof ventilators to let out hot air.  Alternatively, air circulation can be achieved using fans.  All orchids love fresh air.

WATERING

All plants need to be watered frequently from October to April, during the growing period.  Most species require watering once a day or twice a day if the weather is particularly hot or drying.  Ensure that plants dry out between waterings.  During winter, watering once a week should be sufficient for plants in a glass house environment, although plants which are mounted may be misted (a very fine spray) more frequently.  Water early in the morning of winter days to ensure that the leaves of the plants have dried off by night.  Water lodging in leaf axils in cold, comparatively still conditions, renders that area liable to fungal attack.  Humidity may be maintained by watering the floor and under the benches, particularly in summer.

Rainwater, if available, is preferable to mains water, which can. In some cases, increase in salinity to a level, which is harmful to good plant growth.

FERTILISING

To promote healthy growth of all epiphytic orchids, a supplement of half strength liquid fertiliser every two weeks may be used during the growing season of the plant, i.e. November to April.  Mature potted plants can be sparingly fertilised with slow release pellets.  Too much fertiliser will lead to a salt build up (especially in charcoal), which will harm the plants.

PESTS

Pests will become a problem in any shadehouse or glasshouse if the grower does not keep a watchful eye out for them.  The shadehouse or glasshouse should be kept free from weeds, decaying organic matter and rubbish, as these are the places where pests feed and accumulate.  Overcrowding of plants will also encourage pests to thrive.

Pests can be easily removed by squashing if they are in small enough numbers.  A pest strip hung in the glasshouse successfully controls many pests. Unfortunately the environment of a glasshouse, which suits orchid culture, also provides a suitable environment for the spread of pests.  Poisonous chemical sprays should only be used after non-toxic preparations have been unsuccessfully used.  These chemicals also destroy the natural predators of insect pests, upsetting the natural balance.

Caution should be used when handling chemical sprays as many are very toxic to the user as well as the pests.  The manufacturer’s directions and warning labels should be read carefully and recommended strength adhered to strictly.

DISEASES

Australian epiphytic orchids are generally disease free.  Fungal infections may occur, susceptible areas being new growths, especially in young plants.  These can be kept to a minimum by maintaining good air movement and avoiding water remaining in leaf axils for too long.  Broad spectrum fungicides are suitable to control severe infections.

PLANT CARE

Removal of any dead leaves, pseudobulbs, etc, not only enhances the aesthetics of the plants, but also lessens the chance of further deterioration.  These areas are also the places where pests may accumulate or diseases harbour.

Dendrobium bigibbum

Dendrobium bigibbum

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