When to sow aubergines

Aubergines need a long, warm season: roughly five months from sowing to the first fruit. So start early. Sow indoors from February to mid-March. With a heated propagator and a grow light you can begin in January, but on a windowsill the extra weeks mostly give you leggy seedlings.

Plan on about eight weeks from sowing until the young plants are ready to go out. They go into an unheated greenhouse from early May, and outdoors only once frost is over: in Germany, Austria and Switzerland that means after the Eisheiligen in mid-May, in the UK late May or early June.

Aubergines are even more sensitive to cold than tomatoes. Wait until the nights stay above 50°F, ideally nearer 59°F. A cold snap after planting doesn't kill them outright, but it stops their growth for weeks.

Sow into seed compost, 0.2–0.4 in deep, and keep the pots warm: 72–82°F is ideal, and below about 68°F germination slows to a crawl. A heated propagator makes all the difference. Seedlings appear after one to three weeks.

Once the first true leaf shows, prick the seedlings out into pots 2.8–4 in across. From then on they grow happily at 61–70°F, as brightly as you can give them. Pot them on again if the roots fill the pot before planting time.

Before they go outside, harden the plants off gradually over several days. Choose the sunniest, most sheltered spot you have and rich, humus-rich soil, and work in compost before planting.

Space plants 20–24 in apart with 24–31 in between rows. A 120 × 80 cm raised bed holds four plants, set in two staggered rows. In a pot, give each plant at least 12 in across; a dark mulch or mulch fleece on the soil warms the roots.

Aubergines want warmth above all: days of 77–86°F suit them best. Under glass that comes easily; outdoors it's why a sheltered spot, a south wall or black mulch makes such a difference.

When a plant reaches about 12 in, pinch out the growing tip so it branches and stays bushy. Plants grow up to about 39 in tall and their stems break easily under the fruit, so give each one a stake from the start.

Big-fruited varieties can only ripen a handful of fruit in our summers. Once five or six have set, remove any further flowers so the plant puts its energy into those.

Keep the soil evenly moist and never let pots dry out. From the first flowers, give a liquid feed rich in potassium, such as tomato feed or comfrey tea, every two to three weeks. German gardening advice ranks aubergines as medium to heavy feeders (Mittel- bis Starkzehrer).

Under glass the first fruit can be ready in late July; most aubergines are picked in August and September, about twelve weeks after planting out. The season ends with the first cold nights.

Pick when a fruit has reached its full size and colour and the skin is glossy. Once the shine turns dull, it's over-ripe: the seeds turn brown and hard and the flesh can taste bitter.

Cut the fruit with a knife or secateurs, leaving 0.8–1.2 in of stalk, rather than twisting it off. Aubergines don't keep long. Store them somewhere cool, around 50°F, and use them within about a week; in the fridge they only last a few days.

Beyond the classic long, near-black fruit there are round, white, striped and golf-ball-sized aubergines. The RHS gives its Award of Garden Merit to 'Bonica', 'Clara', 'Galine' and 'Kaberi'; the Bavarian garden academy names 'Madonna F1', the white 'Mohican', the small 'Bambino' and 'Black Beauty' as examples.

For growing outdoors or in a short summer, pick early, compact or small-fruited varieties. They set more fruit that actually ripens before autumn than the big-fruited types.

Under glass, red spider mite and whitefly are the usual trouble, along with aphids on young shoots. Check the undersides of the leaves regularly. Outdoors in Central Europe, Colorado potato beetles and their larvae happily eat aubergine leaves too; pick them off by hand.

Verticillium wilt is the disease to know. The fungus lives in the soil and enters through the roots: lower leaves yellow, often on one side of the plant first, and the plant wilts in hot weather. There is no cure. Pull out affected plants and don't grow aubergines, tomatoes or potatoes in that spot again for years.

Aubergines belong to the nightshade family with tomatoes, peppers and potatoes. The RHS says aubergines and peppers can go anywhere in a rotation, but because verticillium attacks the whole group and lasts for years in soil, a three- to four-year break before any nightshade returns is the safer rule.

Planting tables suggest lettuce, spinach or cabbages next to aubergines and warn against tomatoes and peppers. We found no study behind these pairings; they are tradition. Low, quick crops like lettuce at least don't compete much.

Two points with a real reason: aubergines start slowly, so keep sprawling courgettes and squash from smothering them, and treat tomatoes, peppers and potatoes as the same crop when you plan your rotation.