The easiest way to propagate new plants is spore cultivation. This may sound very scientific but is in fact a fairly simple but lengthy process. Taking approximately 2-3 years for small plantlets to be produced. There are several advantages to spore propagation which include; allowing you to multiply your favourite species, propagate ferns from spore banks that may not be widely available and lastly cross ferns to produce new species.
Step 1. The first step is to collect your spores; this is best done from mid-late summer. The spores can be found on the underside of mature fronds or fertile fronds. If you are unsure try a few different fronds from around the plant. It doesn’t hurt established ferns to remove a section of a frond although it may ruin the appearance of the fern so ask before ripping apart your neighbour’s prize plant.
Spores are usually ripe when they turn a deep brown/black colour, often ripe and unripe spores can be found on the same frond as they ripen in sequence from the tip to the base. So to maximise your chances of getting ripe spore take several pinna from different parts of the same frond. Once the spores have been collect we put them in clearly labelled envelopes and place them in the airing cupboard for 3-5 days to allow the spores to shed.
Step 2. The next stage is to prepare your container and planting medium. Do this at least 24 hours in advance of sowing the spore. Spore can be sown in a number of containers, 9cm plant pots make good containers. But anything that can be sealed airtight should work. Once you have selected your container make sure it is clean as dirt may carry other plant seeds or fungal spores. Fill your container with your medium. It is good to experiment with mixes of compost to see which work best for you. I often experiment with different mixtures but have found coarse ericaceous compost works best for me.
Once you have filled your container with the mixture this planting medium needs to be sterilized. The easiest way to do this is to pour boiling water over the entire surface of the compost ensuring all compost has been scalded. This process kills of any competing spores that may be present in the medium. When using 9cm pots I then place the sterilised pots into medium zip seal freezer bags, but anything that will seal the pot is fine.
Step 3. Now the spores have been collected and the planting medium has been prepared, you can prepare to sow the spore. It is best to do this in a still environment and to change locations between sowings of different spores; otherwise unwanted cross contamination can occur.
One of the advantages of using an envelope to dry the spores, is it can also be used to clean the spores (although this process is not essential). Tap the contents of the envelope into one corner and tear this corner off to create a 5-10cm equilateral triangle. At this stage remove any large pieces of debris by hand, gently tapping it to remove any spores on this.
The torn off triangle will create a funnel to pore the remaining spores and debris down. Angle the funnel at 45° and very gently tap the bottom, you will see the brown debris start to fall off, leaving behind a very fine layer of brown dust, these are the spores!
Step 4. Once the spores have been cleaned they are ready to sow. If there is one piece of advice I can give you is too sow the spores thinly! I cannot emphasize how important to do this. The more spores you sow the more competition there is, thus the plants will crowd themselves out and growth will be stunted with many prothalus (first stage of growth) dying. I would recommend no more than a small pinch of spores in a 9cm pot.
Once the spores have been sown label them all clearly to avoid confusion when planting on. Then leave the sowing’s in good light but not direct light, they can be left untouched for the next 6-9 months. If spores are sown midsummer a green film may appear on the top of the compost after 2-3 months. With some spores from Cyathea cooperi a green film may appear after just a few weeks! For some spores it may a year or longer for the first signs of life to appear so be patient. There should be no need to water the spores as the sealed bag/container should not lose water. However if after 9-12 months you see no activity you can spray with a small amount of fresh rain water to act as a catalyst.
Step 5. Once plantlets have developed several true fronds the plants can be divided into liners or small pots. Remember to cover the pricked out plants to seal the moisture in. At this stage the small plantlets are very sensitive to changes in humidity. These small plantlets are usually not ready to be pricked off into individual pots until they have developed several true fronds and are approximately 5cm in height. When the individual plants have established several more sets of fronds in the sealed bag and have reached 10cm you can start hardening them off.
When hardening off young plants the simplest way to avoid sudden humidity changes is to slowly open the freezer bag or remove the covering and gradually expose pots over several weeks. Ensure during this process that you keep the plants well watered with rain water.
There is always the urge to plant on all the young plants; unless the species is very rare or you have very few plants germinate only plant on the strongest you don’t want to keep weak plants. I plant young plants out into plugs in ericaceous compost mixed with one part horticultural sand. This encourages good root growth and helps prevent the plants from rooting if they get to wet. After about a year or growing season the plants can be potted on.