So you want to grow spinach in your fall garden… but it’s mid-summer, the weather is super toasty outside, and spinach seeds are those oddballs in the gardening world that won’t germinate when the soil is too warm. (Say what?!)
Here’s something most people don’t know: Spinach germinates best (and fastest) between 65°F and 75°F. Germination rates decrease as you move toward the higher end of this spectrum—which is why gardeners who sow spinach outside in July or August experience poor, if any, germination.
Related: THE ideal soil temperatures for germination all kinds of vegetable seeds
Spinach is a cool-season crop that fails to germinate in soil temperatures above 75°F (it’s more finicky than even peas and lettuce), but there’s a trick to getting your seeds started when it’s hot outside (and it’s not just sowing more seeds).
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Pre-germinate your spinach seeds
If you want to plant spinach in the summer for a fall harvest, you must first germinate your seeds indoors. My technique makes spinach sprout in three days without any fancy setup!
I usually pre-sprout a few different varieties of spinach to hedge my bets for fall. Some are more frost hardy than others, and some bolt more slowly when planted in the heat of summer. All spinach varieties benefit from the same treatment.
First, start with a soak
Take a small handful of seeds and soak them in water overnight for up to 24 hours. This causes the seeds to absorb water and swell so that they break earlier (thereby releasing their food reserves and triggering embryo development).
Use the paper towel method
The paper towel (or baggie) method is a quick way germinate the seeds on paper towels or coffee filters.
- Take a paper towel or paper coffee filter, wet it and squeeze out the excess water so it doesn’t drip.
- Drain the pre-soaked spinach seeds, spread them over the paper towel/coffee filter and fold in half to squish.
- Place the paper towel/coffee filter in a small resealable bag.
Find a cool place for your seeds to sit
At this point, some continue with the cold moisture layering process and place the bag in the refrigerator to encourage germination.
However. I’ve found that spinach seeds take a few weeks to germinate in the average 37°F refrigerator environment, and I just don’t have the patience for that.
Did you know that?
Spinach takes up to a month to germinate at 40°F but only five days at 75°F. Temperature matters!
Instead, I look for the coldest place in my house that isn’t the fridge or freezer, and that’s usually right above a floor vent as the AC blows cold air. For other people, this might be a basement, a room on the north side of the house, directly under a ceiling fan, or in front of a window that gets a cool breeze throughout the day.
I put a digital thermometer on the stool where I put my bags and the temperature stayed between 68°F and 72°F all day at this point.
Within two days, the first handful of seeds had sprouted and made little white roots.
By the end of the next day, I had more than 50 percent germination in all three spinach varieties. I moved this first batch to the seed starting trays below my lights. (The rest eventually sprouted over the next two days.)
Your seeds won’t germinate all at once, so it’s important not to let them sit in the bag for too long (otherwise they may start to mold).
Once the seed pods have broken, transfer each sprouted seed to moist potting soil and cover lightly with soil. Keep moist and within two to three days, the root will be hooked into the soil and cotyledons will emerge from the seed coat.
Why didn’t I plant them outside?
Like other cool-season crops, spinach struggles in the heat and it’s a challenge to manage the shade and moisture it needs outside at this early stage. Combine it with summer pests such as earwigsflea beetles and aphids, and it becomes even more difficult to raise spinach seedlings outdoors without frying or eating them.
But in the controlled environment of an indoor grow light setup, you can let your spinach grow strong and healthy for the next four to six weeks while the chaos of your summer garden fades away. Then, as the late summer heat begins to wane, the cuttings are hardy enough to move outdoors (after hardening off).
Read more: How to harden off the seedlings before planting them outside
Make your transplants in the garden easier
i like to hang shade cloth over my spinach for the first week or two to acclimate the new transplants. They will become more productive as the weather cools and you may even be able to harvest well into winter (although the plants will stop growing once Persephone’s period arrives).
Spinach is incredibly frost hardy (down to the low 20s Fahrenheit) and many varieties, such as Bloomsdale, Giant Winter and Space, will reliably overwinter. Other varieties, such as Tyee and Winter Bloomsdale, are hardy enough to survive 0°F weather.
Plants usually die after a prolonged hard freeze, but will sprout new leaves in the spring if you keep the bed covered with a medium weight frost cloth. (Just remember not to let the leaves touch the fabric.)
Here are more frost tolerant vegetables you can grow in winter (all without greenhouse).
