9.4.26 How to grow orchid seeds with B1 fungus

Part 5: Potting up seedlings

 It is a lovely April day as I write the final part of this series. I’m hoping you have at least a few jam jars of green, healthy little orchid seedlings growing in B1 agar. If it hasn’t worked out don’t be shy to drop me an e-mail and I will try to help. If it has, then you are probably thinking about how to manage them now? Let’s address that.

Actually, provided they are sealed and with a breather in the transparent lid as discussed last time, you could just leave them in the jar all the way through the coming year! Keep jars in moderate conditions always – not where they freeze during frosts or bake in bright, hot sunlight. Ideally a semi-shade location and try to avoid temperatures above 25 degrees C.

Plantlets develop 2 or 3 leaves, often brushing the lid, and a few roots but there is a natural limit to growth in the first year, and they won’t need a bigger container than the jar. Sometime in summer they decide to die-back their foliage and a small first tuber will have formed in the agar for next year. Don’t panic into thinking the plant has died – it hasn’t. Probably not, anyway!

After dormancy a Dactylorhiza jar can be stored in a cool, frost-free place until the new shoot emerges next late-winter or early-spring. Wintergreens like Anacamptis morio develop the new green shoot in autumn, sometimes as early as the end of August, in response to the night temperatures becoming colder at that time. So check jars for new shoots emerging as they will need some light.

It is good to remember the plantlets really need to be exposed to outdoor changing seasons and day-night temperature cycles because that is what triggers their growth stages. I always get jars or pots out of the house and into a shady, frost-free greenhouse location as soon as possible. They are then in tune with the seasons while still protected from pests and extreme conditions.

To pot plantlets into soil or not to pot? -  that is the question. Mostly I have potted-up at this time and it is still my preferred option. But there are pros and cons with both ways. If you keep them in jars do observe their condition regularly. They shouldn’t dry out but if they do you can add a little de-ionised water. If the agar and fungus continues relatively unchanged, then fine. If it gets contaminated with weird and wonderful microbes and becomes a colourful or liquifying yukky mess then the plantlets will probably soon die. If that is developing then pot-up into soil, as detailed below, before it is too late.

Potting-up plantlets into soil is very easy. Have your flower pot ready, filled nearly full with moistened soil. Take the lid off the jar and, using a teaspoon, gouge out a blob of agar containing an orchid. Be careful to dig below any roots forming so you don’t damage them. Make a little hole in the soil and slide the agar blob plus plant into it. Pack it carefully with soil around and over the top of the agar leaving the foliage standing proud. Repeat with perhaps three or four plantlets in the same pot. Water in carefully, cleaning soil off the leaves. Label and place pot in a propagator or similar device in a good location, as discussed above.

The very important thing to do is to “harden off” plantlets over a week or so. This is an orthodox gardening procedure for any new seedling plant. They have been consistently humid inside their jar and they now need to slowly acclimatise to resist the dehydration of outdoor air and winds. Keep pots in a propagator tray with a lid, removing the lid for a few more hours each day over a week or so. Also water them little but often at this time. Seedling plants are very delicate in their first year and you need to cosset and protect them so that they grow for as long as possible before going dormant. Otherwise they may not have made a big enough tuber to return next year and thus perish.

All very well, but what soil to use I hear you ask? This is a big variable and I can only say lots of different recipes are out there. It should be moisture-retentive but free-draining and loose in texture so if you scrunch a handful in your palm it just falls apart. It should be fairly low in nutrients, particularly nitrogen, but be welcoming to fungal growth in having a good amount of humus.

A simple, cheap mix can work just as well as anything. For the organic component I often use about half composted bark and half peat-free multipurpose compost. For the mineral component mixtures of horticultural sand and fine horticultural grit. Use roughly equal amounts of organic and inorganic mixed together. I often top-dress the soil with fine grit as it keeps the surface dry and free of neck-rot, keeps moisture in the soil during hot weather, and discourages slugs and snails. It is not essential, however.

There are lots of other soil components and proportions you can experiment with. Orchid bark is good stuff but too expensive to use routinely. Some perlite or vermiculite or seramis is good for opening up the texture and retaining some moisture but none of these is absolutely essential. Various John Innes compost mixes are good, including Seed Compost and No. 1 for low nutrient content. Some garden soil could be used but of course this will introduce weed seeds aplenty. Chopped leaves and / or shredded cardboard are becoming popular additions nowadays to provide cellulose for fungal growth.

Plantlets will gradually establish in their pots if properly hardened off and kept adequately watered especially in the first few weeks - rain water is probably best - and located in a sheltered environment. Watering doesn’t need to be heavy. Little and often is probably best. Don’t let the pots completely dry out, even in summer after the foliage dies down. Continue moistening sparingly in autumn and winter. The only time to completely stop watering is when the temperature is below about 5 degrees C, ie approaching freezing.

Pests become a problem as soon as we grow plantlets outside their jars. Slugs and snails must be kept at bay: a single chomp can wipe out a young plant, and they are particularly vulnerable in the first few weeks. Use whatever weapons you are comfortable with. Other things “happen” too – like greenfly, mice, overwatering, leaf diseases, etc – but I can only say follow conventional gardening advice on these things. Hopefully you will be fine! See also growing advice in the main website content under “Hardy orchids from seed” and “Hardy orchids in the greenhouse”.

Potted plants follow the same cycles as those in jars so locate them accordingly as the seasons change. With jars you don’t have to worry about pests or moisture levels whereas with pots you do! If you want to be really radical, consider transplanting into soil in a jar! However, we always will want to pot up into soil at some stage. It is just a matter of when.

That’s about all I can think of, and really after the first year in the green the growing conditions are pretty much the same as detailed on the web site for larger and flowering sized plants. Rarely, you can get the first flowers in the second growing season, but more usually from the third season onwards. Good luck and send me your photos of little seedling plants!

Anthony.heys@sky.com