How to Grow Spinach

Spinach is one of the hardiest garden greens. Maryland Extension says it can withstand heavy frosts in spring and fall, and NC State says it survives temperatures down to about 20°F. UW-Madison puts its ideal weather at 50 to 60°F. Its weakness is day length. As days lengthen in late spring, spinach switches from making leaves to making seed.

When to plant

Spinach is one of the first crops in the ground. Sources give slightly different timing:

• Utah State: sow 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 you prepared the bed the previous fall, you can scatter seed over frozen ground or snow in late winter and it will germinate as the soil thaws.

Utah State and the University of Arizona say seed germinates once the soil reaches 40°F. Maryland and UW-Madison say 45°F. Utah State gives 55 to 65°F as the best range, with seedlings emerging in 7 to 10 days, while UW-Madison lists a 70°F optimum. Above 80°F, germination falls off (Utah State). Start from the dates for your zone above.

Transplants are optional. Utah State grows them for 5 to 6 weeks and sets them out near the last frost. Sow again every 2 weeks (UW-Madison) for a longer harvest, and switch to slow-bolting varieties for the later sowings.

For fall, Utah State sows early varieties 50 to 75 days before the target harvest date, timed to mature 1 to 2 weeks after the first fall frost. Illinois suggests chilling seed in the refrigerator for 1 to 2 weeks before summer or fall sowings. UW-Madison finds fall crops often taste better.

Sowing, spacing and soil

Sow seed about 1/2 inch deep (Utah State, Illinois, UW-Madison), around 12 to 15 seeds per foot (Illinois), in rows about 12 inches apart. Thinning advice varies: Utah State and the University of Arizona thin to 3 inches, Illinois to 2 to 4 inches in rows or 4 to 6 inches in beds, and NC State to 2 to 3 inches. Maryland thins again in early summer by cutting every other plant, leaving about 6 inches between them. Thinnings are good to eat.

Spinach wants fertile, well-drained soil rich in organic matter. It’s a weak competitor, so pull small weeds early and cut larger ones at the soil line instead of digging near the shallow roots (UW-Madison).

Water and feeding

Give spinach 1 to 2 inches of water a week (Utah State). Uneven moisture makes leaves tough and off-flavored. UW-Madison adds that dry, infertile soil pushes spinach to bolt sooner. Mulch helps hold moisture and keeps rain from splashing soil onto the leaves.

Sources differ on fertilizer. UW-Madison calls spinach a heavy feeder. It fertilizes before planting and sidedresses when plants are about 2 inches tall, which matters most in spring, when cold soil holds back nitrogen. Utah State applies 1/4 cup of 21-0-0 per 10 feet of row at thinning or 4 weeks after transplanting. Illinois says plants in ample moisture and fertile soil need no extra fertilizer. It sidedresses with nitrogen only if growth is slow or the leaves are pale.

Bolting and varieties

Long days in late spring trigger the seed stalk, and warmth speeds it up. Once a plant starts to bolt, leaf quality drops quickly, so harvest the whole plant (Illinois). Slow-bolting varieties buy you time but not the whole summer. UW-Madison notes that even these don’t stay leafy for long in summer heat and long days. The old rule that prickly-seeded types suit spring and fall and round-seeded types suit summer no longer holds, because slow-bolting round-seeded varieties now exist (UW-Madison).

Savoy (crinkled) leaves are thicker but trap soil. Smooth leaves are easier to clean (UW-Madison, Maryland). Extension services recommend these varieties for their regions:

• Wisconsin (UW-Madison): ‘Melody’ for spring or fall; ‘Olympia’ for spring and early summer; ‘Bloomsdale Long Standing’, which often overwinters with mulch; ‘Space’, ‘Tyee’ and ‘Acadia’ for downy mildew resistance.
• Utah (Utah State): ‘Bloomsdale’, ‘Melody’, ‘Teton’, ‘Olympia’.
• Florida (UF/IFAS): ‘Melody 3’, ‘Bloomsdale Longstanding’, ‘Tyee’, ‘Space’.
• Texas (Texas A&M): ‘Bloomsdale’, ‘Early Hybrid’, ‘Melody’.

Overwintering

Spinach is one of the few greens that can bridge winter in cold climates. Utah State says plants with 4 to 5 true leaves by late fall overwinter easily under a heavy mulch, which you remove after the snow melts. UW-Madison offers another approach: cut the leaves off a fall crop but leave the roots and growing point, and the plants may regrow in spring. Illinois adds that low tunnels and cold frames give winter salads. Maryland says that with protection, fall spinach can be harvested into December.

Regional notes

In the North and the Mountain West, sow as early as the soil allows in spring and plan a fall crop too. In the Pacific Northwest, WSU Extension in Skagit County lists spinach as hardy in the region’s cool weather but stresses choosing a bolt-resistant variety. In the humid Southeast and Mid-Atlantic, watch for downy mildew, which Illinois says is worst in wet, humid seasons. It recommends resistant varieties and raised beds for drainage. In warm-winter areas such as Florida, south Texas and the Arizona low desert, spinach is strictly a crop for the coolest months, from fall through winter. UF/IFAS suggests New Zealand spinach, Malabar spinach or Swiss chard for summer greens. Your months are in the dates for your zone above.

Pests and problems

• Spinach leafminer. Maggots tunnel inside the leaves, leaving pale trails. Remove mined leaves, because sprays don’t reach larvae inside the leaf. To prevent damage, cover plants with row cover after thinning. UW-Madison says to hold the fabric up on hoops, since tender spinach leaves bruise if the cover rubs them in wind.
• Downy mildew. Worst in wet, humid seasons. Grow resistant varieties and use raised beds.
• Blight. Illinois uses this name for cucumber mosaic virus in spinach, which causes yellowing, stunting and early death. Resistant varieties are the fix.
• Aphids. Hose them off, remove infested leaves, or leave them to lady beetles and lacewings.
• Slugs. UW-Madison says to skip mulch where slugs are a problem.

Harvest and storage

Start picking when the plant has a rosette of at least 5 or 6 leaves (Illinois; UW-Madison says 6 true leaves). Take outer leaves and the center keeps producing, especially in fall. Cutting whole plants at the soil line keeps leaves cleaner. Utah State says all leaves can be cut to within 2 inches of the soil if the growing point is undamaged. Harvest everything once a seed stalk appears.

Expected yields vary widely: Utah State gives 4 to 6 pounds from a 10-foot row, while Maryland gives about 2 pounds. Near 32°F and high humidity spinach keeps 1 to 2 weeks (Utah State) or 2 to 3 weeks (Maryland). In a home refrigerator, UW-Madison suggests about a week. NC State notes that raw spinach contains oxalates, which reduce how much iron and calcium the body absorbs.