Spring Seed Sowing Calendar for Beginners

Spring in the UK rarely arrives in a tidy, predictable fashion. One week you are sowing in shirtsleeves, the next a cold east wind has you reaching for the fleece. That is exactly why a simple sowing calendar helps. It gives you a framework to work from, then you can nudge it earlier or later depending on where you garden — Cornwall is a fortnight ahead of Cumbria on most things, and a sheltered south-facing wall is worth two weeks of extra season all by itself.

The single most useful number to remember is soil temperature. Most hardy vegetables and annuals will germinate once the soil sits at around 7°C, while tender crops such as courgettes, beans and basil want 12°C or more. Air temperature on a bright March afternoon tells you very little; the ground tells you the truth.

February: Start Slow, Start Small

This is the month for sowing anything that needs a long run-up before summer. If you have a windowsill, a heated propagator or a bright porch, use it now.

• Onions and leeks: sow under cover in modules at about 15°C. Leeks are slow to bulk up, so an early start pays off by August.
• Chillies and aubergines: they need 18–21°C to germinate and a long season. Sow now, keep them warm, and move them to the brightest spot you have once they are up.
• Sweet peas: sow in deep pots or root trainers. A cool, bright windowsill suits them far better than a hot kitchen.
• Hardy annuals: calendula, cornflower and nigella can all be started in modules. A light windowsill is plenty — no bottom heat needed.

Broad beans are the exception that can go straight into the ground, provided the soil is workable and not waterlogged. A cloche over the row will speed germination noticeably.

March: The Engine Room of the Year

March is when the sowing list suddenly gets long. Light levels are climbing fast, which matters more than warmth for sturdy growth. Weak, leggy seedlings are almost always a light problem, not a heat problem.

• Tomatoes: sow under cover at 18–20°C. Once germinated, drop the temperature slightly and give them maximum light to keep them stocky.
• Brassicas: cabbage, broccoli and kale can be sown in modules. Prick them out into individual pots before they root through the tray.
• Salad leaves: lettuce, rocket and mizuna sown in modules or a cold frame will give you cut-and-come-again leaves from late April.
• Herbs: basil needs warmth and light; parsley, chives and coriander are happy at around 15°C.

If you garden on heavy clay, keep off wet beds this month. Sowing into cold, claggy soil is one of the surest ways to lose a crop.

April: Hardy Crops Go Out, Tender Crops Stay In

By April the soil is usually warming properly, and direct sowing becomes worthwhile. Wait until the ground has dried enough to crumble in your hand — if it balls up like plasticine, give it another week.

• Roots: carrots, beetroot, parsnips and radishes all resent transplanting, so sow them where they are to grow. Radishes are ready in as little as four weeks and make a useful row marker between slower crops.
• Leaf and stem: spinach, chard and perpetual spinach can go in now, and will crop right through to autumn if kept watered.
• Peas: direct sow in a flat-bottomed drill about 5cm deep, spaced roughly 7cm apart.

Begin hardening off anything raised indoors. Move plants to a cold frame or a sheltered spot for a few hours a day, building up over a fortnight. It is tedious, but it prevents the check that sets seedlings back for weeks.

May: Tender Crops and Successional Sowing

Wait for the last frost before planting out tender crops. In southern England that is usually mid-May; in northern England and Scotland, late May or early June is safer. A sheet of fleece over an early planting buys you a fortnight of insurance.

• Courgettes, squashes and cucumbers: plant out once nights are reliably above 8°C. Give courgettes a metre of space each — they will use it.
• Beans: runner and French beans go in after the frost risk passes. Sow a second row three weeks later for a longer harvest.
• Sweetcorn: plant in blocks rather than rows for better pollination.

Keep sowing salad, radish and coriander every two to three weeks. A small sowing fortnightly will feed you far better than one enormous row that bolts all at once.

Spacing, Thinning and a Little Patience

Spacing is where beginners lose most of their harvest. Overcrowded seedlings compete for light, water and nutrients, and the result is weak plants and disappointing yields. Thin carrots to about 5cm apart, beetroot to 10cm and lettuce to 20cm. Yes, it feels wasteful pulling out healthy seedlings — but the ones that remain will reward you.

Water seeds with a gentle rose rather than a jet, keep labels legible, and check pots daily once the weather warms. Above all, do not panic if March throws snow at you. Seeds are patient, and the season is long. Sow a little, sow often, and let the garden tell you what it wants.