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Culture of Terrestrial Australian Orchids

Deciduous terrestrials thrive in a shadehouse of 50-70% shadecloth. In very cold areas, orwhere summer rain is heavy, a plastic roof is usually added. Light frost to -2oC does not worrythe majority of species. All terrestrials like good air movement and will not thrive in a stuffy

humid atmosphere, especially if temperatures are high. Some species prefer heavy shade,others full sunlight, but most will adapt to a wide range of light intensity. The spring floweringspecies prefer highter light values at flowering time. It is essential to keep pots up off the groundon benches to deter slugs and snails. I like to use plastic pots because they are easier to cleanand sterilize. Pot size should be neither too big nor too small. I recommend 125mm standardpots up to 175mm squat pots for specimen groupings of 20 plants.

The potting soil must be kept uniformly moist during active growth. If the pots are allowed to dryout during the growing season, the plants may become dormant. Fertilisers are not necessary,although Pterostylisspecies are very hardy and will benefit from weak applications of foliar feedapplied whilst the leaves are developing. New tubers are produced in winter-spring. The colonytypes form several tubers per plant and within a few years the pots would become overcrowded

if not repotted. I recommend annual repotting for these. Some of the showier species produceonly one new tuber each year and have to be propagated from seed. Some of these can bemade to produce a second tuber by carefully twisting off the new season's tuber inSeptember/October and replanting the plant with the old tuber still attached for another month ortwo. This method works well with Diurisand the rufagroup greenhoods.

As the days get hotter and drier in late spring, the leaves of terrestrials go yellow and thenbrown and dry. After the leaves have turned brown, the pots are allowed to dry out completely todry up the old roots and tubers. Terrestrials must be given their own growing area, well awayfrom evergreen plants which are watered regularly in summer. The tubers may rot if kept wet inhot weather. Seed pods ripen before the plants become dormant. Pods are checked daily andpicked as they start to split open. Seed is stored in paper envelopes until autumn.

In summer the plants are knocked out of the pots and the new plump, firm tubers are repottedinto fresh soil mix. My mix is 45% loam, 50% sand and 5% peat moss with a small amount ofblood and bone fertiliser added. It has a pH of 5.5. Growers in other states use coarser mixescontaining fine gravel and with leaf-litter or buzzer chips in place of peat moss. The new tubersare replanted with the tops 20-40mm below the soil surface. A thin surface mulch of Casuarinaor Pinus radiataneedles, chopped to lengths of 20-50mm, prevents erosion and keeps theleaves clean and healthy, as well as improving the appearance of the pot. Repotting is normallydone in November, December or January.

Each tuber sends up a shoot to the surface in autumn. The leaves grow rapidly in late autumnand early winter as the rains set in. Seed can be sprinkled on top of the pots around mature

plants in autumn. Protocorms develop in the cool, wet winter conditions and seedling leavesappear in spring. Seedlings produce tiny tubers by summer. Only the largest usually survive thelong dry dormancy period of 4-6 months.

Some species set seed unaided but most require hand pollination. I use a piece of pine needleto transfer pollen from one flower to another of the same species. The flower collapses within afew days if pollination is successful. Seed pods develop rapidly and in springtime can ripen in 4-6 weeks.

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The four commercially important deciduous terrestrial genera in cultivation are Caladenia,Diuris, Pterostylisand Thelymitra. Each genus has a large number of species, although notmany Caladeniaare in general cultivation. I am growing more than 50 terrestrial hybrids in potsand have a number of others in flask.

We have been very successful with the sun orchids or Thelymitra. All the colour of the rainbow,

including the most beautiful blues, are found in the sun orchids. For exhibition work Thelymitraare poor subjects because the flowers close at night and will not open unless the temperaturerises above 22oC. They can be made to open on cool sunny days if the pot is placed inside aclosed car. Thelymitraare all spring/summer flowering orchids in southern Australia. They arevery striking plants, some growing more than 50cm tall with up to 20 flowers. The smallerspecies are the easiest to cultivate.

There are a few evergreen terrestrials from the tropics which are widely grown. Two which come

to mind are Phaius tankarvilliae the Queensland swamp orchid, which has 90mm pink, white

and brown flowers and Calanthe triplicata the Christmas orchid, which has a cluster of white

flowers on top of a tall stem.

Caladenia flavais a very distinctive species because of its bright yellow flowers which oftenhave crimson spots. It has a broad, hairy basal leaf up to 25 cm long. The 30-40 mm diameterflowers are often solitary but up to four flowers may be borne on a slender stem about 30 cmhigh. Flowering occurs in spring and the plants become dormant in summer when they die backto an underground tuber.

Like most terrestrial orchids, C.flavahas fairly specialised cultural needs and is cultivated mainlyby orchid enthusiasts. Generally the plants are grown in pots in a freely draining, sandy mix.They require good air circulation in a protected position of about 50% sun during the growingperiod from autumn to spring. During this growing period the plants must not be allowed to dryout. After the leaves have turned brown in late spring to early summer the pots are allowed to

dry out completely. Repotting of tubers can be carried out in summer.

Australian Terrestrial Orchid Mix

The mix I use 1.5 parts sand; 2 parts pine based potting mix, 1 part eucalypt leaf mold with a bitof blood and bone meal thrown in. It's adapted from a mix recommended by a number ofVictorian terrestrial growers: seewww.anosvic.org.au/ANOS_Terrestrial_Cultivation_Notes.pdf?The original idea behind the ANOS mix was to provide a steady source of decaying organicmatter (bone meal>leaf mold>wood) to keep the fungi happy.If you have Eucalypts growing locally, I'd use them as a 'tried and tested'leaf mold. Eucalypt leaves are usually recommended as they are quite fibrous so they don't lose

their structure and turn into a soggy mess like many of the softer leafed trees. I do compost myown eucalypt leaves for my mix as it's not actually that easy to find natural leaf mold under theeucalypts in suburban Melbourne. The local parks and curb plantings are all mowed andmulched and any built up leaf litter is usually swept up by the local councils before it has achance to rot down naturally. I haven't tried composting the entire media before I use it, though.

Repotting can disrupt the fungi in the pot so the frequency of repotting is a balance between notdisturbing the plants unnecessarily, not allowing fast multipliers to overcrowd themselves and

http://www.anosvic.org.au/ANOS_Terrestrial_Cultivation_Notes.pdfhttp://www.anosvic.org.au/ANOS_Terrestrial_Cultivation_Notes.pdfhttp://www.anosvic.org.au/ANOS_Terrestrial_Cultivation_Notes.pdf

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remembering to repot slow multipliers before the potting mix compacts too much. Whenpossible, most people plant multiple tubers in the pot as they're much showier that way.Generally fast multipliers like most Pterostylis are repotted yearly, slower multipliers likeThelymitra, Diuris and the easier, fast multiplying Caladenia like latifolia can be left for 2-3years. Solitary and very slow multipliers like most Caladenia tend to be repotted about every 3to 5 years. 5 years is probably pushing the limits of most terrestrial media but it goes to show

how much people are reluctant to disrupt Caladenia fungi in the pot when a plant is growingwell.

As for deflasking the seedlings, I wash the flasking media off the seedlings so that the sugar etcdoesn't encourage the fungi. This sounds counterintuitive but deflasked terrestrials are just assusceptible to pathogenic fungi as any other orchid. Even with symbiotic flasking, the germinatorfungi can start to kill the seedlings if the media encourages too much fungal growth. It'sprobably best to ask for washed seedlings. There is probably more risk of damaging the joinbetween the tubers and the leaves if flasked plants are shaken up too much in transit. I usuallyplant them into a fresh mix of 1 part potting mix: 1 part perlite.Many of the local growers go the extra step of pasteurising the mix to reduce, but not totallyeliminate, the fungi in the mix. This way you ease the orchids into associating with the right fungi

rather than swamp them with lots of fungi and hope they can find their friends in the crowd.Planting out into compots is fine. I don't think there are any advantages to planting these orchidsinto individual pots. On the slight chance that there are any really special seedlings that youwant to separate out from the group, it can be done easily when the plants are older and moreestablished.

The mixes we use are slightly acidic to neutral, ie around pH 6-7. If you find the pH of your finalmix is too acidic, it's OK to add lime to bring the pH back up. That being said, I did at one stagehave a group planting of Pterostylis and native Drosera in my terrestrial mix using peatmossinstead of potting mix and the orchids grew fine so acidity may not be that much of a problem.