Evergreen ferns earn their place in British shade gardens by doing something most perennials cannot: they hold their shape through the darkest months. A hart's tongue fern, a soft shield fern or a clump of Polypodium will keep a border looking furnished in January when everything else has collapsed. But those same fronds are the plant's weak point. Cold wind strips moisture from them faster than the roots can replace it, and the damage often shows up weeks later as brown, papery tips. A little forethought in autumn and a bit of restraint in winter will carry them through to spring in good order.

Why Cold Winds Cause More Harm Than Frost Alone

Frost alone is rarely the killer. Most evergreen ferns grown in Britain are perfectly hardy in a cold snap, provided they are dormant and the roots are not sitting in a swamp. The trouble comes from the combination of wind, cold and dry air.

Evergreen fronds keep transpiring all winter, losing water vapour through their surfaces. In normal conditions the roots draw up replacements from the soil. When the ground is frozen solid, or when a drying easterly wind is pulling moisture out of the leaves faster than the roots can manage, that supply line simply stops. The result is desiccation — the technical term for a plant drying out while standing in wet soil. Fronds go crisp at the edges, then curl and blacken.

There is a second, sneakier problem. A frond that thaws in weak winter sunshine and then refreezes at dusk suffers cell damage each time it cycles. Ferns in exposed, sunny, windy positions take far more of this punishment than those in steady shade.

Choose and Improve a Sheltered Position

When siting evergreen ferns, think about what stands between the plant and the prevailing wind. In most of the UK that means a westerly or south-westerly airstream, with punishing easterlies in late winter and early spring.

• Use existing structure. A hedge, a fence panel, a shed wall or a mature shrub all break wind effectively. Even a low barrier helps, because the most damaging gusts are those that hit at frond height.
• Aim for dappled or partial shade. North and east-facing borders suit most evergreen ferns, as do the shaded sides of walls and fences. Deep, dry shade under a conifer is a different challenge entirely.
• Avoid frost pockets. The bottom of a slope, a hollow in the lawn and the far end of a walled garden all collect cold air that pools and lingers. Move ferns up the slope if you can.
• Be wary of warm south-facing walls. They encourage winter growth that is then caught out by a hard frost, and the soil at their base dries out quickly.

If you have no natural shelter, plant a loose, open windbreak rather than a solid one. A permeable barrier filters the wind and creates a calmer pocket; a solid one simply pushes the turbulence over the top and dumps it behind.

Protecting Ferns in Pots and Containers

Ferns in containers are far more vulnerable than those in the ground. The entire rootball can freeze through, and a pot standing in the open offers no shelter whatsoever to the fronds.

• Move pots into shelter. An unheated greenhouse, cold frame, porch or the lee of a house wall will do. Even shifting a pot two metres closer to the building makes a measurable difference.
• Raise them off the ground. Pot feet or a couple of bricks prevent waterlogging and stop the base of the pot freezing into the paving.
• Group pots together. Clustering containers creates its own microclimate, with the plants sheltering one another.
• Insulate the rootball. Wrap the pot in bubble wrap, hessian or an old woolly blanket, and top the compost with a layer of bark chips or leafmould. Leave the crown itself uncovered so air can circulate.
• Use a larger pot than you think you need. A generous volume of compost takes far longer to freeze solid than a small one.

Water Through Dry Spells, Even in Winter

This is the advice most often ignored, and it is often what separates a pristine fern from a scorched one. Evergreen ferns under the eaves of a house, beneath a dense evergreen canopy or in a sheltered porch may receive almost no rain at all.

Check the compost or the top few centimetres of soil every fortnight or so. If it is dry, water — but only when the ground is not frozen and the temperature is above freezing. Water in the morning so surplus moisture has time to drain before the evening chill. Never leave a pot standing in a saucer of icy water.

A mulch of leafmould or well-rotted bark applied in autumn helps in two ways: it holds moisture in the soil and it insulates the crown and roots from sharp temperature swings.

Resist the Secateurs Until Spring

Brown, battered fronds are tempting to tidy away in December. Please don't. Those damaged leaves are still sheltering the crown beneath them, shielding the growing point from wind, frost and sudden thaws. Cut them off and you expose the heart of the plant at the worst possible moment.

Wait until late winter or early spring, ideally around March or just as new croziers — the tight, fiddle-headed shoots — begin to unfurl from the crown. Then you can cut the old fronds back to the base in one tidy pass, or simply snap off the worst of them by hand and leave the rest to fade beneath the new growth.

Once the new fronds are up and the soil has warmed, give the plant a light mulch and a modest feed of general-purpose fertiliser or a top-dressing of compost. Evergreen ferns respond well to a slow release of nutrients in spring, and the fresh fronds will quickly conceal the remains of winter's wear.