When to sow French beans

French beans come from warm climates and hate cold, wet soil: the seed rots or germinates so slowly that pests get to it first. Wait until the soil is at least 50°F, better 59°F. In Germany, Austria and Switzerland that usually means mid-May, after the 'Ice Saints' cold spell around 11–15 May. In the UK, sow outdoors from late May in the south and early June further north.

Dwarf beans crop over just two or three weeks, so sow a short row every two to three weeks until early July. The last sowings still have time to crop before autumn.

For an earlier start, sow in pots indoors from late April and plant out once frost is over, or cover early outdoor sowings with fleece.

This guide covers dwarf (bush) French beans. Climbing French beans are grown like runner beans; see the runner bean guide.

Pick a warm, sunny, sheltered spot with free-draining, humus-rich soil. Very sandy or heavy clay soils are hard going. Work in compost the autumn before rather than just before sowing: fresh organic matter attracts bean seed fly.

Sow 1.2–1.6 in deep, a bean every 3–4 in in rows 16–20 in apart. Many German gardeners sow in clumps instead: four to six beans together, with 16 in between clumps. Both work; clumps support each other a little in wind.

In a 120 × 80 cm raised bed, two rows along the long side take 24–30 beans. That is plenty for one sowing; sow the rest of the bed two or three weeks later.

Keep the rows weeded for the first four to six weeks, until the plants close over. Until they flower, beans need little water. Once they flower and set pods, water in dry spells, and a mulch keeps the soil moist.

Hot, dry spells can make the flowers drop without setting pods. Watering at flowering time helps. Dwarf beans don't need a support, though a few twiggy sticks keep heavy plants and their pods off the soil.

The first pods are ready about eight to ten weeks after sowing. Pick them young, when they are pencil-thin, about 6–8 in long for most varieties, and snap cleanly. Pick every few days: the more you pick, the more the plants set, and pods left to swell turn stringy.

Raw beans contain lectins, mainly phasin, that cause vomiting and diarrhoea, and a handful can be enough. Cooking destroys them, so always cook green beans, never eat them raw from the plant.

When the plants stop cropping, cut them at soil level and leave the roots in the ground.

Bean seed fly maggots eat germinating seeds, leaving gaps or blind, stunted seedlings. It is worst in cold, wet soil and where fresh compost went in just before sowing. Sow into warm soil, raise plants in pots, or cover the row with fleece or fine mesh.

Slugs go for the young seedlings, and black bean aphids colonise shoot tips. Rust shows as small brown to black pustules under the leaves, usually after midsummer and too late to hurt the harvest much.

Halo blight and anthracnose cause spots on leaves and pods and are carried on the seed. Use fresh, healthy seed and don't save seed from spotted pods.

French beans are legumes. Don't follow them with peas or other beans; leave three to four years before legumes return to the bed.

Summer savory is the classic partner for beans in German gardens and is said to keep black bean aphids away. We found no trials that back this up; it's tradition, but a harmless and tasty one.

What makes sense: dwarf beans are short and quick, and their roots leave some nitrogen behind for the next crop. Keep other legumes out of the rotation for the reasons above.