Spinach (Spinacia oleracea) is a quick leafy crop for the cool parts of the year: in warm weather and long days it runs to seed and the leaves turn bitter. Sow directly outdoors in March and April, 2 cm deep in rows 25 cm apart, and again from mid-August to September for an autumn harvest; hardy varieties sown in September can overwinter and crop early the next spring. Spinach needs rich, moisture-retentive soil with pH 6.5–7.5 and plenty of nitrogen, but avoid heavy nitrogen feeding shortly before harvest, as the leaves accumulate nitrates. Keep the soil evenly moist and give light shade in warm spells. Downy mildew causes yellow patches on the leaves in damp weather; resistant varieties and wider spacing help. Start harvesting after about six to eight weeks, picking the outer leaves or cutting whole rosettes before a flower stalk appears. Young leaves are excellent raw in salads; larger ones are best cooked briefly and freeze well.