Potatoes (Solanum tuberosum) are grown from seed tubers – buy certified ones, as saved tubers often carry viruses. Four to six weeks before planting, set the tubers in trays in a bright, cool room at 10–15 °C to chit; short, sturdy green shoots speed up emergence and increase early yields. Plant in April, once the soil has warmed to about 8 °C, 8–10 cm deep and 30–35 cm apart in rows 60–70 cm apart. Potatoes prefer loose, light to medium soil that is slightly acid (pH 5.5–6.5); lime encourages common scab. When shoots are 15–20 cm tall, draw soil up around them into ridges, and repeat once or twice – this keeps light off the tubers, which would turn them green and toxic. Colorado beetle and late blight are the main problems; pick off beetles and larvae and remove blighted foliage promptly. Dig early varieties in July while the plants are still green; leave maincrops until the foliage dies back, then store them in the dark at 4–6 °C.