Why pots suffer more than borders

A plant in the ground has a huge reservoir of soil around its roots, and the earth below the frost line stays surprisingly steady through the worst of winter. A plant in a pot has none of that protection. Compost in a container can freeze from every direction, including up through the base, and the whole root ball may sit below zero for days on end. Add our national speciality — weeks of cold, drizzling rain — and you have the second problem: waterlogged compost. In my experience roots in pots rot from winter wet far more often than they are killed by frost, and by the time yellowing leaves appear in March the damage is long done.

Terracotta has a vulnerability all of its own. It is porous, so water held in the clay expands as it freezes, and a pot that has shrugged off ten summers can flake, crack or split clean in half during a single sharp frost.

Move containers to sheltered walls

The single most effective thing you can do costs nothing but a bit of lifting. Move pots against a house wall, ideally a south- or west-facing one. Brickwork and masonry soak up warmth during the day and release it slowly overnight, keeping the compost a degree or two above the temperature of an exposed corner. A wall or dense hedge also cuts wind, which is what dries out evergreen foliage and chills root balls far faster than still air.

Group pots together, shoulder to shoulder, so they insulate one another and present less surface area to the cold. Standing them on pot feet, bricks or timber battens lifts them clear of freezing, sodden paving and keeps drainage holes flowing. Avoid dragging heavy containers — lift by the rim, never by the stem, and use a sack trolley or a second pair of hands for anything above about 30cm across. Big pots are worth planning for in autumn, before the compost freezes solid and the whole thing becomes immovable.

Wrap the pot, not just the plant

Insulating the container itself is the part most gardeners skip, yet it protects the roots where it matters. Wrap the outside of the pot with two or three layers of bubble wrap, then cover that with hessian, old sacking or a length of fleece tied with twine if you want it to look less like a parcel. Leave the base and the drainage holes clear so water can still escape. Terracotta and thin glazed pots deserve this treatment most; thick frost-proof stoneware and timber containers need it less.

On top of the compost, add a mulch of bark chips, straw, leafmould or well-rotted manure, a good 5cm deep, but keep it clear of the stems so it does not hold damp against the crown. For tender foliage, drape horticultural fleece over the plant and remove it on mild days so the leaves can breathe.

• Wrap the pot, not just the crown — roots are the priority.
• Never tie plastic bags around plants; they trap condensation and encourage rot.
• Where you can, move empty terracotta pots into a shed or garage for winter.
• Bring tender specimens under cover early rather than rescuing them after the first frost.

Water less, drain more

Overwatering is the winter killer. From October onwards, most container plants need very little, and growth has slowed to a crawl. Check the compost a few centimetres down with your finger before reaching for the can, and water sparingly, mid-morning, on a mild day so the surplus has time to drain before nightfall.

Always remove saucers through winter. A pot standing in an inch of rainwater has roots sitting in cold soup, which is a recipe for root rot. If a pot must stay out in the open, tilt it very slightly so rain runs off, or tuck it under the eaves. Do not feed — fertiliser encourages soft, sappy growth that the first hard frost will blacken overnight.

One exception is worth remembering: evergreens in pots, such as bay, olive and choisya, keep losing moisture through their leaves on windy days. If the compost has been dry for a fortnight, a small drink on a mild morning will do far more good than harm.

Tender plants that earn their fuss

Some plants repay a little extra effort. Pelargoniums and fuchsias are happiest moved into a cool, bright porch, conservatory or unheated garage; take cuttings in late summer as insurance. Citrus need light as well as shelter, so a conservatory suits them better than a dark shed. Bay and olive are reasonably hardy but detest wet roots, so shelter them against a wall and keep them on the dry side.

Tree ferns benefit from straw packed into the crown and fleece around the trunk. Agapanthus, cannas, aeoniums and cordylines all survive better against a warm wall with a dry mulch over the compost. Dahlias are easiest lifted altogether and stored as tubers in barely moist compost in a frost-free place.

A short winter pot checklist

• Move pots to a sheltered wall and group them together before hard frosts arrive.
• Raise containers on feet or bricks and clear blocked drainage holes.
• Wrap terracotta and thin-walled pots in bubble wrap and hessian.
• Mulch the compost surface, keeping it away from stems.
• Remove saucers and cut watering right back.
• Fleece tender foliage overnight; uncover on mild days.
• Check pots after storms and re-tie anything that has shifted.

Do these few jobs on a dry, mild afternoon and your containers will come through winter with healthy roots and undamaged pots, ready to grow away strongly next spring.