Propagating ferns from spores
Spore propagation can seem highly complicated but in reality the processes are simple and success easily achieved as long as strict hygiene is observed. Very few spore-producing ferns breed true, so be prepared for some unpredictable results.
Most ferns produce spores in small heaps or lines on the undersides of the mature fronds; the royal fern, Osmunda regalis, bears its spores at the frond apex. Unripe spores tend to be pale green, turning deep brown as they ripen - in sequence from tip to stem. It is possible, in mid- to late summer to find both on a single frond.
Place a small piece of spore-bearing frond in a dry paper envelope and keep for a day or so in a warm, dry place. Any spores will then have settled in the bottom of the envelope as a dust-like brown, yellow or black powder.
Fill a 7.5cm (3in) plastic pot to within 1cm (0.75in) of the top with John Innes seed compost or a 50/50 mixture of peat and sharp sand. It is essential to surface sterilise the compost to kill any stray fungal, moss or fern spores, so place a disc of newspaper on the surface and pour boiling water onto it until the water coming from the bottom of the pot is very hot. Then cover the pot with a piece of glass or plastic and leave until the compost becomes cold.
Sprinkle the spores very thinly over the compost surface and immediately cover the pot with clear polythene or cling film, secured it in place with string or an elastic band and label. If sowing different batches, sow each in a different room to avoid cross contamination.
Place the pots in a cool, lightly shaded site for a month or two by when a green film on the compost should be visible. This will gradually form the prothalli and after a further month the first fronds will appear. When two to three fronds are visible, the sporelings can be pricked out (in clumps) into pots of sterilised compost. Enclose in a polythene bag in indirect light for a few days, as exposure to dry air can be fatal.
Mid-summer sowings may well produce true fern fronds by winter, but autumn sowings may not until the following spring. In one to two years the young ferns will be large enough to be planted out in the garden.
William Denne