A tree fern changes the mood of a garden. Put one in a shady corner and within a season you have a canopy of arching fronds, uncurling from tight coils in late spring like something shipped in from a rainforest. In Britain, one species does most of the work: Dicksonia antarctica, the soft tree fern from Tasmania and south-eastern Australia. Give it the right spot and a little winter attention, and a modest trunk will sit there contentedly for decades.
Choosing a tree fern and checking it over
Almost every tree fern sold in the UK is Dicksonia antarctica, and for good reason: it is the hardiest of the widely available species and the most forgiving of our damp, changeable weather. Dicksonia squarrosa from New Zealand is a decent second choice, while the faster-growing Alsophila australis (still sold as Cyathea) needs a mild, sheltered garden — Cornwall, west Wales, coastal Devon, or a warm city courtyard.
Trunks are sold as cut logs, usually 30cm to 1.5m tall. The trunk is not wood but a dense mass of fibrous roots, which is why a bare trunk can be planted and will root. Look for a firm, heavy trunk with no soft patches, and a crown that is plump and pale rather than blackened or hollow. Buy from a nursery that sources responsibly, and plant in spring if you can, so roots have the whole season to establish.
Where to plant
Site is everything. Get this right and the rest of the care is straightforward.
- Light: dappled shade is ideal, or morning sun with shade from the worst of the midday heat. Deep gloom gives sparse, leggy fronds; full sun scorches the crown and dries it out.
- Shelter: wind shreds fronds and rocks the trunk loose. A wall, fence or a backdrop of shrubs makes a real difference.
- Soil: humus-rich and moisture-retentive, but free-draining. Winter waterlogging rots trunks faster than frost does.
- Space: a mature fern can throw fronds two metres across. Leave room for it to spread.
Frost pockets — valley bottoms, north-facing slopes, heavy clay in the Midlands and north — need more protection than a warm city garden or a sheltered Cornish border.
Planting, step by step
- Dig a hole twice the width of the trunk and roughly as deep. Fork in plenty of well-rotted compost or leafmould.
- Stand the trunk in a bucket of water for an hour or two first. A dry trunk is a stressed trunk.
- Set it upright and bury the bottom 20–30cm. This steadies the trunk and gives new roots somewhere to form. Firm the soil well around it.
- Stake short and low if the trunk rocks at all, then water thoroughly.
- Mulch around the base with leafmould or bark, keeping it clear of the trunk itself.
In a pot, use a loam-based compost such as John Innes No. 2 and choose something wide and heavy enough not to blow over. Container ferns need more water and more winter protection than planted ones.
Watering and feeding through the year
The trunk behaves like a sponge, drawing moisture through its surface, and the crown needs to stay damp through the growing season. Water both. In summer, a new planting wants a good soak every day or two in dry weather; an established fern will take a weekly drenching, but a quick spray over the crown on hot mornings pays dividends.
Feed with a weak liquid seaweed or general-purpose feed, diluted to about half strength, poured into the crown and over the trunk every two or three weeks from late spring to late summer. Ease off by early autumn so the new growth hardens before the cold.
Aim to water in the morning rather than the evening. A crown that goes into a cool night wet is more likely to rot than one that dries off during the day.
Winter protection: wrapping trunks and crowns
The trunk is tougher than the crown, and it is the growing point at the top that you are really protecting. Brief dips to around -8°C are usually survivable in a sheltered garden; a long, wet freeze is not.
Start in late autumn. Cut back on watering, but do not let the trunk shrivel — a well-hydrated trunk copes with cold better than a dry one. Leave the fronds on while they are still green, then, once they brown, tie them upright over the crown like a wigwam. They make excellent insulation.
Then add a fistful of dry straw, fleece or dry leaves directly over the growing point, and hold it in place with a fleece or hessian cone. Wrap the trunk itself in hessian, fleece or a hessian-and-straw sandwich, tied loosely at intervals. Avoid sealing the trunk in plastic, which traps moisture and encourages rot — the wrapping needs to breathe.
In mild coastal or city gardens, crown protection alone is often enough. In colder inland gardens, double up and don't unwrap too early.
When to wrap and when to unwrap
Wrap when proper frosts are forecast, not before — usually late November or December in most of the UK, earlier in Scotland. Unwrap on a mild, dry day once the hardest frosts have passed, often late March or April, and do it gradually over a week rather than all at once. Keep fleece to hand: a late frost can nip fresh croziers.
Spring, summer and common problems
New croziers push up from the crown in late spring, sometimes not until June in a cold garden. Don't panic if April passes quietly. Once new fronds are unfurling, the old ones can be cut away.
- Pale, yellowing fronds in summer: usually dryness at the roots or too much sun.
- Crisp brown edges: wind or drought — check both.
- Fronds blackened after frost: cut them off. The crown may be perfectly fine.
- Soft, sunken trunk: rot from waterlogged soil or sealed winter wrapping.
- Crown mushy and dark: the growing point has died, and that trunk will not reshoot.
Getting into a rhythm
Tree ferns are slow, adding only a few centimetres of trunk a year, so the routine is gentle: unwrap and feed in spring, soak the trunk and crown through summer, leave the fronds on in autumn, wrap up before the hard frosts, and keep the crown dry and insulated until spring returns. Do that, and a single trunk can become the best thing in the garden.
Photo: Giuseppe Di Maria / Pexels
