Australian Native Terrestrial Orchids – A Beginner’s Guide
It is estimated that there are 25,000 to 35,000 orchid species in the world today, of that Australia has over 700 species of orchids, where approximately 25% are epiphytic or lithopytic and 75% are terrestrial.
The majority of terrestrial species are perennial herbs that have a life cycle which involves the plants dying down (dormant period) usually over the summer months. A few are evergreen; some are climbers, while still others come above ground only to flower.
There are three distinct groups of terrestrial Orchids in Australia, it is best to divide them into culture similarity.
Group 1. The northern type, such as Phaius, Calanthe, Malaxis species. Most are evergreen with pseudobulbs, fleshy leaves and typical orchid roots, not covered in this presentation.
Group 2. The semi or Holo saprophytic, very difficult if not impossible to grow in pots. This group contains some of the most unusual orchids in the world. In general, saprophytic plants lack the green chlorophyll cells that manufacture the plants sugars and starches. To overcome this, the group depends wholly on a symbiotic relationship with a soil fungus.
Some saprophytic orchids grow in or close to a carbon source, such as decaying wood, and rely on the mycorrhizal fungus for transfer of nutrients. Others are known as hemiparasites, have a 3-way relationship involving a fungus and a suitable species of host plant, not covered in this presentation.
Group 3. The main genera and the easiest to grow are: (A) Pterostylis, Acianthus and Corybas species that usually grow in moist, humid leaf litter and (B) Diuris, Calandenia, Calochilus, Thelymitra and Prasophyllum species which grow in drier, sandy type soils with higher light. They are terrestrial orchids that grow from an underground organ which is actually a swollen root. These organs may resemble elongated rhizomes but mostly they are rounded or ovoid and resemble tubers.
Food for terrestrial orchids is obtained from the soil or leaf litter in a complex exchange with a mycorrhizal fungus. The mycorrhizal fungus act as food gatherers and inhabit areas in the roots or underground stems of the orchid and the food products are transferred from the fungi to the orchid
Annual growth cycle
At the beginning of the growing period (which for most species is autumn) a stem emerges from the tuberoid and grows to the soil surface. It produces leaves and/or flowers.
Most terrestrial orchids have formed a new tuberoid to replace the old one by flowering time.
After flowering the food reserves of the orchid are withdrawn back to the tuberoids.
All above-ground parts wither and dry out and the plants survive the hot, dry summer months as dormant tuberoids buried in the soil.
POTTING MIX.
1 Part leaf mould
1 Part wood shavings
1 Part loam
2 Part coarse sand
1 dessert spoonful of blood and bone per 9 litre bucket.
Drainage of this mix varies with the particle size of the ingredients, generally, the larger the particles, the faster the mix will drain, extra coarse sand and/or wood shavings increases drainage, extra rich loam and/or decomposed leaf mould reduces drainage.
The quantities of the ingredients can be varied according to the individual requirements of the species being grown.
I have also tried Debco native potting mix 3 parts plus 1 part of propagating sand.
CONTAINERS.
Plastic pots are recommended, the minimum size should be 100mm. Pots smaller than this dry out too quickly. The recommended size is 150mm, as a guide, a 150mm pot will satisfactorily hold 20 tubers of average size, Larger pots can be used for larger numbers of tubers, but special care needs to be taken as the larger volume of mix tends to retain more moisture. POTTING
PROCEDURES.
Colony forming terrestrials should be re-potted each year as overcrowding is more likely to lead to disease. Colony forming plants can multiply with up to 5+ new tubers for every old tuber. If not re-potted the chances are that some tubers will grow out of the drain holes of the pot.It is not so important to re-pot non-colony forming terrestrials every year, Non-colony forming plants replacing one for one tuber. To re-pot terrestrials, I’m start with emptying the pot into a tray and by hand finding all the new tubers, some species are more difficult than others as some of the new tubers can be very small.
1. Fill about two-thirds of the pot with mix.
2. Arrange tuberoids in the pot with growing eyes up. The tops of the tuberoids should be about 30mm below the final level of the mix.
3. Top up the pot with mix, and add label to pot, with plant name, number of tubers and date.
I mulch with a thin layer of Casuarina needles on the top of the potting mix surface to reduce disturbance when watering and to slow down the drying out of the upper section of the potting mix and, hence, reduce the frequency of watering.
Watering
How and the frequency of watering depends on: -
1) The species of orchid.
2) The potting mix components and their size.
3) The time of the year.
4) The day and night temperature.
5) Air movement around the pot, especially wind.
6) The amount of sunlight reaching the pot.
7) The humidity of the environment in which the pot and plant are kept will affect moisture loss.
Thus, getting the watering correct involves observation, practice and a few aids to help.
A useful aid is to make up some extra pots without orchids, then you will be able to dig into the pot and see if watering is required. You can also pull the name tag from a pot and observe the dampness on the end that has been sitting in the mix.
The pots need to have moisture not water in the potting mix where the tubers resides, not too little so the plant dehydrates, or too much so the plant cannot get enough oxygen through its roots.
Light and Humidity
The amount of light varies depending on the genus, Pterostylis and Acianthus prefer shadier conditions than the Diuris, Caladenia and the aptly named Sun Orchids Thelymitras (So called because the flowers open as the sun rises and close by night).
All these species resent stagnant humid conditions preferring an open position with plenty of air movement, as plants can get attacked by fungal infections.
Fertilizing
A small percentage of organic style fertilizer like blood and bone can be added to the potting mix. This year I’m trying 1 or 2 pots with extra fertilizer to see what difference it makes
Pests
As for pests, the usual suspects Slugs and Snails can do immense damage in a very short time. Baits for these can be a necessary evil. Keeping plants suspended on mesh benches is a good deterrent. Thrips and Red Spider can at times also cause problems.
Temperature
As a general rule, plants grow most rapidly between the temperatures of 15 and 30° C. although most Australian terrestrials can tolerate freezing, it should be avoided if possible.
Few terrestrial orchids grow in alpine areas. And those which do flower mainly in spring and summer. (For example, Corybas dienemus, endemic to Macquarie Island have a flowering period between November and January.)
Housing.
Without doubt, the best form of housing for terrestrial orchids is a specially constructed shadehouse.
The shadehouse should have a translucent solid roof to protect plants from excessive rain and light, and two or three walls of shade cloth to protect plants from strong winds, but still give good ventilation.
However, you can grow terrestrial orchids in a variety of places around the home.
Under trees (provided pots are protected from drips), on a porch or veranda, in a sunroom or anywhere indoors where indoor plants grow well. If a saucer is used under a pot, insure that it does not retain water.
The mix in pots which are not under a solid roof must be very well draining to prevent tuberoids from rotting from remaining too wet for too long.
I have also planted some spare tubers in the garden with good success.
Plants can be sourced from:
some ANOS Group’s that have tuber banks;
specialist orchid nurseries; and
sales tables at orchid shows.
