Spinach

Spinach (Spinacia oleracea) is a fast-growing, cool-season annual in the amaranth family, native to a region stretching from central Asia to southwest Siberia. It’s a hardy crop that can survive 20 °F (−7 °C) without injury, so it suits spring and fall. The catch is that long days and heat make it bolt, so sowing early enough matters more than with most leafy greens.

There are smooth-leaved and crinkly savoy types; flat-leaved varieties tend to cope better with warm weather than savoy ones. Several other plants are called spinach because they’re used the same way, but many are unrelated, and some handle summer heat better.

When to sow. Spinach germinates best in cool soil, so start sowing in early spring as soon as the ground can be worked, once the soil has reached about 45 °F (7 °C). Sources differ on exact timing: gardening experts suggest sowing 4–8 weeks before your average last spring frost, while gardening experts suggest 2–3 weeks before. Sow again from late summer to early fall for an autumn crop, choosing hardy varieties if you want plants to overwinter. Soil above 85 °F (29 °C) holds back germination.

How to sow. Sow directly outdoors, because transplanting can make spinach more likely to bolt. US sources recommend sowing ½ inch (13 mm) deep, while gardening experts sow in a drill 1 inch (2.5 cm) deep. Seedlings usually appear in 7–10 days. Use fresh seed: spinach seed more than a year old doesn’t germinate well.

Spacing. Thin seedlings to 2–3 inches (5–7.5 cm) apart; full-size plants need 4–6 inches (10–15 cm). Crowded plants are more likely to get downy mildew.

Site and soil. Spinach grows best in moist, rich, well-drained soil in full sun to partial shade, and some shade helps in hot weather. It’s sensitive to acidic soil, so aim for a pH between 6.0 and 7.0.

Pots. Gardening experts say spinach can grow in containers as small as 1 gallon (about 4 L) and 4–6 inches (10–15 cm) deep. Gardening experts recommend a larger pot, at least 30 cm (1 ft) wide and deep, so the compost doesn’t dry out too fast.

Watering. Spinach needs a steady supply of moisture. Gardening experts call it a thirsty crop: dry soil interrupts growth and leads to bolting. Water in the morning and aim at the soil rather than the leaves, since wet foliage encourages fungal disease. A mulch keeps the soil moist and cool.

Bolting. Longer days and summer heat make spinach send up a flower stalk, which stops leaf growth and turns the leaves bitter. Spinach tends to bolt once temperatures reach about 80 °F (27 °C), and that day length alone can trigger it even in cool weather. Shade cloth helps once days warm to about 70 °F (21 °C). For spring crops in warm climates, choose bolt-resistant varieties.

Weeds. Weed shallowly, since deep cultivation damages the roots, and don’t pile soil against the plants, because buried leaves rot quickly.

Winter. Spinach can overwinter for an early spring crop if plants have 4–5 true leaves by late in the year; mulch them heavily and remove the mulch once the snow melts. Unless your climate is mild, cover overwintering plants with cloches or fleece from October.

Insect pests include aphids, cutworms, cabbage loopers, corn earworms and diamondback moth caterpillars. Aphids matter most because they spread viruses. Slugs and snails like the soft young leaves, and birds may eat seedlings. Row covers keep out spinach leaf miners.

The main diseases are downy mildew, white rust and damping-off of seedlings; resistant varieties help avoid downy mildew. Downy mildew takes hold most easily in humid weather and when plants are crowded.

You can pick baby leaves about a month after sowing and mature leaves after about two months; gardening experts expect spinach to be ready in about 37–45 days. Pick the outer leaves first and let the younger ones keep growing. As long as the growing point isn’t damaged, you can cut all the leaves to about 2 inches (5 cm) above the soil and let the plant regrow. Once plants start sending up flower stalks, make a final harvest.

Rinse and dry the leaves, then keep them in plastic bags in the refrigerator. Fresh leaves only last a few days in a home fridge, so pick what you need and freeze spinach for longer storage. In very cold, humid storage (32 °F/0 °C, 95% humidity) it keeps for one to three weeks.

Raw spinach is safe to eat, but it contains oxalates, which can reduce how much iron and calcium the body absorbs. Cooking it in several changes of water lowers the oxalate level. Gardening experts note this is a concern only with large amounts over time or a low calcium intake.