Read the plot before you do anything else

By the time January arrives, most British allotments have taken weeks of rain and the ground is holding far more water than it can cope with. The temptation is to get out there and dig, but the most useful thing you can do in a wet winter is simply look. Walk the plot in wellies after a heavy downpour and note where the puddles gather. Water that drains away within a few hours is normal. Water that sits for days marks the low corners, the compacted patches, and the spots where a previous tenant buried rubble or trod a path that never quite recovered.

A rough drainage test is worth doing on any plot you are still getting to know. Dig a spade-sized hole about 30cm deep, fill it with water, and see how long it takes to disappear. If it drains within an hour or two, your soil is workable. If it is still full the next morning, you are dealing with heavy clay over compacted subsoil, and no amount of winter digging will fix that. Drainage, raised beds and organic matter will.

It also helps to find the lowest point of the site and check where the water wants to go. On many plots a single cleared channel along a boundary, or a shallow soakaway filled with gravel at the bottom corner, keeps the worst of the standing water away from the beds for the rest of the winter.

Keep off the beds and protect soil structure

Wet soil compresses like a sponge. Every bootprint on saturated ground squeezes the air out of the spaces between soil particles, and those air pockets are exactly what roots and worms need. Structure lost this way can take two or three seasons to repair, so the single best rule for a wet winter is to stay off the beds. Lay scaffold boards or old planks along the middle of each bed to spread your weight, and keep to permanent paths between them.

Digging is just as damaging. If the soil smears rather than crumbles when you push a fork into it, leave it alone. Forking wet clay creates a hard pan beneath the surface that roots struggle to break through all summer. Wait for a dry spell, or better still, don't dig at all and let the worms do the work under a thick mulch.

• Wear wellies with a good tread rather than boots that cake with mud and skid.
• Keep a plank by each bed so you never have an excuse to stand on the soil.
• Move anything heavy — water butts, compost bins, paving — before the ground softens, not after.
• If a bed is underwater, accept it. Plant it later rather than fighting the weather.

Raised beds and organic matter: the long game

Raised beds are the most reliable answer to a wet plot. Even lifting the soil by 15 to 20cm above the surrounding ground level gives roots a foot of free-draining growing space and lifts them clear of the water table. Timber, scaffold boards, bricks or woven panels all work; the important thing is that the sides hold the soil and that you can reach the middle from a path without treading on the bed itself.

Fill them with a mix of topsoil, well-rotted manure and garden compost, and top up every winter as the contents settle. Organic matter is the real fix for heavy ground. It opens up clay, improves drainage, feeds worm populations and holds moisture through the dry spells that always seem to follow a wet winter. Spread a 5cm layer of well-rotted manure or compost over the surface in late winter and let the worms pull it down rather than digging it in. For badly draining clay, fork in horticultural grit at roughly two buckets per square metre, plus leafmould if you have it. Build a leafmould bin in a corner now and you will have free soil conditioner within a year.

What to harvest and sow while it is wet

A wet winter plot is not an empty one. Leeks, parsnips, kale, Brussels sprouts, purple sprouting broccoli and winter salads will all stand through the cold. Leave parsnips in the ground until you need them — frost sweetens them — and lift leeks as required rather than all at once. If the ground is too wet to stand on, harvest from the path with a long-handled fork.

Late winter is also the moment for crops that need a cold start. Plant garlic and autumn-sown broad beans such as Aquadulce Claudia on ridges if your plot holds water, so the seeds sit above the waterlogged layer. Overwintering onion sets and shallots appreciate the same treatment. A cloche or a length of fleece over winter salad leaves keeps them picking for weeks longer, and protects young broad beans from the worst of the wind.

Use the quiet weeks for repairs and maintenance

Wet weather keeps you off the soil, so it is the perfect time to catch up on jobs that make everything easier in spring. Cleaning and sharpening tools now saves hours later, and a wiped-down, oiled spade or hoe will last years longer than one left muddy in a shed.

• Re-lay or top up paths with bark chip or gravel so you have somewhere dry to stand next season.
• Check raised bed timbers for rot and replace the worst boards before they collapse into the soil.
• Fix shed roofs, gutters and water butts — a full butt in March is worth its weight in summer.
• Clean, dry and oil hand tools, and sharpen secateurs and hoes on a wet afternoon.
• Service the lawnmower, clean seed trays and sort the shed so everything is findable in spring.

Plan next season's crops before spring arrives

Winter is when good plots are really made. Sit down with last year's notes, or start a notebook if you have none, and work out a rotation. Most allotment growers run a simple four-part cycle: brassicas, roots, potatoes, and legumes with onions and salads. Moving crops around prevents the build-up of pests and diseases and stops any one bed being exhausted.

Order seed while the catalogues are fresh, but be honest about how much you will actually grow and eat. Sketch a rough plan of each bed, note sowing dates for your area, and mark which crops struggled and why. Then, when the first dry week of March arrives, you will already know exactly where everything is going — and the drainage, the organic matter and the repaired paths will all be working quietly in your favour.