THE FIRST FROSTS: WHAT TO DO IN THE GARDEN BEFORE THE FIRST NIGHT BELOW ZERO

Frost does not burn the leaf. What it does is freeze the water inside the cells, and as it freezes it takes up more room and bursts them. The plant does not register it until the thaw: then the broken tissue darkens and goes soft.

Which is why the damage always shows up two days late, when there is nothing left to do about it. So the work is now.

Not all frosts are the same

White frost. The hoar frost kind, with damp air. It is the gentlest: the water freezes on the surface of the leaf, and the layer of ice even protects it a little.

Black frost. Dry air, no hoar frost, and far more damaging. The ice forms inside the tissue directly. It takes its name from the colour the foliage turns the next day.

Radiation frost. A clear, windless night, with the ground heat escaping upwards. It is the classic autumn frost and the one you can actually fight: anything that covers from above returns that heat. If the night is cloudy or windy, there is no radiation frost.

The practical rule: a clear, still, dry night in November is a frost night. If the evening looks like that, go out into the garden.

The four jobs for the evening before

Water the morning before. It sounds contradictory and it is not: damp soil holds far more heat than dry soil and gives it back overnight. It can be worth a degree or two. In the morning, never at dusk, because cold water on the surface at nightfall does the opposite.

Bring in anything in a pot. Pots go first, because the root ball freezes from all four sides. If they will not fit indoors, group them all in a sheltered corner, touching each other and against a wall: that way they shelter one another.

With citrus in pots there is one point hardly anyone allows for: bringing them into the living room does them more harm than leaving them outside.

Mulch the base. Ten centimetres of dry leaves, straw, bark or compost around the trunk. It will not save the foliage, but it saves the roots, and with live roots the plant comes back in spring even if it is stripped bare.

Cover what is tender. Horticultural fleece, hessian, cardboard or an old sheet. Two rules nearly everyone skips: it must not touch the foliage, because wherever it touches, that spot freezes, so use three canes to hold it off; and it must reach the ground, because the heat comes from the soil and a cover left open at the bottom does nothing at all.

And take it off in the morning. In sunshine, the temperature under plastic gets absurd.

What not to do right now

Do not feed. Not even "just a little to help it cope". Nitrogen pushes out soft new growth, and soft growth is the first thing to freeze. No feeding until February.

Do not prune. Every cut is an open wound, and pruning stimulates growth as well. Fruit trees are pruned in deep winter, with the tree fully dormant.

Do not cut off what has already been frosted. This is the hardest one to resist. The burnt part, however ugly, is acting as a coat for what is underneath. Cut it in spring, once you can see where it is shooting from.

Do not water at midday. And especially not the foliage. Water on the leaves plus a cold night is guaranteed damage.

What is worth doing these days

Rake the fallen leaves off the lawn and leave them in the beds. On grass they smother it; in a bed they are the best mulch there is, and free.

Drain the hoses and outside taps. Water inside the pipe freezes, expands and splits it. It is the breakage that happens every winter.

Lift the pots off the ground. Blocks, battens or a couple of tiles. Cold ground freezes a pot from below.

And plant. The arrival of frost does not close the season: November is a good month for spring bulbs, bare-root trees and shrubs, hedging and fruit trees. The plant spends the winter making roots without having to support any foliage, and in spring it starts away with an advantage one planted in March never gets.

If it has already frosted and taken something

Wait. A plant can be black on top and perfectly alive inside. Scratch a little bark with a fingernail: if it is green underneath, the stem is alive.

Water sparingly once it thaws. Frozen roots do not drink, and waterlogging damaged roots finishes them off.

Do not move it or give it an emergency feed. The only thing it needs is time.

And make a note of which corner of the garden froze first. That information, winter after winter, is what eventually teaches you where you can plant what, and where you cannot.