How to Plant and Overwinter Spinach for the Earliest Spring Crop

Spinach is something of a contrary crop. That is to say, it hates heat and won’t germinate in soils over 68℉ (20℃). Then, it bolts and goes to seed at the slightest mention of heat.

You pretty much cannot grow spinach through the warm summer months when most of the garden is going gangbusters.

Jump to:

• A good early and late cold hardy crop
• Like winter Sowing, Minus the Milk Jugs
• How and When to Sow Overwintering Spinach Seeds for Early Spring Harvests
• Mulch well
• Manage the mulch in the spring
• What variety of spinach should you use for overwintering/in-ground winter sowing?
• What if the weather stays warm, and I have some germination?
• Winter Sowing Spinach Seed is Another Way to Extend Your Harvest

A good early and late cold hardy crop

Spinach is a crop to grow early and late. This is nice, because it means it is very cold hardy and is a good alternative to more sensitive crops. You can be growing and harvesting spinach long before many other greens, including hardy lettuces, and long after, too (if you time your plantings right).

One of the best ways to get the earliest possible spinach crop -- before you’re really thinking about actively spring gardening -- is to direct sow spinach in the late fall or winter. Then, it is in the ground before you can work the ground, and it will germinate and grow as soon as conditions allow in the spring.

Like winter Sowing, Minus the Milk Jugs

This method is basically winter sowing. It is a lot like the winter sowing method that has become popular for starting garden seeds and transplants; the one where you sow seeds outside in milk jugs.

The difference is that you’re sowing your seed directly in the ground where you plan for the spinach to grow. And you’re sowing at the end of one season for the beginning of the next.

The plan is not really for this spinach to sprout and grow now. It is for the seed to be in the ground, laying in wait, until it naturally decides to grow. If you’ve ever had spinach, go to seed in your garden to then find it voluntarily sprouted and grew early in the next spring, think along those lines. This is basically the same thing.

There are advantages to direct sowing late spinach seed in the late fall and winter:

• Nets you the earliest possible spring crop and harvest
• Potentially, you’ll have spinach to pick long before the garden season when things are still quite cold (probably before you’re thinking much about gardening)
• Spinach doesn’t care for transplanting and having its roots disturbed, so you may find more success with this method that requires no transplanting
• Less weed competition -- weeds won’t germinate at planting time, and the spinach will beat most weed seeds in the spring. Plus, it will already be mulched against weed invaders.
• No indoor grow lights or electricity are needed for starting transplants indoors
• Over time, if you let the plants set and then save seed, you can select for traits like earliest harvest, cold hardiness, etc.
• Good early harvest option for nutritious homegrown greens
• Start harvesting your own (cheaper!) food earlier
• Use your harvest fresh, like lettuce, or use it for cooking, sauteing, in soups, and more

How and When to Sow Overwintering Spinach Seeds for Early Spring Harvests

The key to success with this planting method is to sow the spinach seed late in the season after the soil has cooled. That way, you are laying seed that will lie dormant, not seed that will germinate and grow now. This seed is meant to sprout and grow in the spring.

Sow late in the fall or winter

Sowing should occur late in the year. The best time is very late in the fall or early winter.

Plant your spinach at about the time when it’s still technically fall, but it feels a lot like winter and most of the world is dead or dormant.

That said, it’s almost never too late to sow spinach for overwintering.

Do it while you can still work the soil (though even partially frozen soil is fine to work in. You only need to be able to scratch down about one-half inch into the soil. As long as you can do that, you can sow the spinach seeds.

Even if the ground has started to freeze, you can still sow spinach to overwinter for early spring growing.

What’s more important than a calendar date is to pay attention to your conditions and sow the spinach seeds after it has gotten adequately cold enough to prevent germination until the spring (more on this in the section below).

Weather and climates are changing. Some years are much warmer than others. Let your local conditions guide you for this year.

Sow when soil is below ideal germination temperatures

Spinach germinates at very low temperatures. It can sprout in the soil as low as 40 to 45℉ (4.4 to 7.2℃), though around 50℉ (10℃) is more common. So, to sow your spring crop, you need to wait until your soil temperatures are consistently in that low range or lower.

>>> Sow overwintering spinach seeds when soil temperatures are between 32 and 45℉ (0 to 7.2℃)

>>> Between 35 and 40℉ (1.6 to 4.4℃) is even better

For many of us, soil temperatures may not even fall that low in fall. It may take until late fall, or even into the early winter for soil temperatures to get that low.

Note that we are looking at soil temperatures here, not ambient or air temperatures. Soil temperatures will generally fall more slowly in the fall than the air temperatures do (because soil temperature stays more stable).

However, after several nights of frost or freezing and cool days, your soil temperature may fall low enough, and then it tends to remain stable at low temperatures, barring unseasonable extended warm ups.

Taking the temperature of your soil is easy, and it doesn’t require anything more than a probe thermometer. Here is how to take an accurate soil temperature reading: How to Take a Soil Temperature Reading

How to sow spinach seeds for overwintering

The actual process of planting the seeds is no different than planting seeds in the spring:

1. Cut a small trench into the soil, one-half inch deep

2. Drop spinach seeds into the trench, spaced every one to two inches

3. Cover the seed with the loose soil, then tamp down

4. Because you do not want the seed to germinate now, you do not need to water. Winter snow and moisture should provide the moisture that is needed for germination by the spring

5. However, if your soil is very dry, or if you have been in drought conditions, you may want to water the soil before you plant. This will make the soil more workable and will keep a low level of moisture in the soil for the seeds.
6. If you need to pre-water, water the day before you plant your spinach seeds, or several hours before planting so the water can disperse into the soil and you are not putting your seed into very wet ground.
7. Proceed with mulching (below)

If the ground has started to freeze and/or cannot be dug into:

1. Sow the spinach seed on top of the frozen ground and then cover it with loose, unfrozen soil, potting or gardening soil, or a layer of compost
2. The layer of soil you lay over the row should be the same as the typical planting depth -- about one-half inch deep
3. Slightly thicker is better than slightly thinner for this type of growing
4. Proceed with mulching (below)

Mulch well

After your seed is planted, mulch it.

For overwintering/winter sowing spinach in the ground, mulching serves two main purposes:

1. Mulch keeps moisture in the ground. It also allows moisture to filter through from winter snow and rain. Dormant seeds do not need a lot of moisture, but they should not completely dry out either, and they will need it after the winter to germinate in the spring.
2. Mulch locks cold into the ground. This will help to keep the seeds dormant during warm snaps so they don’t germinate prematurely and then have the tiny sprouts die off. A good mulch layer will also block the sun from warming that top layer of soil with its direct heat.

Good mulch materials for spinach are straw, sawdust, or chopped leaf litter.

To get more protective cold into the ground, you may even wait to mulch until the ground freezes (or comes as close to it as it is likely to get). A layer of three or four inches of mulch will hold the temperature of the soil stable for longer.

More stability in soil temperature -- even frozen, cold stability -- helps to prevent seeds from heaving up and being displaced out of the ground and soil.

Manage the mulch in the spring

In the spring, pull back the layer of mulch when things start to thaw.

Let the soil where you planted the spinach warm up, then re-cover it with a thinner layer of mulch (one to two inches thick so the spinach can come up through it but you still get protection from weeds).

A few days of exposure to air temperatures and the sun should be enough to let the soil thaw and warm up for the spinach to begin growing. If you’re not sure when to do this, about the time the garlic starts to sprout is a good time.

If you don’t grow garlic, do it as the spring thaw begins, when the top of the ground starts to thaw and get a bit muddy. But do keep an eye out -- this is often sooner than you think! And the sooner your ground warms, the sooner your spinach can grow and feed you!

What variety of spinach should you use for overwintering/in-ground winter sowing?

You can do this with basically any variety of spinach.

• Cold hardy varieties like Acadia will offer more resistance to cold damage, but this is not much of an issue for cold-loving spinach.
• Acadia is also a fast growing variety that can be picked in as few as 27 days, so that will also help to speed up your early harvest come spring.
• If you find that your cold hardy variety is a little too hardy and sprouts prematurely, you may opt for a variety that germinates at higher temperatures (though around 50 to 60 ℉ or 10 to 15℃ is about the upper limit of spinach germination soil temperatures).

What if the weather stays warm, and I have some germination?

Climates are changing. For many of us, the weather is staying warmer for longer. This is all evidenced by the fact that the USDA had to reconfigure their hardiness zones last year, and many growers found themselves in warmer, changing climates (with implications for longer, warmer growing and lower winter hardiness).

Because spinach is cold hardy, and can germinate at low temperatures, there is a chance that it will sprout and grow if your seasons don’t stay in their lane.

If this happens, it’s not worth fretting over. There are a few things you can do:

• Enjoy the late harvest. Lucky you -- you’re growing spinach for fresh harvesting in the winter! Spinach growing in cold weather is often richer and sweeter in flavor.
• Harvest if it gets to a large enough size to be worthwhile (baby leaf or larger).
• Mulch the plants, mounding up around them, and they may surprise you and over winter even after the temperatures fall back down. If they live they will grow new leaves for harvesting when the spring arrives for real.
• If you’re concerned you won’t get that early spring crop like you were planning when the temperatures drop and seem more steadily cold, sow another round of seed.
• If the ground is too hard for planting, use the “frozen ground” method outlined above.

Winter Sowing Spinach Seed is Another Way to Extend Your Harvest

There’s a lot to be said for late planting methods like winter sowing spinach to overwinter for early spring harvest. This is a way to extend your harvest without having to go to extraneous measures. You’re simply extending it on the early side, but without having to cover and baby the crop!

Another benefit is that you can do the planting at a time of year when there aren’t a lot of other gardening tasks to be done. That means less competition for your time, and more growing.

Simple season extension methods like this mean more easy growing and good food you grow yourself without adding stress and workload to the point of imbalance. Happy growing, and enjoy that early spinach next spring!