Why grow ferns from bulbils and offsets?

Ferns are among the most rewarding plants for a shady British garden. They bring texture, movement and a sense of ancient woodland to even the dampest corner. Most gardeners know they can divide established clumps in spring, but there is another, more delicate pleasure: raising new plants from the tiny fernlets that some species produce on their own fronds. These are called bulbils, and they are essentially miniature ferns complete with tiny roots and fronds, waiting for a chance to grow. Other ferns produce offsets — small daughter plants that emerge from the base or from creeping rhizomes. Both methods are simple, satisfying and cost nothing but a little patience.

Which ferns produce bulbils and offsets?

Not every fern does this, so it pays to know your plants. The classic bulbil producer is the hen and chicken fern, Asplenium bulbiferum. Its arching fronds carry dozens of tiny plantlets along the midrib. This species is tender in most of the UK, so it is usually grown in a frost-free greenhouse, conservatory or as a houseplant. For a hardy garden alternative, look for Polystichum setiferum proliferum, a soft shield fern that produces bulbils on the rachis — the central stem of each frond. Another hardy option is Woodwardia radicans, the chain fern, which forms bulbils at the very tips of its fronds, often bending down to root where they touch soil.

Offsets are more common. Many ferns with creeping or clump-forming rhizomes — such as Polypodium vulgare, Blechnum spicant and various Asplenium species — will produce small plantlets at the edge of the crown. These are already rooted and simply need separating. In both cases, the principle is the same: detach the young fern, pot it in moist compost, and give it the humid, shaded conditions it needs to establish.

Detaching bulbils without damaging the parent

Timing matters. Wait until the bulbils have developed at least two small fronds and you can see tiny roots at their base. This usually happens in late summer or early autumn, when the parent frond is fully mature. If you detach too early, the bulbil may not survive. Use a sharp, clean knife or a pair of fine tweezers. Work over a sheet of newspaper to catch any fallen plantlets.

• Hold the parent frond gently with one hand. With the other, slide the knife under the bulbil where it joins the midrib.
• Cut cleanly, taking a tiny sliver of parent tissue if possible — this reduces shock. Do not tear the main frond.
• If a bulbil has already dropped off naturally, simply pick it up and pot it. These often root readily.
• For offsets, use a knife to sever the connecting rhizome or stolon. Make sure each offset has its own roots and a growing point.

Some bulbils will already have small roots dangling. Handle them by the frond, never by the roots, and keep them moist while you work. If you cannot pot them immediately, wrap them in damp kitchen paper for a few hours.

Potting up: compost, containers and humidity

Use small pots — 7cm is ideal for bulbils, 9cm for offsets — with a free-draining, moisture-retentive mix. A good homemade blend is two parts peat-free multipurpose compost, one part perlite or horticultural grit, and one part leafmould or coir. This gives the fine roots something to grip while allowing excess water to drain. Fill the pot, make a hole with a dibber, and settle the roots in gently. Firm the compost around the base, but do not bury the crown.

Water with a fine rose until the compost is evenly moist, then place the pot in a propagator or cover it with a clear plastic bag. Keep it out of direct sun and aim for a temperature of 15–20°C. Vent the cover every few days to prevent mould. The compost should never dry out completely, but it must not be waterlogged. Roots usually appear within four to eight weeks. Once you see roots emerging from the drainage holes, the young fern is ready to be potted on.

Caring for offsets and growing them on

Offsets are more robust than bulbils, but they still need a gentle start. After potting, keep them in a shaded, humid spot for a few weeks. A cold frame or a sheltered north-facing wall is ideal. Water regularly, but let the surface of the compost dry slightly between waterings. Once new fronds unfurl, you can begin to acclimatise them to lower humidity by opening the propagator vent or removing the plastic bag for longer periods each day.

Hardy species such as Polystichum proliferum and Woodwardia radicans can be planted out after a full growing season. Choose a spot with dappled shade and humus-rich, well-drained soil. Add leafmould or garden compost to the planting hole, and mulch around the crown. Tender ferns like Asplenium bulbiferum should be overwintered indoors or in a frost-free greenhouse. Keep them just moist, not wet, during the darker months.

• Slugs and snails love young fern fronds. Use barriers or evening patrols.
• Vine weevil can damage roots in pots. Check for white grubs when repotting.
• Scale insects may appear on tender species indoors. Wipe them off with a damp cloth.

With a little care, your bulbils and offsets will grow into sturdy plants. It is a slow but deeply rewarding process — and you will soon have spare ferns to plant in those bare shady corners or share with fellow gardeners.