When to sow carrots

Carrots are sown where they are to grow, never raised in pots: the taproot hates being moved. In Germany, Austria and Switzerland the first sowings of early varieties go in from March, once the soil has dried out enough to rake fine. In the UK the main outdoor season runs from April to early July, with February and March sowings possible under cloches or fleece.

Sow small batches every three to four weeks until June for a steady supply of young roots. Maincrop and storage carrots go in from May to June, and you can sow a fast early variety as late as early July for tender autumn carrots.

Carrot seed starts to germinate at about 41°F, but in cold soil it can sit for a month. It comes up much faster once the soil warms, so there is little to gain from sowing into cold, wet ground.

Carrots want sun, an open spot and deep, loose soil without stones. Stones, clods and compacted layers make the roots fork, and so does fresh manure. Work the bed finely and deeply; on heavy clay, a raised bed or a ridge of soil gives much better roots. Compost from the previous crop is enough feed: carrots are light to medium feeders.

Draw shallow drills 0.4–0.8 in deep, a little shallower in heavy soil, and 8–10 in apart. Sow thinly, cover, and press the soil down lightly so the seed has good contact. Keep the drill evenly moist until the seedlings are up; a crust on dry soil is hard for them to break through.

Because carrots are so slow, many gardeners mix in a few radish seeds. The radishes come up within a week and mark the row, so you can hoe between rows early, and they are pulled long before the carrots need the space.

Once the seedlings have a few true leaves, thin them to 1.2–2 in apart; leave up to 2.8 in for large maincrop roots. Thin on a still evening, take the thinnings away and firm the soil again, because the smell attracts carrot fly. Sowing thinly, or using seed tape, saves most of this work.

In a 120 × 80 cm raised bed you get four rows 8 in apart. At 1.6 in in the row that is about 30 carrots per row, some 120 in all; thinned to 2 in, about 96.

Keep the rows weed-free, especially in the first weeks when the slow seedlings are easily smothered. Hoe shallowly or weed by hand.

Established carrots need little watering. In a dry spell, give a thorough soak about every two weeks rather than a little often. What matters most is evenness: a heavy watering after a long dry spell makes the roots split, and too much water gives lush leaves and less sweetness.

If the tops of the roots push out of the soil, draw a little earth over them. Exposed shoulders turn green and taste bitter there.

Early varieties are ready about 10–12 weeks after sowing; maincrop carrots take four to five months or more. Pull them as soon as they are big enough to use: young carrots are the sweetest. Loosen the soil with a fork first if it is firm, and twist the leaves off rather than cutting close to the root.

Late carrots can stay in the ground into winter under a thick layer of straw, and you dig them as needed. On wet, heavy soil, or where slugs and carrot fly larvae are a problem, lift them in autumn instead.

For storing, use only sound, undamaged roots. They keep best just above freezing, around 32–34°F, and very humid, in boxes of damp sand or a clamp. Keep them away from apples and pears: the ethylene those give off makes carrots bitter.

Early varieties, often short Nantes or round Paris types, grow fast and are best eaten fresh; sow them from March. Maincrop and storage varieties grow longer and bigger, need a longer season and are sown in May and June for lifting in autumn.

Coloured carrots in yellow, purple or red are grown the same way. If carrot fly is a regular problem, varieties such as 'Flyaway' or 'Resistafly' are less attractive to it, though not immune.

Carrot fly is the main pest. Its creamy maggots tunnel into the roots and leave rusty-brown scars. The first generation lays eggs from late May into June, the second in August and September, and the second often does the most damage to carrots left for winter.

The surest protection is fine insect mesh laid over the bed from sowing to harvest, tucked in all round so the low-flying females can't get underneath. Low fences around the bed are commonly recommended, but a full cover works better. An open, breezy site helps too.

You can also dodge the fly with timing: early carrots pulled by mid-June miss most of the first generation, and sowings made after mid-May avoid it. Sow thinly so there is little to thin, and never leave thinnings lying on the bed.

Forked roots come from stones, compacted soil or fresh manure. Split roots come from uneven watering. Green, bitter shoulders come from light on exposed tops.

Carrots belong to the carrot family (Apiaceae), with parsnip, parsley, celery and celeriac, dill and fennel. They share pests and soil-borne diseases, so leave at least four years before any of them grows in the same bed again.

The classic pairing is carrots with onions or leeks, said to confuse carrot fly by masking the smell. There is some research with onions, but the effect needed a lot of onions, and the RHS treats the idea with caution. Treat it as tradition that does no harm, not as protection: mesh is what reliably works.

Lettuce, radish, peas and kohlrabi are often listed as good neighbours too. There is little evidence either way; they simply share the bed well. The rule with a real reason is to keep carrots apart, in space and time, from other carrot-family crops.