March is the month the growing year stops being a plan and starts being work. The light is stretching out, the soil is finally beginning to warm, and every seed packet on the rack suddenly looks like a good idea. It is also the month that punishes optimism. Two mild weeks can be followed by a sharp frost and a biting east wind just as the blossom opens. The way through is to sow in stages, keep fleece within reach, and hold some seed back for April.
Why March behaves the way it does
The most useful thing to understand about March is that air temperature and soil temperature are two different things. A sunny afternoon can push the thermometer to 14°C while the soil 10cm down is still sitting at 6°C — too cold for most seeds to do anything but sulk or rot. Hardy crops such as broad beans, parsnips and spinach will germinate once the soil holds around 7°C. Tender crops such as courgettes, sweetcorn and beans want closer to 12°C, which is why they wait until May.
Where you garden matters as much as the date. A sheltered plot in Cornwall can be three or four weeks ahead of an exposed site in Aberdeenshire, and a raised bed warms faster than heavy clay at the bottom of a garden. Treat any calendar, including this one, as a prompt rather than an instruction.
What to sow in March
Under cover
March belongs to the propagator and the sunny windowsill. Sow into moist seed compost, keep the tray somewhere warm and light, and move seedlings on as soon as they are big enough to handle.
- Tomatoes — late March suits most of the UK; sow earlier only if you have reliable heat and strong light.
- Chillies, peppers and aubergines — a March sowing still crops, just later than a February one.
- Brassicas — cabbage, calabrese, sprouts and kale for planting out in late spring.
- Leeks — sown thinly in a deep pot, they will be pencil-thick by June.
- Celery and celeriac — slow and fiddly, but worth it.
- Salad leaves and herbs — a tray of cut-and-come-again lettuce or basil keeps the kitchen supplied for weeks.
Straight into the soil
If the ground is workable — crumbly rather than claggy — these can be sown direct, ideally when a dry spell is forecast. Rake the surface fine, sow thinly, and label everything; March seedlings all look alike.
- Broad beans — hardy, and a good first crop for a new bed.
- Parsnips — fresh seed only, as old packets germinate poorly.
- Carrots, beetroot, radish and turnips — radish will be ready in a month.
- Spinach, chard and early salad — cover with fleece or a cloche for faster growth.
- Peas and mangetout — round-seeded varieties cope best with cold, wet soil.
- Onion sets and shallots — push them in so the tip just shows.
What to plant out, and what to protect
Onion sets, shallots and garlic that missed the autumn can all go in now. Early potatoes go into the ground from mid to late March in most areas, though a cold frame or a double layer of fleece will earn its keep if the forecast turns. Rhubarb crowns, strawberry plants, bare-root fruit bushes and hedging should be in before growth starts in earnest.
Anything raised indoors needs hardening off first: stand it outside in a sheltered spot for an hour on day one, then gradually longer over seven to ten days, bringing it in at night. Skip this and a fortnight of careful growing can be undone by one windy afternoon.
The rest of the year, month by month
Once March is behind you the sowing calendar opens up quickly. This is the shape of the year.
- April — maincrop potatoes, carrots, beetroot, lettuce, radish, spring onions and spinach go direct. Sweetcorn, courgettes and squash start under cover towards the end of the month.
- May — the busiest month. Beans, sweetcorn, squash and cucumbers go out once frost risk has passed; repeat sowings of salad, beetroot and carrots every fortnight.
- June — fill gaps with fast crops: lettuce, radish, French beans, spring onions. Sow winter brassicas for planting out next month.
- July — leeks and winter brassicas into their final positions; sow turnips, chard and kohlrabi for autumn.
- August — overwintering salads such as corn salad and land cress, spring cabbage, Japanese onions and spinach. Sow green manures on any empty ground.
- September — garlic and autumn onion sets; broad beans and hardy peas in mild areas; repair lawns while the soil is still warm.
- October — tulips and remaining spring bulbs, more garlic, bare-root fruit and hedging.
- November — last call for garlic and bare-root planting; mulch beds and cloche any winter salad.
- December and January — quiet months. Order seed, sharpen tools, prune dormant fruit. Onions, chillies and aubergines can be started under heat from late January.
- February — chit potatoes, sow broad beans, early peas and radish under cover, and start tomatoes at the very end of the month if your light is good.
Protecting what you sow
Cloches, fleece and cold frames are the difference between a March sowing and a March gamble. Fleece laid loosely over a row adds a couple of degrees and keeps pigeons and carrot fly off; a rigid cloche warms the soil underneath and suits salad, radish and early carrots. Lift covers on mild days to let air circulate, and water in the morning rather than the evening so foliage is dry by nightfall. Slugs are wide awake by now — a nightly torch patrol after rain is unglamorous and effective.
Your March checklist
If you do nothing else this month, work through this list and the season will look after itself.
- Test whether the soil is workable by squeezing a handful — if it clumps like plasticine, wait.
- Sow a small first batch rather than the whole packet, and note the date on the label.
- Keep fleece and cloches beside the beds, not in the shed.
- Harden off anything destined for outside, gradually and patiently.
- Sow successional salad every two to three weeks for a continuous supply.
- Check overwintered crops for slug damage, bolting and hungry pigeons.
March rewards the cautious gardener more than the eager one. Sow a little, protect it well, and you will have strong plants ready to surge away the moment the weather settles.
Photo: Hans / Pixabay
