Winter Protection for Tender Garden Plants

Read the Forecast, Not the Calendar

British winters are rarely uniform. A garden in a sheltered Cornish valley may sail through in a mild, damp fug, while the same plants in an exposed Midlands plot or a frost pocket in the Pennines will be tested hard by November. The trick is to work to your own garden's conditions rather than a fixed date, and to finish the job before the first proper frost, not in the middle of it.

Start watching the forecast from early October. As soon as a night of around -2°C or lower is predicted, and the soil still holds some autumn warmth, get moving. Plants that are tucked up while the ground is still relatively warm settle better than those wrapped in a panic in January. Priority order: tender plants in containers first, then architectural exotics, then borderline hardy perennials in the open ground.

Get the Pots Off the Ground and Under Cover

Roots in containers freeze far harder and far faster than roots in open soil, because the compost is exposed on all sides. A pot that has frozen solid can kill a plant outright, even one that would shrug off the same temperature in the border.

• Move the most tender pots into a greenhouse, cold frame, unheated garage, porch or conservatory. Even an unheated shed is a few degrees kinder than the open garden.
• Where space is short, shift pots tight against a south- or west-facing house wall. That single metre of shelter can make the difference.
• Raise every pot onto feet, bricks or slates so it never sits in standing water. Waterlogged compost in winter kills more plants than cold alone.
• Group pots together and wrap the outer containers with bubble wrap, hessian or an old blanket. Insulate the pot, not the plant's foliage.
• Terracotta and glazed pots crack in hard frost. Wrap them or empty them and store them dry.

Cut watering right back, but do not let compost turn to dust. Evergreens in pots keep transpiring through winter, so give them a modest drink during any mild, dry spell.

Wrap the Tree Ferns and Cordylines

Dicksonia antarctica has one vulnerable point: the crown, where the new fronds emerge. The trunk is surprisingly tough, but a wet, frozen crown will rot it from the top down.

Once the fronds have been blackened by the first frost, cut them back to about 15cm from the trunk, or simply tie them upright into a soft bundle with twine. Pack the crown generously with dry straw or crumpled newspaper, then cap it with a layer of horticultural fleece. Hold it all in place with a cage of chicken wire, tucked around the trunk and secured with twine. Wrap the trunk itself in hessian or bubble wrap for extra insurance.

Never wrap tree ferns in plastic sheeting. It traps moisture against the crown and encourages exactly the rot you are trying to prevent. Cordylines and hardy palms benefit from the same treatment: tie the foliage upwards into a column, then wrap with fleece, leaving the top slightly open so air can move.

Mulch Crowns with Straw, Bracken and Leaf Mould

For herbaceous and borderline hardy plants in the ground — agapanthus, crocosmia, penstemons, salvias, cannas, dahlias, gingers and the like — the roots and crown are what matter. Wait until the top growth has been blackened by frost, cut it back, then bury the crown under a generous blanket.

• Aim for 10–15cm of dry straw, bracken, leaf mould or bark chippings. Bracken is the traditional choice because it traps air beautifully.
• Keep the mulch clear of direct contact with woody stems, where damp material can cause rot. A collar of grit or sharp sand around the stem helps.
• Mulch only when the soil is reasonably dry and free-draining. A wet mulch on heavy clay can do more harm than good.
• Check afterwards for mice and slugs, which will happily overwinter in a warm straw bed.

Fleece, Cloches and Windbreaks

Horticultural fleece is cheap, light and effective. A double layer can buy you two or three degrees on a cold night, which is often all that stands between survival and a mushy crown. Just remember to lift fleece during mild, sunny spells to let air circulate and prevent mould.

Cloches suit alpines and small tender plants, but ventilate them on bright days. For wind, which desiccates evergreens as surely as cold, rig a temporary screen of netting or hessian on the prevailing side. Water plants thoroughly before a cold snap, too — dry roots suffer far more than moist ones.

Check Through the Winter and Be Patient in Spring

Winter is not a job you finish in one afternoon. After gales, check that wraps and fleeces are still secure and that water is not pooling in the tops of them. Replace sodden straw with fresh, dry material. Keep mulch topped up until at least mid-spring.

Above all, resist the temptation to unwrap too early. In most British gardens, a sharp frost in late April or early May does more damage than anything January throws at us. Leave protective straw in place until the middle of May in colder districts, then uncover plants gradually over a fortnight so they harden off gently. Note what came through and what did not — it is the surest guide to an easier winter next year.