NZ orchid growers and enthusiasts have a very good reputation both nationally and internationally for growing exotic orchids of all types to perfection. Many of the orchids they grow occur in the wild as epiphytes, lithophytes, or terrestriphytes, i.e. they grow on or attached to other surfaces but only the terrestriphytes are more likely to be found growing in the ground (soil) or in the litter layer on top of the soil.

For many years we have been very successfully growing exotic terrestrial genera. Bletilla, Orchis, Pleione are some of the older genera, and in the last 10 years or so Disa uniflora hybrids as a commercial cut flower crop. Many of us grow Australian terrestrials quite successfully, mainly amongst Pterostylis, Thelymitra, Diuris and Chiloglottis.

Many of the NZ native orchid species grow as terrestrials in the ground or in the litter / organic layer above the soil.

Why don't we do the same for our often locally and nationally endangered NZ genera? One seed capsule's worth of seed put into culture would be enough to start with for any species to get it into cultivation. With large seeded genera such as Thelymitra flask culture is not always needed.

There are some people, often members of Orchid societies, growing NZ terrestrials very successfully usually in the genera Pterostylis, Thelymitra and Corybas (or any of its new names), but they are often reluctant to take credit for their achievements, or to talk about their cultivation methods, ie potting mixes and fertilisers they might use.

Apart from Microtis sp. (usually M. unifolia) that grow in a wide range of potting mixes and soil
types, are subject to all sorts of fertiliser regimens, become weeds in long term pot plants and
get a white rust like disease, most of the other NZ terrestrial orchid species don't appear to have been looked at very much for pot culture.

I've seen photos of NZ terrestrial orchids being grown very successfully in both the UK and North America.

I'm sure that in NZ there are keen gardeners, collectors and professional horticulturalists growing a number, if not most, of our terrestrial orchids quite successfully in containers.

I think it is time we encouraged those people in NZ already successfully growing NZ terrestrials in cultivation to share their knowledge so that others can learn to grow them. This would reduce the pressure on wild populations and cultivated plants would in time become more readily available.
 

Australian Growers

Several years ago my wife and I were in Adelaide at the time an ANOS show was on; we were fortunate enough to get onto a couple of the day trips that were organised to visit orchid growers in and around Adelaide. Amongst them were several that grew Australian native terrestrials very successfully (they also had permits to grow orchids rescued from development sites).

One grew plants from seed in culture without too much effort and another sowed his seed on the surface of the Casuarina (Sheoak) needle duff that he topped up all his pots with, to help reduce the growth of moss etc, and provide a seedbed. The seed was broadcast on the surface of the pot, then simply watered in and left to do its thing.

The mycorrhiza in the duff appeared to help the seed germinate well and grow strongly.
(This would be much the same as the effect on orchids that are seen growing under pines in NZ.
The success of the Iwitahi site at Taupo is in no small way due to the fact that the transplanted orchids suffer very little soil modification, and pine duff is everywhere). The resultant seedlings were pricked after two years or when the tubers were big enough to handle.
 

Growing NZ Natives

Before I retired I was employed as Technical Officer in The Fernery in Pukekura Park in New Plymouth. Part of my job was to look after the very diverse orchid collection that the Fernery is known for. The collection had been assembled over many years by George Fuller and included terrestrials from other parts of the world, but only a few from NZ.

There is a growing public interest from NZers and especially overseas visitors and tourists to see properly identified NZ orchids on display in such places as the Fernery and at shows.

In the collection there are some Australian Pterostylis spp including P. coccinea and P. nutans and Chiloglottis formicifera all growing and multiplying readily (very little water from the first sign of leaf drop to resprouting, regular seaweed based fertiliser when in growth and an open mix including pine duff). There are a few NZ Pterostylis and Corybas that did not do very well until they were put into the duff supplemented mix.

Epiphytic spp. such as Winika and Earina are very easy to grow and display, and attract a lot of attention, even when not in flower.

Although some work has been done growing NZ terrestrials from seed in sterile culture, I understand that exflasking has not always been very successful.

I'm told that standing the flasks of terrestrial orchid seedlings on the cooler floor of the growing room for a period of time prior to exflasking hardens them off so that they will survive better.
 

Growth Conditions

It is very easy to kill plants of exotic terrestrial orchid genera by being too kind;  by that I mean:

1. Too much shelter, shade and high temperatures (especially within the pots) along with increased humidity and restricted air movement.
    
2. Fancy potting mixes that are too water retentive and often break down too easily.
    
3. Too much fertiliser that is often very soluble and in forms that are not encountered by orchids growing in the wild.
    
4. Overwatering so that the root hairs on the tubers etc suffocate and drown.
    
5. Under watering by only applying enough water to keep the top layer of the potting mix damp and the bottom of the pot dry.

If we stop and take a look at the range of sites and soil types where most NZ terrestrial orchids are found in the wild, we will find that in general the soils are usually shallow, have a low nutrient status, are generally acidic and in many cases subject to dry spells, drought and sometimes seasonal flooding,

Some of my observations of growing sites in NZ are:

1. Corybas etc grow in the litter/organic or moss layer on top of wet ground or seeps and
   not in the wet ground etc. and usually under good shade.
    
2. Thelymitra often occur on dry banks especially on the top side of road cuttings and farm tracks, with the tubers developing where the topsoil and subsoil horizons meet, or where the topsoil is very thin, in cracks in the subsoil or between rocks. As these orchids appear to require good light levels to open their flowers, more open sites seem to favour them.
    
3. Pterostylis often grow under good shade in the litter layer above the bush floor soil with some of the roots but not the tubers growing down into the soil.
    
4. Orthoceras seem to like open unimproved grassland that has a light scrub cover at higher altitudes and open bush at lower levels, with the tubers growing in the soil.

Within each genus there will be exceptions to these observations. In Australia in areas where the soils are sandy or gravelly Thelymitra and Pterostylis can be found with the tubers well down into these types of soils.

In most cases the tubers develop below the roots, are annual and occur on the end of "droppers" that descend from the main root mass or from the previous year's tuber.

Droppers develop from the tips of horizontal vegetative shoots or rhizomes that arise from the previous year's tubers; these shoots or rhizomes can vary considerably in length and often have scale leaves spaced out along them. In the case of a dropper being damaged at the tip of a shoot it is possible to get a very dormant axillary bud hiding under a leaf scale to break and develop into another  shoot or dropper.   

This type of tuber reproduction and multiplication can be seen with ease if you are fortunate enough to grow or know somebody who grows Disa uniflora, a South African terrestrial orchid and its many hybrids. Here the shoots and droppers arise from the vegetative collar at the top of the previous year's tubers.
 

Growing Media

The potting mixes that I used for the Australian and NZ terrestrial genera at the Fernery and with the small collection I have at home are:

Mix 1 - below the tubers

Two parts composted fine pine bark up to 10mm grade, screened to remove the dust and small fragments up to about 1mm.

One part coarse sand/pea gravel 3-8 mm, washed to get rid of weed seeds, silt etc.

Half a part of milled sphagnum moss.

Mixed well and slightly dampened to the stage of not sticking together when squeezed into a ball.  

Mix 2 - around and above the tubers to within about 1.5 cm of the rim of the pot.

Equal parts of: screened composted pine bark and sand/pea gravel prepared as above, and screened pine duff that is prepared by collecting the duff (the layer of pine needles that is starting to rot and is just below the top layer of unrotted needles) preferably from under old pines.

Remove most of the top layer of unrotted needles and collect the next layer that will have a fair bit of fungal mycelium growing in it; don't collect the lowest layers as they will have broken down too much. Rub the duff through a 10-15mm sieve to break the needles up. Mix all 3 ingredients well and keep very slightly damp as if it is allowed to dry out too much it can be very difficult to re-wet after potting

The idea of leaving the 1.5cm gap at the top of the pot is so that the top of the pot can be topped up with some of the duff on its own as it helps to reduce the rate at which moss and liverwort develop.

As mentioned earlier the use of broken up Casuarina needles in Australia to top up pots is worth following up here if a clean supply of these needles can be found.

Mix 1 is free draining but moisture retentive below the tubers, and Mix 2 has much more air available around and above the tubers.

Most of these orchids have tubers that are in themselves quite robust, but the roots and especially the shoots and droppers and their attachment points are very fragile and easily damaged, so the plants need to be as near to fully dormant as possible to avoid damage, this timing of repotting is quite important especially if you want to separate seedlings. If the plants are already in growth the tubers are easily broken off the shoots.

Many people when potting up these types of orchids use too much force "firming" the plants in the pot; this leads to damaged, even broken roots and crushed tubers, and will allow disease in and is often the sole cause of failure. (You don't see plants of any type growing in concrete, instead they grow in the cracks and cavities in the concrete or on it, where they adapt to the constraints of the site).

If you have a slightly damp potting mix that will "flow" around the tubers and any roots that are present, then the chance of damaging the tubers and roots by gently tapping the pot on the bench as you fill the pot with mix is greatly reduced, and the mix will be finally firmed down at the first watering.
 

Fertilisers

Another way to kill these orchids is to apply highly soluble fertiliser too soon after growth commences and too often. Or have it already in the mix.

If you are repotting these plants when they are already in growth then the fertiliser should not be applied for at least one week after repotting. This will allow any damaged or broken roots to heal or start regrowing and reduce the possibility of fungal root infections becoming established.

The liquid fertilisers I used were seaweed based and used in the cut flower and pot plant industries, so have added potash to stimulate flower initiation and help the plants with disease resistance. This was applied once a week at about a quarter the rate for pot plants, at growth initiation and three times a week when in full growth until after flowering when it would go back to twice a week until the first signs of dormancy appear.   

The potassium source should be Potassium sulphate, not Potassium chloride as orchids don't generally like chloride ions.

Those pots that were left too late to repot or were not to be repotted were given a light dusting of Dolomite as growth commenced.

Having seen the seedling growth and development in Australia, in pots with a surface layer of duff,
I think it is well worth trying here, with the most important thing being to gently water the seeds into the surface of the duff and not try to cover them with the application of a further thin layer of duff.

Large seeded spp. such as Thelymitra lend themselves well to this technique, but I think it could be applied to many other genera.

Corybas and Pterostylis are kept under shade and the Thelymitra are grown in full sun.
  

Conclusion

I strongly support the concept of "conservation by propagation and distribution" and not locking rare plants up behind barbed wire etc, as this encourages greed and elitism, even leading to great losses of wild plants because of their artificially inflated "value".