Why Containers Struggle in Winter

Container plants live a tougher life than anything in the ground. Their roots sit in a small volume of compost that freezes from the outside in, and because the pot is exposed on every side, there is nowhere for them to retreat to. A plant in open soil can draw on the warmth of the earth below; a plant in a pot has only the pot.

The real damage usually comes from two things: the freeze-thaw cycle and sitting wet. Water expands as it freezes, and repeated freezing and thawing puts enormous pressure on the walls of a container. Terracotta, being porous and brittle, is especially vulnerable, and a hairline crack in January becomes a broken pot by March. Meanwhile, compost that stays saturated through the wetter months starves roots of oxygen, and in mild spells it can rot them outright. Get these two things under control and most containers will come through winter unscathed.

Raise Pots Onto Feet

The single most effective thing you can do is lift every container off the ground. This is not fussiness — it is about drainage and airflow.

When a pot sits flat on a patio, the drainage hole is effectively sealed against the slab. Water collects in the base of the compost with nowhere to go. If that water then freezes, it expands inside the pot, and if the pot is terracotta or glazed, it can crack from the inside out. Lifting the pot allows surplus water to drain freely and lets air circulate underneath.

• Pot feet are the neatest option. Clip-on feet, tripod feet or simple terracotta toadstools all work, and they raise the pot by 2–4cm, which is plenty.
• Bricks or stone offcuts do the job for heavier pots. Use three rather than two so the pot is genuinely stable in wind.
• A gravel bed is ideal for a group of large containers. A 5cm layer of coarse gravel or horticultural grit under the pots keeps them drained and looks deliberate rather than improvised.

While you are at it, clear any fallen leaves from around the base of the pot. Leaves trap damp against the sides and give slugs and vine weevils somewhere to shelter.

Insulate Terracotta and Glazed Pots

Terracotta is beautiful and hopeless in a hard frost. Even frost-resistant glazed pots can suffer, particularly if they are large and expensive enough to be worth protecting. Wrapping is simple and takes minutes.

Use bubble wrap — the small-bubble sort is easier to work with — and wrap it around the sides of the pot, not across the top. The roots and the compost are what matter; the foliage above is a separate job. Secure it with twine or a couple of bands of tape, and leave the drainage hole clear.

• Hessian is a smarter-looking alternative for pots near the front door. It insulates well and can be tied with jute twine.
• Bubble wrap plus a hessian outer layer gives the best of both — insulation and a bit of style.
• Group pots together in a sheltered corner against a wall. Clustering creates a microclimate and reduces wind exposure on all sides.
• Move small pots into a cold greenhouse, porch or shed. Even an unheated space takes the edge off the hardest frosts.

Do not wrap the crown of the plant in plastic. Trapped moisture around foliage in winter encourages mould. If you need to protect the top growth, use horticultural fleece instead, which breathes.

Ease Back on Watering

Overwatering kills more container plants in winter than cold does. Growth has slowed to almost nothing, so the plant is using a fraction of the water it needed in summer. Compost that stays wet for weeks will rot roots, and in a pot that means losing the plant entirely.

Aim to keep the compost barely moist — damp, never sodden. In a typical UK winter, containers in a sheltered spot may need no water at all for weeks at a time. It is worth a quick check every couple of weeks:

• Push a finger in 3–4cm. If it feels cold and wet, leave it well alone.
• Water only in the morning during a mild spell, so any excess has a chance to drain before the temperature drops overnight.
• Never let water sit in a saucer or tray. Empty them as a matter of routine.
• Keep watering evergreen shrubs and winter-flowering plants such as winter jasmine or hellebores — they are still active and can dry out under the shelter of a wall.

Pots under the overhang of a house are a special case. They may be bone dry in February despite everything around them being soaked, so check them by hand rather than assuming.

Protect the Compost Surface and Tender Plants

A little mulch on top of the compost does more than you might expect. A 2–3cm layer of bark chippings or grit slows heat loss from the surface and stops the freeze driving down so quickly. Grit is particularly good for alpines and anything that hates sitting wet around the neck.

For tender plants — olive, bay, citrus, phormium, agapanthus — consider the whole picture rather than one fix. Shelter from wind matters as much as temperature, because wind chill strips moisture from leaves that roots cannot replace from frozen compost. A temporary windbreak of fleece on canes, placed on the prevailing windward side, can be more useful than wrapping the pot itself.

Check ties and supports too. Stakes that have loosened in autumn gales may rub against bark all winter, and any plant that rocks in the wind will never fully settle.

A Few Checks Before Spring

Winter is not a season to ignore the garden entirely — a ten-minute walk round with a torch after a hard frost is time well spent. Look for cracked pots, roots pushing above the surface, compost that has frozen solid, and any wrapping that has come loose. If a pot has cracked, repot in early spring before growth restarts, and keep the broken pieces for crocks.

Come March, unwrap gradually. Pull the bubble wrap off on a mild, still day rather than during a cold snap, and leave fleece in place until the risk of hard frost has genuinely passed. Your pots will have come through the worst of it, and the plants inside them will be ready to grow away strongly.