When to start spinach seeds

Spinach is a direct-sow crop. It takes the place of a duplicate kale entry in our original list of guides.

Direct sowing is the standard method

University of Minnesota Extension sows spinach directly as soon as the soil is workable in spring. For a continuous supply, sow again every one to two weeks until outdoor temperatures reach 80°F. Plant seeds a quarter to half an inch deep in rows 18 to 30 inches apart, and thin to 2 to 4 inches apart. A floating row cover protects seedlings from cold and insects; once it warms up, swap it for a lightweight mesh that still keeps out flea beetles and leaf miners.

Germination in cold soil

Spinach is one of the few crops that sprouts in near-freezing soil. Harrington's data (published by Oregon State Extension) list a 35°F minimum, a 45–75°F optimum range and an 85°F maximum. Seedlings appeared in about 62 days at 32°F, 22 days at 41°F, 12 days at 50°F, 7 days at 59°F and 6 days at 68°F, with little or no germination at 95°F. Early spring sowings are slow but they work; midsummer sowings into hot soil often fail.

Starting indoors (optional)

University of New Hampshire Extension gives spinach 4 to 6 weeks from seed to transplant and says it is safe to set out 3 to 6 weeks before the last frost. With an average last frost of May 10, you would sow indoors February 15 to March 1 and set plants out March 29 to April 19. Transplants give an earlier, evenly spaced crop, but for a fast, inexpensive crop like spinach, direct sowing is usually simpler.

Bolting: day length matters

UMN notes that spinach is day-length sensitive: as days lengthen in late spring, plants bolt to seed and the harvest ends. That is why spring sowing should start early, and why a summer gap is normal. Swiss chard is not day-length sensitive, which makes it a useful summer substitute.

Fall spinach

For a fall crop, UMN suggests sowing about two months before the average first fall frost. Spinach sown in August grows under shortening days and does not bolt. In warm areas, wait until summer heat breaks; UMN advises mid-August or later in most of Minnesota. The fall planting calculator can check a specific variety's timing.

In mild-winter areas, spinach is grown through fall and winter instead of spring. The UF/IFAS Florida Vegetable Gardening Guide, for example, lists fall and winter planting windows for spinach.

Common mistakes

• Sowing too late in spring. Lengthening days trigger bolting.
• Sowing into hot soil. Germination fails at high soil temperatures.
• One sowing only. Small sowings every 1–2 weeks give a longer harvest.
• Skipping fall. Fall-sown spinach grows under shortening days and doesn't bolt.