When to Plant Spinach

Spinach is planted early because of day length, not because of frost. Maryland Extension calls it a hardy annual that withstands heavy frost in spring and fall. What ends the crop is the long days of late spring, which trigger a seed stalk, with warm temperatures speeding things up. Plant so the leaves are ready before that happens, or plant in late summer so the crop matures as days shorten. The dates for your zone above put this on a calendar.

Spring: as early as the soil allows

Sources agree that spinach goes in well before the last frost. They differ on the exact lead time:

• Utah State: 2 to 3 weeks before the last frost. Elsewhere it says seed can go in 3 to 4 weeks ahead of transplanting time.
• UW-Madison: about 4 weeks before the last frost.
• Illinois: as soon as the soil is prepared. If the bed was prepared the previous fall, you can broadcast seed over frozen ground or snow in late winter and it will sprout as the soil thaws.

Soil temperature is the practical test. Utah State and the University of Arizona say spinach germinates once the soil reaches 40°F. Maryland and UW-Madison use 45°F. Seed comes up in 7 to 10 days at 55 to 65°F (Utah State). Colder soil works but is slower. Take soil readings at a depth of 2 inches.

Transplants are rarely needed. Utah State says they take 5 to 6 weeks to grow and go out near the last frost date. For a longer harvest, UW-Madison sows every 2 weeks and switches to slow-bolting varieties as spring goes on. Even those won’t stay leafy for long once summer’s long, hot days arrive.

Why late-spring sowings fail

Spinach sown too late in spring has little time to grow before day length triggers bolting. Utah State notes that soil above 80°F also cuts germination. UW-Madison adds that dry, infertile soil makes plants bolt sooner, so late sowings need steady water and nitrogen. If you sow after mid-spring, choose a variety labeled long-standing or slow-bolting.

Fall: time it to finish after the first frost

Fall is often the best spinach season. UW-Madison says the fall crop often tastes better because the weather is more predictable. Utah State’s method is to choose early varieties and sow 50 to 75 days before your target harvest date, timed for the crop to mature 1 to 2 weeks after the first fall frost. Plants can stay in the garden through light frosts.

Late-summer soil is often too warm for good germination. Illinois suggests chilling the seed in the refrigerator for 1 to 2 weeks before summer or fall sowings. Shade the seedbed and keep it moist until seedlings are up.

Maryland says fall spinach can be harvested into December with protection such as row covers.

Overwintering for the earliest spring crop

In much of the country, a well-timed fall sowing can carry through winter and give the first greens of spring:

• Utah State says plants need 4 to 5 true leaves by late fall to overwinter easily. Mulch them heavily and pull the mulch back after the snow melts.
• UW-Madison says a “winter” crop sown in early fall grows a little before going dormant. Another option is to cut the leaves off a fall crop, leaving the roots and growing point, and let it regrow in spring. Mulch improves survival in colder areas. ‘Bloomsdale Long Standing’ is among the hardier varieties, according to UW-Madison.
• Illinois notes that in southern locations young plants survive winter on well-drained soil without help. Elsewhere, mulch, low tunnels and cold frames make the difference.

Warm-winter areas

In zones 9 to 11, spinach grows only in the coolest part of the year. UF/IFAS plants it only in fall in North Florida, from fall through winter in South Florida, and into early spring in Central Florida. The University of Arizona’s Maricopa County calendar seeds in the Phoenix low desert from early fall into winter. Texas A&M recommends sowing in the Lower Rio Grande Valley from mid-fall to midwinter. For greens after the season ends, UF/IFAS suggests New Zealand spinach, Malabar spinach or Swiss chard. Your exact months are in the dates for your zone above.