Why grow ferns from spores?

Most of us buy ferns in pots, which is quick and perfectly sensible. But raising them from spores is one of the great slow pleasures of the shady garden. A single ripe frond can release millions of spores, so one sowing may eventually furnish a whole north-facing border, a damp corner behind the shed, or a few gifts for friends. Ferns earn their keep in the awkward places — dry shade beneath trees, the foot of a wall, a boggy patch that never dries out.

Be realistic about the timescale. From dusting spores onto compost to a pot of recognisable fronds can take anywhere from nine months to two years. The payoff is a colony of tough, long-lived plants that cost you nothing but patience.

Collecting and storing spores

Look at the underside of mature fronds in late summer and early autumn. Ripe spore cases dry to brown or rust and release a fine dust when tapped; anything green or cream is unripe and will not germinate.

• Snip a spore-bearing frond and lay it flat in a paper envelope or a folded sheet of paper.
• Label it straight away with the name and date — you will not remember later.
• Leave it in a warm, dry room for a few days so the spores drop out.
• Tilt the paper to gather the dust in one corner, fold it closed and store somewhere cool and dark.

Spores keep for a year or two, but fresh ones germinate far more readily, so sow within a few months if you can.

Sowing on sterile compost

Everything depends on cleanliness. Algae, moss and damping off all grow faster than young ferns, and there is no chemical fix at this scale.

• Use a soil-free seed compost, or a mix of compost and fine horticultural grit, in a shallow clean pot or tray with drainage holes.
• Sterilise it by pouring boiling water through the filled pot, letting it drain and cool completely. Some growers microwave damp compost for a few minutes instead.
• Tamp the surface level and water from below with cooled boiled water.
• Tap the spores thinly across the surface — a light dusting, not a carpet. Do not cover them with compost; they need light and constant moisture, not burial.
• Cover with a clear lid or a sheet of cling film. A small vent is useful for airflow.

Humidity, light and the long wait

Stand the container somewhere bright but out of direct sun, ideally between 15°C and 20°C. Sun through a sealed lid will cook the whole tray in an afternoon. Keep the compost consistently moist but never sodden; mist with cooled boiled water, or water from below if your container allows it.

Within weeks you may see a green film on the surface. This is either algae or the beginning of the interesting part. Somewhere between two and four months in, look for tiny flat green plates about the size of a lentil, often vaguely heart-shaped. These are prothalli — the independent stage of a fern's life cycle, and a genuine milestone.

Here is the tip that catches most people out: fertilisation happens in water. Mist the prothalli gently every few days so a thin film of moisture sits on them. Without that film, no new ferns will form, however healthy the green plates look.

From prothallus to proper fronds

After fertilisation, the first true fronds push out of the prothalli as tiny green specks. They look nothing like the adult plant at first — often simple and undivided — which alarms beginners. Leave them until each clump has several fronds and stands a centimetre or so high.

Prick out in small clumps rather than singly. A teaspoon is the ideal tool for lifting them without damage. Pot the clumps into small pots of free-draining compost, water them in, and keep them in a humid, shaded spot — a vented propagator or a perforated polythene bag works well. Acclimatise them over several weeks by opening the vents gradually. Grow them on away from direct sun, potting on as the roots fill each pot, and plant out in spring or autumn once they are sturdy.

Troubleshooting and good first ferns

• Green slime or algae: too wet and too bright. Lower the light, open the vents, and sow more thinly next time.
• Moss: the same causes, plus compost that was not properly sterilised.
• Nothing at all: the spores may have been old or unripe. Keep the pot for a full year before giving up — hart's tongue in particular can be glacially slow.
• Seedlings collapsing overnight: damping off. Improve airflow and use only cooled boiled water.

Easy native ferns to start with include male fern (Dryopteris filix-mas), hart's tongue fern (Asplenium scolopendrium), common polypody (Polypodium vulgare) and lady fern (Athyrium filix-femina). Maidenhair ferns and tree ferns are fussier — save those for after your first success. Keep a label in every pot, because for the first year or so they all look maddeningly alike.