Winter Care for Containers on Balconies and Patios

Why Pots Feel Winter More Keenly Than Borders

A plant in the ground has the whole earth as a blanket. A plant in a pot has a few centimetres of compost and a thin wall of terracotta or plastic between it and whatever the weather throws at it. That difference matters from November to March. Compost in a container freezes from the outside in, and because there is so little of it, the rootball can be solid ice within one hard night. The same small volume dries out alarmingly fast, especially on a windy balcony where rain may never reach the compost because the foliage sheds it away from the rim.

Add the freeze-thaw cycle and you have the real culprit. On a sunny January afternoon, dark pots can warm several degrees above air temperature, thawing the compost; overnight it refreezes. Roots are not built for that repeated squeezing, and damage often shows weeks later as blackened tips or a plant that fails to bud in spring. Winter container care is less about cosseting and more about steadying the extremes.

Check Moisture Little and Often

It feels counterintuitive to water in winter, but dry roots die faster than frozen ones. Evergreens such as bay, rosemary and skimmia keep losing water through their leaves whenever the temperature is above freezing, yet rainfall is easily blocked by a dense canopy or deflected by a wall. On a sheltered balcony, compost can be bone dry while the ground outside is sodden.

Push a finger two or three centimetres into the compost, or use a cheap moisture meter, during any mild spell. Water in the morning so surplus has time to drain before nightfall, using water that has stood in a can overnight so it is not shockingly cold. If a pot is frozen solid, leave it alone - pouring water onto a block of ice simply creates a puddle that will refreeze around the crown.

• Water only when the top few centimetres are dry, not on a fixed schedule.
• Give a proper soak and let it drain rather than a daily trickle.
• Group pots together so they shelter one another and share humidity.

Insulate the Roots, Not Just the Tops

The roots are the part you are protecting, and they sit closest to the cold. Wrap the outside of the pot with bubble wrap, hessian or a couple of layers of old blanket, tied with twine, and stand it on pot feet, bricks or a wooden batten so it is lifted clear of the freezing slab. A raised pot loses far less heat downwards and drains properly after rain.

For vulnerable specimens - young plants, tender evergreens in their first winter, anything in a small pot - push a layer of bark chippings, straw or dry leaves over the compost, keeping it clear of the stems to avoid rot. Terracotta is porous and prone to cracking when wet compost freezes, so slip it inside a slightly larger plastic pot or move the best pots to a sheltered corner. A south or west-facing wall releases stored warmth overnight and can be two or three degrees kinder than an exposed corner.

Deal With Standing Water

Water is the quiet killer of winter containers. A saucer left under a pot fills, freezes, and then holds the base of the rootball in ice for days. Empty saucers and trays after every wet spell, and tip out water collected behind a balcony rail or in the folds of a tarpaulin.

Check that drainage holes are not blocked by compacted compost or circling roots. A pot with no holes is a decorative sleeve rather than a container, so use it as an outer shell with a properly drained pot inside and empty the gap after rain. Standing water also waterlogs the compost, and roots that are wet and cold rot far more readily than roots that are merely cold.

Protect the Top Growth, Gently

Frost-hardy does not mean frost-proof, and a plant that shrugs off a hard frost in a border may struggle in a pot that has chilled through. Move pots into the lee of a wall or under an overhang if you can. For evergreens such as bay, choisya and photinia, a loose wrap of horticultural fleece keeps the worst of the wind off the leaves; leave the top open on mild days so the plant does not sweat.

Avoid cutting back frosted growth midwinter. Blackened leaves look sorry, but they shield the living tissue beneath. Wait until the risk of hard frost has passed, then trim to healthy growth. Hold off on feeding too: a flush of soft new growth in January is a gift to the next cold snap.

Frost-Hardy Plants That Earn Their Place

If you are planting up pots for winter, choose plants that cope well in the same small volume of compost. Good candidates for UK balconies and patios include:

• Skimmia - evergreen, happy in shade, with red buds that hold colour all winter.
• Hellebores - tough, long-lived, flowering when little else dares.
• Winter heathers - low, wind-tolerant and generous with flower from December onwards.
• Ivy and euonymus - reliable evergreens for trailing over an edge.
• Bay and rosemary - useful and aromatic, though both appreciate shelter and a dry root run.
• Cyclamen and winter pansies - cheerful fillers that bounce back from a light frosting.

Keep the compost gritty rather than rich, water sparingly and consistently, and check the pots after every sharp night. A little attention now means containers that reach spring with roots intact and leaves ready to grow.