In this section we consider two very different approaches to growing from seed: the familiar way of sowing or scattering into a suitable soil, and the less familiar way of germinating and growing them on nutrient media under laboratory conditions.

 

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Orchid seed structure and germination

Hardy orchids occur in nature in self-sustaining colonies of plants that have grown almost exclusively from seed. Vegetative reproduction occurs only to a minor degree and results in occasional clumps within a broad spread of individual plants. Clearly, the natural seed scattering of dehiscence succeeds in the wild but it is quite difficult to make it happen artificially, in gardens. Sowing seed in commercial composts or in garden soils does not usually work unless you are very lucky. It is necessary to have certain uncommon fungal species established in the soil in a mycorrhiza, ie an interlinked partnership between the fungal mycelium and plant roots.

 

The reason orchid seeds need a beneficial fungus is because they are tiny and have no extra food reserves. Each seed can only just be seen with the naked eye. The structure is the same in all cases: a living multicellular embryo is enclosed in a protective wrapping of dead cells called the testa. Germination starts when the embryo imbibes water and the cells divide and grow into a protocorm. The protocorm is a white mass only a few millimetres across and with projecting root hairs (rhizoids). This is as far as it can get alone, as it runs out of nutrients and dies. However, in nature, specific soil fungi invade the germinating embryo at a very early stage and a symbiotic or mutualistic relationship is formed that supports the protocorm. Thus it can grow into a small green-leaved seedling and beyond into a mature plant. It is assumed that in the wild all (or nearly all) orchids need a beneficial fungus, at least in the germination stage.

 

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Laboratory seed growing

Within the last hundred years botanists and enthusiastic amateurs have developed ways of helping orchid seeds to grow in laboratory conditions. There are essentially two main approaches:

 

The Symbiotic method cultures a particular species of beneficial fungus on a medium that has nutrients but is not sugary. The fungus grows strongly and contaminating bacteria are suppressed. Orchid seeds are added and their growth is stimulated by the fungus.

 

The Asymbiotic method incubates seeds on a sugary medium that supplies all the orchid’s nutrient requirements in a soluble and absorbable form. No fungus is involved. Crucially this has to be done in completely sterile conditions, otherwise bacteria rapidly overwhelm the medium.

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Symbiotic orchid seed growing

I use the Symbiotic method almost exclusively. Seeds are sown from late August to early December to allow time for germination before winter. I work inside a home-made Perspex (ie transparent) cabinet that protects the work from above and provides a “fairly sterile" environment, or more truthfully an extremely clean but not totally sterile environment. The nutrient medium is a 5.0 g/L agar gel in tap water, with finely blended and sieved porridge oats at 3.5 g/L, and vitamins in the form of dissolved Marmite at approximately 0.1 g/L. This mixture is sterilised in a pressure cooker for 20 minutes then poured into Petri dishes and allowed to set.

 

The orchid seeds are surface-sterilised in a 10% by volume diluted household bleach solution for 20 minutes. To remove the bleach they are then rinsed in sterilised water and drained, before being re-suspended again in fresh sterilised water. Bleaching prevents microbes on the seed surfaces from transferring to the medium but does not kill the seed embryo. Seeds are then poured out onto the medium in the Petri dish.

 

Finally the medium is inoculated with the fungus. This can be a cube of agar taken from another culture of the fungus, or better still by adding an orchid protocorm from another Petri dish. The fungus is transferred within the protocorm. The Petris are labelled, sealed, and stored in the dark at room temperature.

 

The fungus grows out to cover the Petri in about 10 days. Within about 3 weeks the first stage of germination can be seen under the microscope as swollen embryos. After about 8 to 12 weeks they have grown into visible hairy white protocorms. When the protocorms reach about 4mm I transfer them with sterilised forceps to a Petri dish of fresh medium. This “thinning out” helps the fungus and orchid to keep growing strongly.

 

After 2 more weeks growth the Petri is transferred to a fridge and stored in the dark for at least 6 weeks. This gives the plant a winter, or vernalisation period, which can be necessary to trigger developmental stages in the annual growth cycle. The fridge is reliably cold, but there is no risk of the protocorms actually freezing.

 

After removal from the fridge I transfer protocorms onto fresh medium again, but now in jam jars so the shoots have room to grow upwards. The jars are incubated in the light of an indoor window ledge – north facing so that they don’t get overexposed. The first shoot turns green and develops into a leaf or two. If all goes well the orchid is, by mid to late spring, a healthy, green plantlet with the first roots developing.

 

At this stage they can be left in the jar to grow maximally then become dormant over summer, and resume growing next spring. More usually, though, I prefer to pot them into compost and transfer to the greenhouse. The composts are as described for greenhouse growing of orchids. I often plant 2 to 4 plantlets together in a single 11 cm pot. Alternatively they can be grown in greater numbers in a seed tray or pan. A teaspoon is useful to scoop the plantlet out of the jar along with a generous chunk of agar that will contain fungus. Be careful not to damage any developing roots. The chunk is tipped into a small hole in the top of the compost. Gently cover with fine grit up to the base of the stem and water in.

 

The newly exposed leaves are initially very delicate and prone to dessication. Harden them off by keeping the pots under a propagator lid for a week or so, gradually increasing time with the lid removed. Water them little but often so they retain a humid atmosphere early on. After hardening off plantlets can be treated in the same way as more mature orchids in the greenhouse, but remember they are generally more delicate in their first year. Avoid any extreme conditions. Keep them green and growing as long as you can before they eventually die back in high summer. With luck they will have formed their first small tuber for next year!

 

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Fungi for symbiotic orchid seed growing

A small number of fungal species cultured in the laboratory have proved capable of supporting germination of hardy orchid seeds and enabling them to grow into mature plants. Usually they have been isolated from orchid roots or sometimes from orchid seed packets buried in native soil. Unfortunately many apparently useful fungi seem to lose their orchid capability quickly when grown in vitro. Still more fungi are identified but cannot be made to grow in vitro.

 

The most successful fungi in use for orchid germination are from the Ceratobasidium genus. The so-called “B1” strain is a Ceratobasidium first isolated by Jim Hill (1997) and in active use by many hardy orchid growers in the U.K. – see my article about the identification of B1 in the Journal of the Hardy Orchid Society (H.O.S.). Closely related strains in this genus are often found to have this ability. They are quite easy to maintain in culture in vitro. B1 is the fungus that I generally use. It can be obtained from the H.O.S. via their fungus bank. There are also two other fungi in the bank – “A36” and “Q414” They may work for a slightly different range of orchid species to B1, but on the whole my experience is that they are less effective.

 

B1 is capable of growing probably all species of Dactylorhiza, including D. viridis, many Anacamptis (eg A. morio, A. laxiflora etc, but not A. pyramidalis), and a few species in other genera such as Herminium monorchis, Goodyera repens, Spiranthes spiralis. Possibly also some Serapias and Gymnadenia species. It can be cultured easily on the oats medium described above. B1 is best stored for the long term at a cool room temperature in the dark. Fridge storage is not necessary, and frozen storage should be avoided.

 

 

Asymbiotic orchid seed growing

I have only used this approach occasionally, so will give just a brief overview. As mentioned above, it is vital to maintain completely sterile conditions otherwise contamination by bacterial and fungal spores rapidly overwhelms the growth medium. To this end it is much easier to do the work inside a laminar flow cabinet where the air flow is sterile. However, this is a large item of professional laboratory equipment, and expensive to obtain. It is possible, though, to work without it; for example by attaching a domestic air purifier with a HEPA filter to your home made cabinet, or simply by refining and perfecting your aseptic handling techniques.

 

Many types of nutrient agar medium have been described. These include: Murashige & Skoog, Phytamax, the TGZ range, the H.O.S.’s own mix (a modified Malmgren’s medium), even diluted Maxicrop seaweed fertiliser, and there are plenty more. The main components are: agar for gelling, various dilute mineral salts and trace metals that are essential for plant growth and buffering of pH, sucrose to supply energy, amino acids, plant hormones and vitamins, and often a small amount of an organic additive such as pineapple juice, banana, swede or coconut milk etc. Not all of these are essential.

 

Some activated charcoal is usually added as this is believed to adsorb potentially harmful waste products of seedling growth. Deionised water (eg car battery water) is safest to use rather than tap water or rain water. It is best to test the final pH of the medium, and adjust to around 5.7 if necessary, for successful growth.

 

The medium is sterilised in a pressure cooker for 15 to 20 minutes before being poured into the growing container (which must be completely sterile) and allowed to set. Flasks of some kind, e.g. jam or honey jars, are used rather than Petri dishes as they are easier to keep sterile and do not become outgrown so quickly. Each jar typically contains about 50mL of medium. It is best to make the jars 2 weeks before adding seeds and avoid using those where contamination has developed.

 

For sowing, orchid seeds are surface sterilised with diluted bleach as above, and ideally rinsed one or two times with sterile deionised water. The rinsing should be minimised though, as more processing steps cause more opportunities for contamination. Seeds are then sown into the jar on the agar surface. Various devices can be used for sowing. I favour a plastic syringe without a needle for sterilisation, rinsing, and sowing. Jars are sealed, labelled and incubated initially in the dark.

 

Germination varies from rapid to very slow depending on the species, and it may require a cold period in the fridge at some point. Transfer of protocorms or seedling to fresh medium is usually needed at various stages, all the while avoiding contamination. A further complication is that the flask may need a “breather” device as the seedlings get larger to allow gaseous exchanges but without allowing microbes to get in. Protocorms are grown on to become small green plantlets that eventually can be potted up, as in the symbiotic method. During potting it is essential to wash away all traces of the sugary nutrient medium from the plantlets.

 

There are pros and cons when comparing symbiotic and asymbiotic methods. There are plenty of “challenges” with the asymbiotic route. It is hard to break the dormancy of the seeds into germination, growth is relatively slow, contamination is a constant threat, and weaning into compost is a tricky stage. Many plants can be lost at this time as they don’t have protection from symbiotic fungus in their new, non-sterile environment. Overall, it is a much more exacting procedure.

 

However, asymbiotics have the big advantage that they can be applied to all hardy orchid species, not just a selection of them.  Indeed it is used on an industrial scale to grow the tropical orchid species and hybrids that we see in garden centres and supermarkets around the globe. The big limitation of symbiotics is that the useful fungi we have only germinate some of the hardy orchid species. There are plenty of orchids we can’t grow reliably (or at all) with the symbiotic method.

 

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Seed scattering

What can the hardy orchid lover do if they don’t want to try the laboratory way of growing seeds? Despite what I have said above about seed scattering, it can be a fruitful approach if done in the right ground. Commercial composts and typical soils of garden borders are not likely to work, due to the high fertility levels and lack of symbiotic fungi.

 

Instead hardy orchid seed can be scattered over areas that are being managed as meadows. A good method is to mix seed thoroughly with a few handfuls of damp sand and scatter this as thinly as possible by hand. Water it in to make sure the seed washes down into the ground and can’t blow away. A good time to do this is in late August, after the meadow has been cut and the cuttings removed. This is the time when orchid seeds in nature would have fallen on the area from the dehisced seed pods of wild plants.

 

Established wildflower meadows often do support orchid growth. Newly-made ones seem to acquire the ability increasingly the more years the area is managed as a meadow. An unfertilised, untreated lawn can also be suitable provided you are willing to not to cut it at all in spring and early summer.

 

Much patience is required – it may not work, but even if it does it will probably take at least 3 years before you can detect the presence of orchid leaves. However some landowners with just the right soil have amazing results. Probably the best example of this is Dave Trudgill’s meadow in Perthshire (see Further Information) where his seed scattering technique has produced 14 different flowering orchid species  – be aware, though, this represents the pinnacle!

 

The best species to try would probably include A. pyramidalis, D. fuchsii or D. maculata, A. morio, O. apifera, N. ovata, and S. spiralis.

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