So you want to grow spinach in your fall garden… but it’s the middle of summer, the weather is extra toasty outside, and spinach seeds are those oddballs in the gardening world that don’t germinate when the soil is too warm. (Say what?!)
Here’s something most people don’t know: Spinach germinates best (and quickest) between 65°F and 75°F. Germination rates drop as you move toward the higher end of that spectrum—which is why gardeners who sow spinach outside in July or August experience poor germination, if any at all.
Related: The ideal soil temperatures for germinating every kind of vegetable seed
Spinach is a cool-season crop that fails to germinate in soil temps above 75°F (they’re more finicky than even peas and lettuce), but there’s a trick to starting your seeds when it’s hot outside (and it’s not simply sowing more seeds).
Pre-sprout your spinach seeds
If you want to plant spinach in summer for a fall harvest, you need to sprout your seeds indoors first. My technique gets spinach to germinate 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-tolerant than others, and some are slower to bolt when planted in the heat of summer. All varieties of spinach benefit from this 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 makes the seeds absorb water and swell up so they rupture sooner (thus releasing their food stores and triggering the embryo to develop).
(I wrote more about the process of soaking seeds in this post. It works for other stubborn seeds you need to germinate too.)
Use the paper towel method
The paper towel (or baggie) method is a speedy way to germinate seeds in paper towels or coffee filters.
- Take a paper towel or paper coffee filter, wet it, and squeeze out the excess water so it isn’t dripping.
- Strain the presoaked spinach seeds, spread them over the paper towel/coffee filter, and fold in half to sandwich them.
- Place the paper towel/coffee filter in a small resealable baggie.
Find a cool place for your seeds to sit
At this point, some people continue with the cold-moist stratification process and place the baggie inside the fridge to encourage germination.
However. I’ve found that spinach seeds take a few weeks to germinate in the average fridge environment of 37°F, and I simply don’t have the patience for that.
Did you know?
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 inside my home that’s not the fridge or freezer, and that’s usually right above a floor vent as the AC is blowing cold air. For other people, this might be a basement, a room on the north side of the house, directly below a ceiling fan, or in front of a window that gets a cool breeze all day.
I put a digital thermometer on the step stool where I placed my baggies, and the temp stayed between 68°F and 72°F all day in that spot.
Within two days, the first handful of seeds had germinated and grown little white roots.
By the end of the next day, I had more than 50 percent germination across all three varieties of spinach. I moved that first batch into seed starting trays under my grow lights. (The rest eventually sprouted over the next couple days.)
Your seeds won’t germinate all at once, so it’s important not to let them sit in the baggie for too long (otherwise they may start to mold).
Once the seed coats have ruptured, transfer each sprouted seed to damp potting soil and lightly cover with soil. Keep moist and within two to three days, the root will anchor itself in 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 initial stage. Combine that with summer pests like earwigs, flea beetles, and aphids, and it gets even trickier to raise spinach seedlings out in the open without them getting fried or eaten.
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 dies down. Then as the late-summer heat begins to taper off, the transplants are resilient enough to move outdoors (after being hardened off).
Read more: How to harden off seedlings before you plant them outside
Ease your transplants into the garden
I like to hang shade cloth over my spinach for the first week or two to acclimate the new transplants. They’ll get more productive as the weather cools and you might even be able to harvest through winter (though the plants will stop growing once the Persephone Period arrives).
Spinach is incredibly frost-tolerant (down to the low 20s Fahrenheit) and many varieties, like Bloomsdale, Giant Winter, and Space, will reliably overwinter. Other varieties, like Tyee and Winter Bloomsdale, are so hardy they can survive 0°F weather.
The plants usually die back after a prolonged hard freeze, but will sprout new leaves in spring if you keep the bed covered with a medium-weight frost cloth. (Just remember not to let the leaves touch the cloth.)
Where to buy
Here are more frost-hardy vegetables you can grow in winter (all without a greenhouse).
