Why Pots Suffer More Than Borders

Plant roots in the ground have the whole mass of the earth to insulate them. Roots in a pot have a few centimetres of compost and a thin wall of terracotta, plastic or glazed ceramic between them and whatever the winter throws at them. In an exposed garden, that difference matters enormously. A cold, clear night can freeze a small pot solid from top to bottom, while the soil just a metre away stays workable.

Add wind and winter wet and you have a triple threat. Frost damages cell walls. Wind strips moisture from evergreens that cannot replace it from frozen compost. And persistent rain turns free-draining compost into a soggy, airless block that rots roots quietly through December and January. The good news is that all three problems can be tackled with a few hours of work and materials you probably already have.

Wrap the Pot, Not the Plant

Insulating the pot itself is the single most effective thing you can do. The aim is to stop the compost freezing and thawing repeatedly, which is what heaves roots and cracks terracotta.

• Bubble wrap is cheap, effective and reusable. Wrap a double layer around the outside of the pot, from rim to base, and secure with string or tape. Do not cover the compost surface or the crowns of the plants.
• Hessian looks softer and breathes better. Sacking or hessian wrapped around a pot and tied with twine suits terracotta and looks far better in a courtyard than shiny plastic.
• Pot feet, bricks or timber battens lift pots clear of paving. This is essential, not decorative. Standing water under a pot wicks upwards and freezes, and it blocks the drainage hole.
• Group pots together in a sheltered corner, packed shoulder to shoulder. They insulate one another, and a cluster of pots creates its own still microclimate.

If you have a terracotta pot that has already cracked, retire it for the winter rather than risk losing both pot and plant.

Move Tender Plants Before the First Frost

Timing beats cleverness here. Move tender plants in before the first hard frost, usually late October to early November in most of the UK, and certainly before the first forecast of minus figures. A plant that has had a few weeks to settle under cover copes far better than one moved in a panic during a cold snap.

Priority candidates include citrus, olives, pelargoniums, fuchsias, agapanthus, tree ferns and anything you brought home from a Mediterranean-style planting scheme. A frost-free greenhouse, conservatory or bright porch is ideal. Failing that:

• Push pots against a south- or west-facing wall, which radiates stored warmth overnight.
• Use a cold frame or an unheated porch for hardy-but-not-bulletproof plants such as bays and phormiums.
• Reduce watering drastically once plants are under cover. Damp compost plus cold is far more lethal than cold alone.
• Stop feeding from autumn onwards. Soft, sappy growth produced by late feeding is the first thing to be damaged.

Evergreens under cover still need light and a little air. Do not cram them into a dark shed and forget them until March.

Drainage Is Your Winter Insurance

Winter wet kills more container plants in the UK than frost does, and it does so quietly. If water sits in a saucer or the drainage hole is blocked by a slug, roots suffocate and rot.

• Remove saucers and drip trays from outdoor pots for the winter unless the pot is under a porch roof.
• Check drainage holes are clear, and raise pots on feet so water runs away freely.
• Loosen the top few centimetres of compost with a hand fork so rain soaks in rather than running off the surface.
• Move pots under eaves or against a wall if they sit in a spot where water pools on paving.

If you garden on heavy clay, standing pots on a gravel-filled tray or a bed of pea shingle prevents the base from sitting in a puddle.

Protect Top Growth Without Suffocating It

Once pots and drainage are sorted, you can turn to foliage. Horticultural fleece draped over tender evergreens and tree fern crowns works well, but keep it off the leaves where possible by using a few stakes or a simple frame. Fleece that lies wet against foliage can cause more damage than the frost it prevents.

For tree ferns, pack the crown with dry straw or bracken and tie the fronds upwards around it. For agapanthus and other herbaceous pots, a thick mulch of bark chippings or straw over the compost surface insulates the roots, but leave a small gap around the stems so the crown does not rot.

After snow, knock heavy loads off evergreen foliage and off fleece covers promptly. A wet snowfall followed by a hard freeze can snap branches that would otherwise have come through unharmed.

A Short Midwinter Check

Winter protection is not a one-off job. Walk the garden after storms and hard frosts, and check for pots that have tipped, covers that have blown loose and compost that has frozen solid. Water sparingly on mild, bright days if compost is bone dry, particularly for evergreens under cover. A little attention in January is what gets your container displays, and your courtyard, looking full again by April.