Read the forecast — and your own garden

Every winter, the same thing happens. The forecast promises a sharp overnight frost, and half the nation's pelargoniums are still sitting out on the patio in their terracotta pots. A little preparation in late autumn saves a great deal of regret in January, and most of the work takes an afternoon rather than a weekend.

Before you do anything, work out where the cold actually settles. Frost behaves like water: it flows downhill and pools in hollows. The bottom of a sloping garden, the strip beside a north-facing fence and the ground beneath a dense hedge will always be two or three degrees colder than a sheltered south-facing wall. Those low spots are where you should plant the hardy stuff, and where tender plants should never overwinter.

Soil matters too. Heavy clay holds water for weeks, and cold, sodden roots rot far more readily than dry ones. If your beds sit wet through winter, drainage is your priority long before insulation. Sandy, free-draining ground is far more forgiving, though it dries out and heaves in a hard freeze.

Tender plants in pots: move, group, insulate

Anything growing in a container is far more exposed than the same plant in open ground. Compost in a pot freezes solid from all sides, and the roots have nowhere to retreat to. Terracotta is especially vulnerable — trapped water expands, and the pot cracks.

• Move what you can. Bring citrus, olive trees, fuchsias, pelargoniums and agapanthus into a greenhouse, porch or cool conservatory. A frost-free shed will do for many, provided it is light enough.
• Group what stays. Cluster pots together against a house wall, ideally a south or west-facing one, and pack the gaps with straw or scrunched newspaper. Massed pots insulate one another.
• Get them off the ground. Stand pots on pot feet, bricks or timber battens so water drains freely and the base is not in contact with frozen paving.
• Wrap the vulnerable. Bubble wrap around the pot, tied at the rim, protects the rootball. Hessian or horticultural fleece over the top of tender evergreens keeps the worst of the wind off the leaves.
• Ditch the saucers. A saucer full of frozen water is a slow death sentence for a containerised plant.

Timing is everything with tender tubers. Dahlias, cannas and gladioli should be lifted after the first frost has blackened their foliage, then dried and stored in barely damp compost in a frost-free place.

Mulch the roots, but keep the collar clear

A generous mulch is the single best protection for plants in the ground. Spread a layer five to seven centimetres deep over the root zone using bark chippings, well-rotted compost, leafmould or garden compost. This insulates the soil, moderates the freeze-thaw cycle that heaves plants out of the ground, and feeds the worms doing the work below.

One caution: keep the mulch clear of stems and crowns. Piling it against the base of a shrub or the crown of a herbaceous perennial traps moisture and encourages rot. Think of it as a blanket around the shoulders rather than a scarf pulled over the face. Tender crowns such as heuchera and agapanthus are particularly prone to this.

For extra insurance, a loose mound of dry leaves or straw over the crown of borderline-hardy perennials works well, and can be pulled back in March.

Drainage matters more than cold

In a British winter, more plants are killed by wet feet than by low temperatures. Waterlogging starves roots of oxygen, and the damage often only shows up in spring as a plant that fails to leaf.

• Fork over compacted beds before the ground closes up, taking care not to damage shallow roots.
• Improve heavy clay by working in grit or bulky organic matter on the surface and letting the worms pull it down.
• Clear gutters, downpipes and drains so that autumn leaf fall does not send water cascading onto borders.
• Check water butts and soakaways are empty enough to take the winter rain.
• Raise the level of boggy beds with a top dressing of grit and compost, or consider a raised bed for plants that insist on sharp drainage.

If a border floods every year, stop fighting it and plant accordingly. Dogwood, willow, astilbe and many ferns will shrug off a wet winter that would see off lavender and rosemary.

Snow: help where it is heavy, leave where it is light

A light dusting of snow is a gift. It insulates the ground beneath and protects low-growing plants from the wind. Leave it where it falls.

Heavy, wet snow is a different matter. It is remarkably weighty, and it will snap the branches of conifers, clipped box and evergreen hedges. Knock it off gently with a soft broom, working upwards from underneath so you lift the branch rather than pressing it down. Never try to shift snow that has frozen solid onto foliage — you will do more damage than the weather would have. Wait for a thaw.

Avoid walking on a frozen lawn, as the grass blades shatter and leave brown footprints well into spring. Keep salt and grit for paths and drives only, well away from beds; use sand or coarse grit near planting instead.

A few last jobs before the first hard frost

• Insulate the greenhouse with bubble wrap and ventilate briefly on mild, bright days.
• Lag outdoor taps and drain hosepipes before they split.
• Top up bird feeders and keep a shallow dish of unfrozen water available.
• Float a ball in the pond to keep a hole open in the ice rather than breaking it, which sends shockwaves through the water.
• Check stored produce in sheds and garages for damp and mice.

Do these jobs on a bright, dry afternoon in late autumn and you can spend the coldest weeks of the year indoors, watching the garden rather than worrying about it.