Why a Sudden Cold Snap Catches Us Out

Mild autumn weather lulls us all into a false sense of security. Days drift along at ten or twelve degrees, the grass keeps growing, and the thought of a hard frost feels a long way off. Then a clear, still night arrives, the temperature drops faster than forecast, and by morning the tender plants you left out are slumped and blackened. A single night at minus four or five can undo a whole season's work, particularly in a garden that has been basking in unseasonal warmth.

The good news is that most frost damage is entirely avoidable. You do not need a heated greenhouse or expensive kit. You need an hour or two of preparation, ideally before the first proper cold spell rather than the morning after it. Work through the jobs below and your garden will come through a cold snap with far less scarring.

Move Tender Pots and Containers Under Cover

Plants in containers are the most vulnerable of all, because their roots sit above ground with nothing but a thin wall of terracotta or plastic between them and the freezing air. The compost in a small pot can freeze solid within a few hours, and once the roots are frozen the plant is usually finished.

Before temperatures dip below freezing overnight, move anything tender to a sheltered spot:

• Shift pots of citrus, olives, bay, lavender and other borderline plants against a south or west-facing house wall, where residual warmth from the bricks makes a real difference.
• Raise pots onto terracotta feet, bricks or wooden blocks so they are not sitting directly on freezing paving. Air can then circulate underneath.
• Group containers tightly together. Clustering them creates a microclimate and reduces the surface area exposed to the cold.
• Wrap the outside of larger pots with bubble wrap or hessian, secured with twine, but leave the drainage holes clear so water can still escape.
• Take small, precious pots into an unheated porch, garage or shed. Cool but frost-free is ideal.

If a pot is too heavy to shift, at least wrap it and cover the top growth with a double layer of horticultural fleece. Remove the fleece during the day so the plant gets light and air.

Mulch Exposed Roots and Bare Soil

Bare soil loses heat quickly, and repeated freezing and thawing heaves young plants clean out of the ground. A generous mulch acts like a duvet, trapping warmth in the soil and keeping the temperature around the roots far more stable.

Spread a layer five to seven centimetres deep around:

• Newly planted shrubs, roses and fruit bushes, especially anything put in this autumn.
• Herbaceous perennials that have died back, leaving crowns sitting close to the surface.
• Raspberry canes, strawberry plants and other soft fruit.
• Tender perennials such as penstemons, agapanthus and hardy fuchsias.

Bark chippings, leaf mould, well-rotted compost or garden compost all work well. Keep the mulch a few centimetres clear of stems and trunks to avoid rotting the bark, and never pile it over the crown of a plant. For tree ferns and bananas, bundle the fronds upwards and stuff the crown with dry straw or fleece, then tie it securely.

Insulate Outdoor Taps and Pipes

Frozen pipes are one of the most expensive and irritating consequences of a cold snap, and the outdoor tap is nearly always the first casualty. Water left sitting in the pipe expands as it freezes, and the resulting split often only becomes obvious when the thaw arrives and water starts running down the wall.

A few simple measures will prevent it:

• Find the indoor isolator valve for your outside tap and turn it off before the cold arrives.
• Open the outdoor tap afterwards to drain any remaining water from the pipe.
• Fit a foam tap jacket, or wrap the tap in an old towel, bubble wrap and a plastic bag tied securely underneath.
• Lag any exposed pipework running along a wall or through a cold outbuilding.
• Disconnect hosepipes and store them in a shed or garage, and drain any hose reel.

If you have an irrigation system or a water butt, drain what you can and check that taps and connectors are empty. A little effort now saves a plumber's bill later.

Protect Veg, Evergreens and the Lawn

Winter vegetables are tougher than they look, but a hard, long frost will still catch out leeks, winter salads and anything under cover. Throw fleece or a cloche over salad leaves, parsley and coriander. Brassicas generally shrug off the cold, but a net weighted down will stop pigeons stripping them when other food runs short.

Evergreens suffer in a different way. Frozen ground means roots cannot replace water lost through the leaves, so plants can scorch and brown. Water evergreens thoroughly during any mild spell before a cold snap, and shelter prized specimens from cold winds with a windbreak of fleece or hessian.

As for the lawn, keep off it while it is frosted. Walking on frozen grass bruises the blades, and the damage shows as brown footprints for weeks. Leave mowing until growth genuinely restarts in spring.

What to Do When the Thaw Arrives

Resist the urge to tidy up the moment the snow clears. Frosted growth often looks far worse than it is, and cutting back too early exposes fresh wounds to the next cold night. Wait until the risk of hard frost has passed, then trim away anything genuinely mushy and black.

Check pots and containers for cracking, firm any plants that have been lifted by the frost, and replace mulch that has blown away. Finally, keep a full bird bath or shallow dish of unfrozen water available — wildlife struggles badly in a cold snap, and a steady supply of fresh water is one of the kindest things you can offer. A garden prepared properly in advance will reward you with a much gentler spring.