Monthly Terrestrial Orchid Culture—March

As stated last month, this is the second in the series of terrestrial culture notes for growing orchids in Adelaide.

Terrestrial Culture—March

Les Nesbitt

The growing season is underway although much of the activity is underground out of sight early in the month. Repotting should be completed by now. Repotting tubers with long shoots is a tricky business requiring very gentle handling. Broken shoots and the death of some plants can result. It is better to leave them until next summer.

The weather can be hot up until equinox on about March 21st.  Be aware that autumn is a time of rapid change. Day-length decreases by 2 hours in the 6 weeks from the 1st of March. Our orchids respond to the longer cooler nights faster than we do. All pots should be in their growing positions for the coming winter. Increase watering in March so that by equinox the mix is damp right through to the bottom of the pot. The first Eriochilus cucullatus flowers are usually open by the last day of March with the majority blooming in April. The buds resemble a grain of wheat when they first emerge.

Eriochilus collinus
Eriochilus collinus (syn Eriochilus sp Adelaide Hills, Eriochilus aff cucullatus)

Thrip can be a major problem this month. Thrips love to suck on the flowers and will cause the flowers to shrivel up in a day or two. If using a pressure pack fly spray to kill thrips, hold the can at least half a metre away or you can freeze the flowers with the propellant. Repeat the spray every few days.

Pull out any weeds that germinate while they are still small. The early Greenhoods will be showing leaves and some of the blue tag Diplodiums may be showing buds. The Greenhoods will like a weak soluble fertiliser sprayed on their new leaves as they develop.

Deflasking can be done after equinox. April is the best month to deflask terrestrials as it is cooler and more humid with enough sun to harden the leaves before the cold and damp of winter. Flasks are often the only way to get the slow multiplying terrestrial orchids. Seedlings in flask that have tiny tubers establish more successfully.

Diuris tricolour in flask

Remove the second layer of shadecloth at the end of the month or first week in April. Keep up the night time hunts for pests which get more active as the nights cool.

Autumn is a good time to build or extend a terrestrial growing area. A terrestrial house should be sealed to keep out birds and animals and have shadecloth or wire mesh sides to allow the breeze to move through. I prefer a roof of angled 50% shadecloth. Other growers use a solid roof of plastic sheeting. A solid roof means you have to water your pots by hand, which is more work. It is very important that winter sun reaches your plants so site the shadehouse away from the winter shadows of buildings, high fences and evergreen trees. Galvanised mesh benching about 750 mm high will deter slugs and snails and is a convenient height for observing the pots.

food healthy nature forest
Photo by PhotoMIX Ltd. on

Monthly Terrestrial Orchid Culture – February

The following article by Les Nesbitt is from Journal of the Native Orchid Society of South Australia, February 2019 Volume 33 No 1. It is the first of a monthly series that Les is planning to produce for this year.

It should be noted that February in Australia is late summer and dry; and that this article has been written for Adelaide growing conditions. Many of the terrestrial orchids have been dormant.

Terrestrial Culture — February

The excitement is building with the new growing season about to commence. First leaves on the early species may show this month so start looking. Look with your eyes not your finger. Many a new shoot has been broken by that dastardly finger. Keep the blue tag pots moist. Blue tag orchids include Diplodiums, Ptst. baptistii and Corybas hispidus, all species from the East Coast of Australia.

Repotting and Watering

Finish repotting as soon as possible. Many tubers start shooting this month and are easily damaged by handling. Move all pots to their growing positions for the coming winter. For local orchids adapted to a dry January-March, commence watering in the last week of February and increase watering in March. The water will run down the side of a dry pot and out the drainage holes leaving a dry plug of mix in the middle where the tubers are. Watering three days in a row should wet the pot right through. Continue light watering weekly, so pots do not dry out completely again. Top up the cut she-oak needle layer on pots as needed. This is very important for the fungus dependent species which do not get repotted often.

Diuris tricolour in pot
Topped with she-oak cuttings

Hunting the Grubs and Slugs

Start the nightly visits to pick off the slugs, snails, earwigs and grubs. Hunts are more successful on cooler nights after rain or watering. If the new shoots get eaten off as soon as they appear you might not even see them and wonder why your orchids did not come up.


If the names on labels are starting to fade rewrite them before the name is lost. Remember to pot up any spare tubers for raffles, stalls and the tuber bank later in the year.


The cauline group of greenhoods (Diplodium) from the eastern states are the first to shoot and ideally should have blue tags and have been repotted in January with watering commencing at the end of January. There are some 38 species in this group. Some come from high altitudes in NSW/Vic and start flowering there in February. They flower in March/April/May in Adelaide.

Diplodium in cultivation
Diplodium robustum – one of the cauline greenhoods, with both flowering and non-flowering plants

Points to note about Diplodiums:

  • Flowering plants look different to non-flowering plants. Flowering plants have small pointed leaves on the flower stem. Nonflowering plants have a rosette of rounded leaves flat on the ground. Usually there are only a small percentage of flowering plants.
  • They flower early in the growing season. Most flower in autumn with a few stragglers in winter. None flower in spring.
  • The rosette plants multiply and are easy to grow in regular terrestrial mixes. New tubers form in Autumn.
  • Diplodiums are not easy to flower in Adelaide. Flowers abort if too hot and/or too dry. Grow them in the coolest shady area there is. Keep pots shaded until late March. Local species are easier to flower as they flower in winter.
  • Poor tuber development from flowering plants is common. These plants sometimes die after flowering.
  • Flowering plants can be tall & slender and may need supporting with a wire cylinder. Stakes can damage the developing new tubers.


For additional information on growing terrestrial orchids click here 

A Timely Reminder

This article is reprinted from  Volume 39 No 11 December 2015 Native Orchid Society of South Australia Inc. Journal

Tuber Repotting Time is here

Les Nesbitt

Now that Australian terrestrial orchids have gone into dormancy it is time to think about repotting and preparing for the next growing season.

The best months for this activity are December and January.

I will limit this discussion to the easily grown colony forming terrestrial orchids as these are more likely to be available – for easily grown terrestrials, click here.


We need more terrestrial growers in NOSSA to feed the tuber bank and to supply spare pots for sale to the public at the Spring Show. I found it embarrassing to see so few terrestrials for sale at the 2015 Spring Show compared to the numbers available in years gone by.

Growing terrestrials is a rewarding hobby that does not take up much time or space and will pay for itself. Plus you are doing something effective orchids and the environment even if only the most common terrestrials are grown (eg the greenhoods and onion orchids). Consider easily grown, fast multiplying, Pterostylis curta (listed as rare in the SA Act) has been widely grown in NOSSA collections since the days Roy Hargreave’s wash trough when NOSSA was formed.

Once the basic principles are understood it to move onto the rarer species as artificially propagated plants become available in future as they surely will. Members can draw on the tuber bank in December to get started seriously about it as a group of volunteers will be needed within a year or two to help look after the output of a number of projects already underway or about to start.

Year 8 girls at Kildare College have been repotting the school’s terrestrial collection and this is how they did it.


Prepare all the materials needed including:

  • Pots
  • crocking material,
  • sand
  • organic matter
    • blood & bone, native compost, chopped up sheoak needles
  • 4B pencil and labels.


  • Water the pots lightly a day or two before repotting. The mix should be damp enough to not be dusty, yet dry enough to not stick to everything.
  • Remove the label, wash it in a container of water and stand it aside to dry.
  • Check on the label back to see how many tubers were planted last year.


Scrape off and dump the top layer of soil as this can be contaminated with moss, slimy bacteria and liverworts.

  • Tap out the plug of soil into a sieve sitting on a bowl. Pick out any tubers that are visible on the outside of the plug.
  • Gently break the soil apart and search for tubers while squashing the lumps of mix through the sieve.
    • Very small tubers may go through especially with Corybas. If you have not got a sieve do this operation on a sheet of newspaper.

Place the tubers in a dish so they do not roll away.

  • Count the new tubers to see whether they increased by 2, 3 or 4 times.
  • Discard anything left in the sieve (old tubers, roots etc.).
  • Work out how many new pots are needed to plant all the new tubers.

Add to the old mix in the bowl

  • a pinch of blood & bone,
  • a handful of sand and a handful of native potting mix.
    • Also add enough of these ingredients for each additional pot and mix the contents of the bowl together.

Select new or sterilised 125 mm standard pots

  • and place a square of shadecloth in the bottom to keep the sand in and critters out.
  • Pour in mix to within 30 mm of the top and ram down with your fist.
  • Place up to 10 tubers on top of the mix.
    • Lay tubers horizontally if unsure which is the top.

Labelling and finishing the task

  • Write out the orchid name on extra labels and fill in the numbers of tubers on the back for each pot.
  • Almost fill the pot with mix and tamp down.
  • Insert the label. Place a layer of cut sheoak needles on top of the mix.
  • Water the pots and the job is done.

For show pots use 175 mm or larger pots and plant 20 to 50 of the largest tubers available.

If the tubers have decreased or look unhealthy, throw out all the old mix and replant in new mix.

Repotting a Diuris

Related Articles:

Growing Terrestrial Orchids Part One of Four

Growing Terrestrial Orchids Part Two of Four

Growing Terrestrial Orchids Part Three of Four


When do I stop watering my Greenhoods?

This was the question posed to Les Nesbitt at the September monthly meeting.  Later there was some further discussion, of which see below:

When do I stop watering my Greenhoods?

The short answer is when the leaves go yellow and start to die off, usually in October- November. Allow the pot to dry out completely to dry up the roots and old tubers so that they do not go mouldy and rot the new tubers.

Australian terrestrial orchids form tubers underground. The mature plant dies back at the end of the growing season and enters a period of dormancy which for South Australian terrestrials is over summer.

A general principle of watering is to match the watering to the rainfall pattern. Whilst there is minimal rain over summer, when dormant tubers are in pots it is important to not let them stay dry for months and become desiccated. A light sprinkling every week or two is sufficient.

Pterostylis ‘Nodding Grace’ This is an hybrid between P. nutans and P. curta. Obviously it is not time to stop watering.

When do I start watering again? 

For the cauline group (Diplodiums) from South-eastern Australia start watering at the end of January as the tubers are starting to shoot by then. For other greenhoods start light watering in late February and gradually increase the water until shoots appear usually in March-April. Do not let the pots dry out once leaves are visible.

Diplodium robustum - one of the cauline greenhoods
Diplodium robustum – one of the cauline greenhoods. Note difference the between the leaves of the non-flowering rosettes and the flowering plants.

Other cultivated Australian terrestrial orchids require a similar watering regime although leaves of some appear later in May or June.

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