Why Raised Beds Need a Spring MOT

Raised beds earn their keep in small gardens. They drain faster than open ground, warm up sooner in spring, and save your back from endless bending. But a winter of rain, frost and wind takes its toll. Levels drop as the compost settles, nutrients leach away with every downpour, and weeds quietly get a foothold in the bare soil.

Spending a couple of hours on preparation now pays you back all season. You will be sowing into a bed that holds moisture properly, feeds your plants steadily and gives seedlings the strong start they need. The best part is that you can do all of this in small bursts — an hour here, half an hour there — long before the main sowing rush begins.

Clear the Ground and Inspect the Structure

Start by pulling out anything that has overwintered. Annual weeds come up easily after rain, roots and all, especially if you use a hand fork to loosen the soil first. Perennials such as couch grass, bindweed and dandelions need more patience: trace each root and remove as much as you can, because even a small fragment will regrow.

Then give the bed itself a once-over:

• Check the boards or sleepers for rot, loose screws and splintered edges, and replace anything that has gone soft.
• Push the corners back into square and firm any posts that have shifted with the frost.
• Look along the top edge — if it sits lower than 20cm above the soil, you will struggle to keep a decent depth of compost in place.
• Remove old plant debris, spent mulch and any netting or supports that have seen better days.

If the soil inside the bed is waterlogged and claggy, stay off it. Working wet soil destroys its structure and leaves you with hard clods that take months to break down.

Top Up with Compost and Organic Matter

Most raised beds sink by 5–10cm over a year, so expect to add a decent layer of organic matter each spring. As a rule of thumb, spread 5–8cm of well-rotted compost or soil conditioner across the surface and let the worms work it in. There is no need to dig it over — a gentle fork-over of the top few centimetres is plenty.

If your beds are very low, top them up with a mix of roughly two parts compost to one part loam-based topsoil. Straight compost alone dries out too quickly in summer and shrinks as it decomposes. For hungry crops such as courgettes, brassicas and tomatoes, add a handful of slow-release organic fertiliser per square metre at the same time.

This is also the moment to correct the soil. If you grow a lot of brassicas, a dusting of lime keeps clubroot at bay and raises the pH. If you are planting blueberries or potatoes, leave it alone — they prefer things on the acidic side.

Check Drainage Before You Sow

Good drainage is the difference between happy roots and a bed full of rot. Water should disappear from the surface within an hour of heavy rain. If it pools, the problem is usually compaction or a blocked base.

• Fork over the lower layer gently to open up channels without turning the soil upside down.
• If the bed sits on a hard surface, check that the drainage holes or gaps underneath are clear of roots, gravel and old compost.
• For beds on soil, dig a narrow channel along one side if water regularly collects.
• Work in grit or coarse bark to heavy clay, roughly a bucketful per square metre.

Once water drains freely, cover the surface to stop the spring rain washing away all your hard work.

Warm the Soil for an Earlier Start

Soil temperature matters more than air temperature in early spring. Most seeds need a steady 7°C to germinate, and tender crops such as beans and sweetcorn want closer to 12°C. A raised bed warms faster than the ground, and you can push it further with a little help.

Clear polythene, fleece or a cloche laid over the surface two or three weeks before sowing can raise soil temperature by several degrees. Black polythene works best for quick results — leave it in place, weighted at the edges, and the top 10cm will be noticeably warmer and drier. Cloches do the same job for individual rows, and they also keep late frost off young leaves.

If you plan to plant out in April, start warming the beds in late February or early March. A fortnight of cover is usually enough to bring sowing forward by two to three weeks.

Final Touches and Your First Sowings

Before you open the seed packets, take stock of what each bed will grow. Rotating crops between beds keeps pests and diseases guessing, so move your legumes, roots, brassicas and potatoes on by one position each year. Mark out rows with string or a straight edge, and keep paths wide enough to kneel on comfortably — 30cm is a sensible minimum in a small plot.

Then start with the tough ones. Broad beans, peas, onion sets, spinach and early salads will all cope with cool soil under fleece. Hold back the courgettes, French beans and tomatoes until May. Water gently after sowing, keep the surface moist but never sodden, and label everything — you will forget which variety is which by June.

Do these jobs well and your raised beds will reward you with healthier seedlings, fewer weeds and a longer, more generous growing season.