Les Nesbitt is a founding member of the Native Orchid Society of South Australia and is our most experienced terrestrial orchid grower. The following four posts on growing are from his notes and pictures .
Australian terrestrial orchids have been grown in pots in Adelaide for more than 50 years. Nowadays with a wider range of species and hybrids available there are an estimated 300 cultivars successfully growing here. When the cultivation of the fungus dependent terrestrials is fully understood this number will increase dramatically.
Australian ground orchids are cool climate plants that follow an annual growth cycle comprising 6 – 8 months as growing plants under cool (5 – 20°C max, 0 – 14°C min) moist conditions and 4 – 6 months as dormant tubers in hot dry (18 – 40°C max, 12 – 30°C min) conditions. All species like good air movement and will not thrive in a stuffy humid atmosphere especially if temperatures are high.
In South Australia, terrestrials are grown in shadehouses with 50% cloth on the roof and sides. This lets the rain soak the pots and flush out salts from tapwater use. Some growers add a second layer of 50% shadecloth in summer to lower pot temperatures.
It is very important that winter sun and breezes reach your plants so place the shadehouse away from the winter shadows of buildings and evergreen trees. A shadecloth cover or evergreen tree to the southwest and overhead will give protection from frost, hail and storms. Light frosts of -2°C do not worry the majority of species. Galvanised mesh benching about 750mm high will deter slugs and snails and is a convenient height for observing the pots. Watering with rainwater is better than Adelaide tap water. Fungi and orchids do not like salt.
Some species prefer heavy shade, others full sunlight, but most will adapt to a wide range of light intensity. If the leaves and stems are weak and limp or if the rosettes are drawn up to the light, then the shading is too dense and the amount of light should be increased. The spring flowering species like higher light intensities at flowering time and flowers may have pale colours under dull conditions.
The soil should be kept moist at all times during active growth by watering gently if there is no rain. Hand watering is especially necessary in spring as soil in pots dries out more rapidly than in the garden. Watering must be done slowly so that the mat of needles on the surface of the pot is not disturbed. If pots are allowed to dry out during the growing season, the plants may go dormant prematurely.
Slugs and snails love these plants and must be kept under control. Raising the pots off the ground on galvanised steel benching is very effective in controlling these pests. Thrips, aphids, red spider and caterpillars may cause damage. Blackbirds can scratch out small orchids. Various rots can destroy plants. Orchids showing virus like symptoms should be burnt or dumped.
Be very careful with fertilisers because some terrestrials are easily burnt or even killed by overuse. Diuris and Pterostylis are very hardy and will benefit from weak applications of foliar feed in the early growth stages.
The new tubers are produced in winter – spring. The fast multiplying types form several tubers per plant each year. Sometime in October – November, the leaves go yellow and then brown and dry, as the days get longer, hotter and drier in late spring. After the leaves have turned yellow, let the pot dry out completely to dry up the old roots and tubers otherwise they may turn into a soggy mouldy mess and rot may destroy the adjacent new tubers.
The pots can be knocked out and the tubers examined in summer without harm, in fact we find at the Nursery that the best results are obtained if the tubers are repotted in half fresh soil mix each year. Our soil mix is 40% loam, 50% sand and 10% organic matter with a little blood and bone fertiliser added. A 5 mm sieve is a useful tool for separating tubers from soil. Replant the dormant tubers with the tops 20 mm deep. Cover the soil surface with a mulch of sheoak needles, chopped to 20 – 50 mm lengths, to prevent soil erosion & aerate under the leaves. Repotting is normally done in November, December, January and February in South Australia. Ideal pot sizes are 125 – 150 mm standard plastic pots.
Keep the pots shaded and allow the pots to dry out between light watering until mid February when they should be set out in their growing positions and watered a little more often. The tubers of some species will rot if kept wet during the dormant period, others will produce plants prematurely which are then attacked by pests such as thrip and red spider and fungal diseases in the warm weather. Each tuber sends up a shoot to the surface in autumn and leaves grow rapidly in late autumn – early winter as temperatures fall and the rains set in. Pterostylis are usually the first to appear in March followed by Diuris and Thelymitra in April, Caladenia in May and Corybas in June – July.
Sun loving species like Diuris, Microtis and Thelymitra prefer a brighter location for good growth. Corybas like the shadiest corner in winter.
|Thelymitra ‘Kay Nesbitt’ cultivar (Fast Multiplier)|