Why pots feel the cold far more than borders

Frost in a border is a slow business. Soil is an enormous, damp mass, so it takes a hard and prolonged spell to freeze more than the top few centimetres. A container is the opposite: a small body of compost wrapped in cold air on every side, including underneath, where it sits in contact with a slab that has been chilled all night. Roots in a pot can freeze solid while roots thirty centimetres away in open ground are perfectly comfortable.

Wind makes it worse. A cold easterly will strip moisture from evergreen leaves at a surprising rate, and frozen compost means the roots cannot take up water to replace it. In Britain, that pairing of frozen roots and drying wind kills far more container evergreens than temperature alone. Add a terracotta pot that expands and cracks, or a compost surface that heaves and pushes a plant proud of the soil, and you can see why containers need a bit of management from November onwards.

Hardy evergreens that earn their keep

The backbone of a good winter pot is foliage that stays smart without fuss. Look for compact, slow-growing plants with small or leathery leaves, which lose less moisture than big soft ones.

• Skimmia japonica — neat domes of glossy foliage with tight red buds through the winter, opening in spring. Happy in shade, happier still in a loam-based compost.
• Ilex crenata — Japanese holly, with tiny leaves that clip beautifully. A tough, hardier alternative to box in cold gardens.
• Euonymus fortunei — 'Emerald Gaiety' and 'Emerald 'n' Gold' shrug off wind and shade, and trail nicely over a pot rim.
• Viburnum tinus — evergreen, tolerant of a large pot, and carries pink-white flowers from late winter into spring.
• Dwarf conifers such as Thuja occidentalis 'Danica' or a slow pine — give structure and a solid silhouette, and ask almost nothing.
• Small rhododendrons and Japanese azaleas — evergreen, tidy, but they need ericaceous compost and shelter from the worst of the wind.
• Whipcord or small-leaved hebes — good in a well-drained pot and against a wall, where drainage is sharp.
• Aucuba japonica — for the gloomy corner where nothing else wants to live.

Winter-flowering heathers: small plants, big effect

Heathers are the quiet heroes of the frosty patio. The winter-flowering sorts — Erica carnea and the Erica x darleyensis hybrids — bloom from November onwards, often right through the worst weather, in white, pink, rose and deep crimson. They knit into a low mat that suppresses weeds and covers the compost surface, which is exactly what you want in a pot.

Plant them in ericaceous compost, two or three to a wide container, and keep them near the front where you can see them. A handful of varieties flowering at slightly different times will carry a pot from autumn into April. Trim lightly after flowering — just below the spent flower spikes, never into the old bare wood, because heathers rarely regrow from it. Calluna varieties then take over for summer and autumn colour in the same pot.

Get every pot up onto feet

If you do one thing this week, do this. Pot feet lift a container two or three centimetres clear of the paving, and the difference is remarkable. Water drains freely instead of pooling beneath and freezing into a solid block. Air moves underneath, so the base of the pot is not in constant contact with a cold slab. The drainage hole stays open. And the pot will not bond itself to the patio, which means you can still move it in January.

Three feet under a round pot is plenty; two battens of timber will do for a heavy stone trough. If you cannot lift a pot, tip it very slightly onto a piece of slate so it never stands in a puddle. Group containers together in a sheltered corner against a house wall, and wrap the outside of the pot — not the foliage — in bubble wrap or hessian. A couple of centimetres of bark mulch or gravel on top of the compost insulates the roots and stops the surface heaving.

Compost, water and cold wind

Loam-based composts, such as a John Innes No 2 or 3, cope far better with repeated freezing and thawing than light multipurpose mixes, because their structure holds together. Bigger pots are also easier to look after: a larger volume of compost takes much longer to freeze through, so err on the generous side when choosing containers.

Watering in winter sounds odd, but evergreens keep losing moisture all season. On a mild morning, check the compost with your finger. If it is dry, water gently, and do it early enough that surplus drains away before evening. Never water compost that is frozen, and never feed — plants are not growing and food will simply sit there. Take saucers away for the winter, since standing water becomes ice, which can crack a pot and rot roots.

Small jobs on a frosty morning

• Knock heavy snow off evergreens with a soft broom, brushing upwards, so branches do not splay.
• Leave frosted foliage alone. Blackened leaves shelter the growth beneath — wait until late spring before you cut anything back.
• Keep de-icing salt away from containers; move pots back from paths that get gritted.
• Check for frost heave after a hard night and firm any plant that has been pushed up, topping up compost if needed.
• Shuffle the smallest pots into a porch, cold greenhouse or against a sheltered wall for the worst fortnight.
• Note which pots look bare in January, so you can plant a winter heather or a skimmia into the gap in autumn.

Do these few things and your patio will still have shape, colour and something in flower when everything else has given up.