Spinach grows best in the cool weather of spring and fall. Mature spinach plants can tolerate temperatures as low as 10 to 20°F (-12 to -7°C).
Time spinach seed sowing so plants come to harvest before or after the very warm and hot weather of summer. Hot weather will trigger bolting and seed-stalk formation. Bolting can be slowed by picking the oldest leaves first, but bolting ultimately can not be stopped if spinach is matures in very warm weather.
Spinach matures in 35 to 50 days depending on the variety.
Sowing and Planting Tips:
- Spinach seed is viable for 3 years.
- Spinach is grown from seeds or transplants.
- Direct-sow spinach seeds in the garden 6 to 4 weeks before the last spring frost; spinach can be started indoors a couple of weeks earlier.
- Sow seed ½ inch (13mm) deep.
- Sow seeds 1 inch (2.5cm) apart; later thin seedlings to 6 inches (15cm) apart; use the thinnings in salads. Make sure there is good air circulation around seedlings and maturing plants to avoid disease.
- Space plants 6 to 9 inches (15-22 cm) apart in a staggered pattern or in rows 11 to 18 inches apart.
- Spinach grows best in full sun but can tolerate light shade.
- Spinach prefers a soil pH between 6.5 and 7.5.
- Seed germinates in 7 to 14 days at or near 70°F (21°C)—but sometimes seed can take up to 3 weeks to germinate in cold soil.
- When sowing seed in summer for fall harvest, first place the seed in a folded damp paper towel placed in a plastic bag and kept in the refrigerator for 5 days before sowing.
- Keep the soil evenly moist until seeds germinate then keep the soil moist until seedlings are well established; once plants are established mulch with straw to keep the roots cool and moist.
- Add aged compost to planting beds in advance of sowing; compost will feed the soil and aide moisture retention.
- Spinach grows best when daytime temperatures are in the 60s°F (mid- to high teens °C).
- Spinach can tolerate light frosts in the spring and freezes in the fall.
- Spinach planted in the fall can winter over under straw and a floating row cover and will begin new growth early in spring.
- Avoid planting spinach where beets, chard, or orach has recently grown. Plant spinach where beans have just grown if you can.
- Make successive sowings every few weeks for an extended harvest.
- Fertilize with an organic fertilizer such as fish emulsion at half strength.
- Aphids and leaf miners can attack spinach.
- Cut plants back to about 3 inches (7 cm) above the soil in late summer; the plant will produce new leaves for autumn harvest.
Interplanting: Interplant spinach with carrots, radishes, strawberries.
Container Growing: Choose a container 4-6 inches (10-15 cm) deep.
Recommended Planting Calendar:
- 12-10 weeks before the last frost in spring: direct sow in plastic tunnel or cold frame for spring crop.
- 8-6 weeks before the last frost: direct-sow in the garden then succession sow every 3 weeks until temperatures rise into the high 70°sF (mid 20°sC).
For fall and winter crop:
- 8-6 weeks before the first frost in fall: direct-sow in the garden.
- 6-4 weeks before the first frost in fall: direct sow in plastic tunnel or cold frame for fall and winter harvest.
- 5-4 weeks before the first frost in fall: direct sow in the garden to overwinter for early spring harvest; this crop should be covered with shredded leaves for straw and a floating row cover before freezing weather arrives; remove the cover and mulch in early spring to allow plants to continue growth.
Recommended Varieties: Smooth leaf varieties: ‘Bordeaux’ green leaves with red veins, bolts easily in hot weather; ‘Olympia’ grows best in early spring; ‘Space’ is slow to bolt; ‘Whale’ is mildew and bolt resistant. Semi-savoyed and savoyed leaf varieties: ‘Bloomsdale Longstanding’ thick and crinkled leaves; ‘Melody’ slow to bolt, crinkled leaves; ‘Tyee’ slow to bolt, crinkled leaves.
Botanical Name: Spinacia oeracea
Spinach belongs to the Chenopodiaceae family, other members include beets, chard, quinoa, and sugar beets.