Overwintering Spinach on a Small Farm for Early Spring Cuts

Every spring the same gap shows up at market: customers want greens in March, and your first sowings will not be ready until May. Overwintering spinach closes that gap, because a planting that goes in during early fall can sit dormant through the cold and then grow fast the moment days pass ten hours of light.

I have grown overwintered spinach in zone 5 and zone 6 for years, on open ground and under cover. It is one of the few crops where the timing matters more than the variety, the soil or the fertilizer. Get the sowing date right and most of the work is done.

How overwintering spinach actually works

Spinach is a cold tolerant plant. Established leaves survive air temperatures down to about 15 F without cover, and the crown can live through colder spells than that if the soil does not heave. What it cannot handle is going into winter too small or too large.

The target is a plant with four to six true leaves, roughly the size of your palm, by the time daylength drops below ten hours. In most of the northern United States that happens in mid November. A plant that size has enough root to anchor itself and enough leaf to restart in spring, but not so much soft growth that wind and freeze cycles shred it.

Once daylength drops under ten hours, which growers call the Persephone period, spinach barely grows no matter how warm a cover keeps it. That is why overwintering is a holding strategy, not a winter harvest. You are storing a crop in the field.

Sowing dates by zone

Count back from your average first hard frost, meaning the first night around 28 F. Spinach needs about four to six weeks of decent growing weather to reach that palm size.

If you have missed the window this year, you can still sow in a tunnel up to two weeks late. Expect smaller plants and a later spring cut, but most of them will survive.

Varieties and seeding rates

Pick a savoy or semi-savoy type bred for cold. 'Winter Bloomsdale', 'Giant Winter' and 'Space' have all done well for me. The crinkled leaves of savoy types hold up better to freeze and thaw than the flat smooth-leaf types sold for baby greens.

Sow at about 12 to 15 seeds per foot of row, half an inch deep, in rows 12 inches apart on a 30 inch bed. That works out to roughly 1 ounce of seed per 100 feet of row. Thin to 2 to 3 inches apart once the first true leaves show. Crowded plants rot at the crown over winter because air cannot move between them.

Spinach germinates poorly in warm soil. Above 75 F, germination falls off sharply. For August sowings, I soak seed for two hours, sow in the evening, and lay a board or burlap over the row for three days to keep the soil cool and moist. Check daily and pull the cover the moment you see hooks.

Soil and fertility before the cold

Overwintered spinach wants a well drained bed more than anything. Standing water in January will kill more plants than cold will. If your field holds puddles after a heavy rain, pick a slightly higher bed or skip this crop on that ground.

Keep fall nitrogen modest. About 1 to 1.5 pounds of actual nitrogen per 1,000 square feet at sowing is plenty. Heavy fall feeding produces soft, lush leaves that freeze badly. Spinach also hates acid soil and will yellow below a pH of about 6.2, so if you have not tested lately, check before sowing. Our piece on liming acid soil on a small farm covers how much lime to add and when.

Why you should not mulch spinach heavily

A lot of advice says to bury overwintering spinach under several inches of straw once the ground freezes. I stopped doing this after two seasons of losses.

Thick straw holds moisture against the crowns, and on mild winter days it turns into a damp, dark blanket that invites rot. It also hides voles, which will happily eat their way down a row under cover where no hawk can see them. In my notes, the straw mulched rows lost 30 to 40 percent of plants by March, while the uncovered rows next to them lost around 10 percent.

What works better is a light layer of breathable cover. Floating row cover at 1 ounce per square yard adds about 4 to 6 F of protection and still lets the leaves dry out between storms. If you already have hoops up, our guide to extending your growing season with a low tunnel shows how to vent it on sunny days. In zone 4 or on windy ridges, a tunnel over row cover is worth the effort. Straw only makes sense if you have no cover at all and expect long stretches below 10 F with no snow.

Managing the crop through winter

Winter care is mostly about leaving it alone. A few jobs still matter:

• Vent tunnels above 50 F. A sealed tunnel on a sunny January day can climb past 80 F inside, which softens the leaves right before a hard night.
• Do not harvest frozen leaves. Picking spinach while it is frozen ruptures the cells. Wait until midday when the leaves have thawed and gone limp, then firm again.
• Weigh down cover edges. Sandbags every 6 to 8 feet keep wind from peeling covers back, which is how most winter losses happen.
• Watch for heaving. After a freeze and thaw cycle, press lifted crowns back into the soil by hand.

Spring harvest and when to replace it

Growth restarts in late February to early March in zone 6, once days pass ten hours and soil warms toward 40 F. Side dress with a fast nitrogen source such as fish emulsion or blood meal at that point, and the plants will put on new leaves almost weekly.

Cut outer leaves first, leaving the center to keep producing. You can usually get three to five cuttings before the plants bolt in April or May as days lengthen. A 100 foot row typically yields 40 to 60 pounds over that span, and early spring spinach sells for $8 to $12 a pound at many farmers markets because almost nobody else has it.

Plan your next crop to follow on that bed once the spinach bolts. It fits neatly into a rotation, as explained in succession planting without a spreadsheet.

Frequently asked questions

Can spinach survive winter without any cover?

In zone 6 and warmer, established spinach often survives uncovered, especially with snow cover. In zone 5 and colder, losses go up sharply without at least a layer of row cover. Wind exposure matters as much as temperature, so a sheltered bed may survive where an open one fails.

When should I plant spinach to overwinter?

Sow four to six weeks before your average first hard frost, so the plants have four to six true leaves by mid November. In zone 5 that usually means the last week of August through mid September. Late sowings can still work under a tunnel, but harvest starts later.

Why is my overwintered spinach bolting so fast?

Spinach bolts in response to long days, and overwintered plants are already mature when spring arrives. Once daylength passes about 14 hours, flowering is nearly impossible to stop. Harvest hard in March and April and sow a fresh spring crop as a follow on.