How to Grow Spinach from Seed
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How to grow spinach from seed comes down to four decisions: when to sow, how deep to cover the seed, how to thin the seedlings, and how to keep the crop from running to seed in warm weather. The extension pages we opened agree on most of the basics, but they give different depths, spacings and thinning heights. This guide sets each stated figure beside its source, points out where the sources disagree, and marks the questions they leave open.
Quick answer
- Cover spinach seed about one-quarter to one-half inch deep. Illinois Extension gives one-half inch.
- Thin the seedlings so each plant has room to grow. The sources give 2 to 4 inches, or 2 to 3 inches, depending on the guide.
- Spinach bolts when days get long and the weather warms, so sow early in spring and again in fall, and pick slow-bolting varieties for later sowings.
- Starting indoors is an option. NC State Extension suggests starting indoors eight weeks before the first frost for transplants.
Choose a variety that suits your season
Spinach is a cool-season crop, and the variety you choose decides how long it stays in leaf before it runs to seed. The Wisconsin guide describes the plant’s habit in one plain line: the plant grows a rosette of dark green leaves, but “under warm temperatures and long day length it bolts and goes to seed.” Because bolting depends on both heat and day length, the variety and the sowing date work together.
The Wisconsin guide notes that some newer varieties are slow to bolt, and it recommends bolt-resistant varieties for later plantings. Its advice is that even slow-bolting types will not stay leafy for long in warm weather. The Illinois guide makes a similar split by season: varieties that are long-standing, or slow to bolt, are best suited to spring planting.
Seed quality also matters. The Wisconsin guide says spinach seed does not remain viable for very long, so buy seed packaged for the current year. Stored under cool conditions with low humidity, seed can stay viable for a couple of years, but the Wisconsin guide says germination rates will typically be reduced.
When to sow
Timing is where the sources are most specific. The Wisconsin guide says spinach is a cool-season crop that is “best planted in early spring, about 4 weeks before the average date of last frost.” It also gives an ideal temperature for the growing crop: “Ideal spinach weather is 50 to 60 °F.” Those two figures point in the same direction. The cool-season habit the Wisconsin guide describes points to early spring and fall, not midsummer.
NC State Extension describes two windows. For spring crops, you can plant seed directly in the soil in early spring, or start indoors eight weeks before the first frost for a later transplant. For fall crops, it advises that you “start plants indoors early, or directly sow seeds after the hottest heat of summer has passed.” The same guide says plants are somewhat frost tolerant and “can survive temperatures down to 20 degrees F,” which is useful for deciding whether a late-season row is worth covering. It does not say how much protection to give, so treat the 20-degree figure as a limit on tolerance, not a plan for cold nights.
The Illinois guide adds a method for late winter. If the soil was prepared in the fall, the guide says “seeds can be broadcast over frozen ground or snow cover in late winter and they will germinate as the soil thaws.” The guide does not say how early in spring this works in your area. Only the Illinois guide mentions chilling seed, and it limits that advice to summer and fall plantings: “Chill seeds for summer or fall plantings in the refrigerator for 1 or 2 weeks before planting.” Because only one source raises it, treat chilling as an optional step rather than a required one.
Sow the seed
Spinach seed goes in shallow. Illinois says “Cover 1/2 inch deep.” NC State says to plant seeds “¼ to 1/2 inch deep and thin seedlings to 2 to 3 inches apart.” The Wisconsin guide says to plant seeds about one-half inch deep. A depth of about one-half inch is the common figure across the three extension guides, and the NC State range allows a little shallower.
Sowing density is where the guides differ most in style. Illinois says to “Sow 12 to 15 seeds per foot of row,” and its guide notes that rows may be as close as 12 inches apart, depending on how you keep the weeds down. Wisconsin suggests planting seeds “1 to 4 inches apart” and then thinning if you use the closer spacing. Both approaches expect you to thin afterwards.
The UNH fact sheet says that “Water, oxygen, light, and heat can all affect germination.” The USU guide on starting seed indoors says that “Most plants you sow will readily germinate at soil temperatures between 65 °F – 75 °F.” That is a general figure for most seeds, not a spinach figure, and the spinach guides do not give a germination temperature for spinach itself. For moisture, the UNH fact sheet says that “A continuous supply of moisture without fluctuation in the growing medium is important to ensure germination.” Plan watering so the seedbed does not swing between dry and soaked.
Thin the seedlings
Thinning is the step that most often decides how good the harvest looks. Illinois gives the clearest timing: “When the plants are one inch tall, thin to 2 to 4 inches apart.” NC State says thin seedlings to 2 to 3 inches apart without giving a height. Wisconsin ties thinning to the seedlings’ size instead: if you use the closer spacing, thin “when the plants are about 2 inches tall.” Its wording also offers the cue “thin when the leaves touch.”
You do not have to thin at all if you plan to harvest whole plants. The Illinois guide says “Closer spacing (no thinning) is satisfactory when the entire plants are to be harvested.” That fits a row you plan to cut as whole plants.
The thinnings are not wasted. Illinois says “Late thinnings may be harvested as whole plants and eaten.” The Wisconsin guide also suggests using the tender leaves of the thinnings for salad greens. Pick them while the leaves are small and soft.
| Source | Sowing depth | Spacing or thinning | Thinning height |
|---|---|---|---|
| Illinois Extension | Cover 1/2 inch deep | Thin to 2 to 4 inches apart | When plants are about 1 inch tall |
| NC State Extension | 1/4 to 1/2 inch deep | Thin to 2 to 3 inches apart | Not stated |
| University of Wisconsin Extension | About 1/2 inch deep | Seed 1 to 4 inches apart; thin for closer spacing | About 2 inches tall |
The table shows where the sources agree and where they do not. All three give a shallow sowing depth, and all three expect you to thin. They differ on the final spacing and on when to thin.
Start indoors if the spring is short
Most of the sources describe direct sowing as the main method, with indoor starts as an option NC State describes for spring and fall crops. NC State gives the indoor timing: start eight weeks before the first frost for a later transplant. The sources we opened do not say how well spinach handles transplanting, so the direct-sow method is the one with the clearest guidance behind it.
If you do start indoors, the University of Maryland Extension guide gives a container size for this crop. It lists “Lettuce, beets, spinach, kale, and other greens – 3 to 6 square inches” as the recommended cell size for a seed-starting tray. The Maryland guide explains that individual cells keep roots from tangling with neighboring plants as they grow, and that the connected tray makes moving plants around as a group easier.
The same Maryland guide makes two points about the setup. It says “Care must be taken to avoid overwatering undrained flats,” so every tray needs drainage or a way to empty the water that collects. It also says “Natural light from a window is seldom enough for strong seedling growth,” which means a sunny windowsill is usually not bright enough on its own. The same guide notes that “Plant stems usually stretch and lean towards the light, which can result in weak plants,” which is one reason to plan for a grow light.
Keep the crop from bolting
Bolting is the stage when the plant sends up a flower stalk and the leaves turn bitter. The Illinois guide says plainly that “Spinach bolts quickly to seed during the long days in late spring or summer.” NC State recommends that growers in warm climates use “bolt-resistant cultivars” for a spring crop, and the Wisconsin guide says the same for later sowings. The variety and the sowing date work together, which is why the guides pair slow-bolting varieties with spring sowing.
The guides also differ on how long to keep sowing. The Illinois guide advises that you “Plant successive crops for several weeks after the initial sowing to keep the harvest going until hot weather.” The Wisconsin guide goes further and recommends “Make sequential plantings about 2 weeks apart to continue harvesting spinach through the summer,” but only with bolt-resistant varieties for the later rows. Both approaches use sowing in small batches. The difference is whether you expect the planting to continue into summer at all.
Insect pressure is the other concern in the Wisconsin guide. It says “To prevent leaf miner damage, cover plants with floating row covers after thinning.” The same guide describes the leaf miner as a fly that lays its eggs on the undersides of the leaves. It adds that “Use supports, such as hoops, to keep the fabric off of the plants.”
A quick reference for your planting calendar
The figures below are the ones the sources state directly. Use them as a check against your local last-frost date, which none of the pages we opened gives for your area.
| Practice | Figure the source states | Source |
|---|---|---|
| Spring sowing | About 4 weeks before the average last frost | Wisconsin |
| Indoor start for transplant | Eight weeks before the first frost | NC State |
| Sowing density | 12 to 15 seeds per foot of row | Illinois |
| Repeat sowings | About 2 weeks apart through summer | Wisconsin |
| Cell size for greens indoors | 3 to 6 square inches | University of Maryland |
| Seed storage | Viable for a couple of years, with lower germination | Wisconsin |
For a wider look at which crops fit a raised bed, see easiest vegetables to grow in raised beds. For spacing and neighbors in the same bed, see raised bed companion planting and layout.
How we chose
The pages we opened on 2026-10-23 are university extension guides from Illinois, Wisconsin, NC State, Maryland and Utah State, plus a fact sheet from the University of New Hampshire. We kept the figures that a page states in plain words, either about spinach or about starting seed in general. We marked the general figures as general. We did not use seed-company listings, blog posts or forum answers for any figure in this guide. We also did not rank varieties or name products, because none of the pages we opened gave a basis for a recommendation.
What we could not verify
Some extension pages did not load from our connection, including a Penn State spinach guide. Their guidance is not in this article. The pages we did open differ on depth and thinning height, and this guide does not pick a single correct figure. Where the table shows two numbers, both are the source’s own figure, not our estimate.
What the sources do not say
None of the pages we opened gives a days-to-harvest figure for spinach that you could use to plan a specific bed. Wisconsin lists maturity figures for some named varieties, but those are variety figures, and the guide does not give a rule for every variety. No page gives a local frost date, so the timing advice is relative to the last frost in your area, not a calendar date. The sources also do not say how much cold a spinach seedling can take when it is small, or how to protect a fall crop through a hard freeze. The NC State figure of 20 degrees F is a limit on tolerance, not a protection plan, and this guide does not turn it into one.
Frequently asked questions
Is fall sowing an option for spinach seed?
Yes, according to the NC State guide, which describes fall crops as ones you start indoors early or sow directly “after the hottest heat of summer has passed.” The Wisconsin guide describes 50 to 60 °F as ideal spinach weather. The guide does not give a fall date for your area, so check your local calendar before you sow.
How deep should spinach seed be planted?
Plant it shallow. Illinois says to cover the seed one-half inch deep, NC State gives a range of one-quarter to one-half inch, and Wisconsin says about one-half inch.
How far apart should spinach plants be?
The sources give 2 to 4 inches after thinning, and NC State gives 2 to 3 inches. If you plan to harvest whole plants, the Illinois guide says closer spacing without thinning is satisfactory. Pick the figure that suits how you will harvest, and write it down.
Why did my spinach go to seed so quickly?
The likely cause is heat and day length. The Wisconsin guide says the plant bolts “under warm temperatures and long day length,” and the Illinois guide says it bolts quickly during the long days of late spring or summer. Slow-bolting varieties and a planting date in early spring give the crop the best chance of a long harvest.
Are the thinnings edible?
Yes. The Illinois guide says late thinnings may be harvested as whole plants and eaten, and the Wisconsin guide suggests the tender leaves of thinnings for salad greens.
Bottom line
Sow spinach shallow, in cool weather, and thin the seedlings to a spacing that matches how you plan to harvest. Choose slow-bolting varieties for spring, and plan later sowings around the heat the sources warn about.
Sources
- https://extension.illinois.edu/gardening/spinach (opened 2026-10-23)
- https://plants.ces.ncsu.edu/plants/spinacia-oleracea/ (opened 2026-10-23)
- https://hort.extension.wisc.edu/articles/spinach-spinacia-oleracea/ (opened 2026-10-23)
- https://extension.umd.edu/resource/starting-seeds-indoors (opened 2026-10-23)
- https://extension.usu.edu/yardandgarden/research/starting-vegetable-seeds-indoors-germination (opened 2026-10-23)
- https://extension.unh.edu/resource/starting-plants-seed-fact-sheet (opened 2026-10-23)
