Front Range gardeners still have a few months until their warm-season seedlings find homes outdoors. With limited indoor growing space, starting seeds earlier than necessary creates havoc for me as the seedlings vie for top billing under our banks of T5 grow lights.
But with a few years of Colorado garden planning in my toolbox, I’ve learned to organize the indoor seed-starting and direct-sow calendar to maximize the amount of food I’ll be able to produce each year in our small lot. (If you’ve followed along over the years, you know that typically I start the first batch of seeds, chilis, and eggplant in mid-March because they need more time to get established as seedlings before weathering our climate. Then I build out my seed starting plan from there.) This year I’m branching out, or rooting down, with an onion indoor seed-starting experiment and hope to nestle the small bulbs into nooks in our flower beds to save space in dedicated food garden beds.
While I’m well-versed in seed starting after many years of practice, I checked out a few YouTube tutorials specific to onion growing to fill in learning gaps and find out if the YouTube algorithm from that choice would trigger videos from alt-Right onion gardeners dropping conspiracies while fertilizing their aromatic alliums. (So far, YouTube has only suggested innocuous-seeming gardeners in diffusely lit greenhouses and a video on how to make the best Beef Wellington. I’ll keep you posted.)
After taking notes on onion-growing best practices, I pulled out my pack of unopened Baker Creek heirloom Wethersfield Red Onion seeds we purchased in 2020 when the world was unravelling. The package instructions recommend giving these babies two to three months to grow indoors before transplanting, so I needed to get in gear this weekend if I plan to move them to the yard in late April, the latest, ideal onion planting time for our area’s Zone 5b. And for those who garden in northern latitudes with extended hours of sunlight during the summer, be sure to select long-day onion varieties like the Wethersfield Red or Walla Walla to ensure they receive enough light to thrive.
Heirloom seeds like the Wethersfield Red not only offer unique flavors that get bred out of seeds intended for large-scale distribution; these one-of-a-kind varieties usually bring history and a good story. The Wethersfield Red is no exception. This onion variety hails from Wethersfield, Connecticut, a small town built near the Connecticut River during the 17th century.
Founded by a roustabout who’d been shooed away from a neighboring Puritan community, the town of Wethersfield proved its entrepreneurial spirit for a time when it became internationally known for its aromatic red onions. These pungent bulbs were so delicious that those who farmed them often used the harvest as currency to buy goods. That’s a story worth savoring!
All this talk of eye-watering alliums getting you excited to grow your own?
Here's What You’ll Need to Start Onions From Seed
Containers: Grab small pots or a seed-starting setup like this with growing cells, tray to hold the cells with seeds and catch excess water, and a humidity dome. I also love a seed starting set up that includes a capillary mat to draw water up to the seed pots/growing cells
Seed starting mix: I would love to find a mix that does not use peat moss because there’s no way peat is sustainably harvested, but I have not had luck finding a mix and am usually short on time for seed starting. Here's what I've been using the past two years with good results.
Vermiculite: Because these seedlings will stay in these cells longer than I normally allow, this year I’m adding a thin layer of vermiculite to the top of my seed-starting cells to reduce the fungus that tends to grow along the soil surface because of this higher humidity in the grow room.
Large Bowl: I add the seed-starting mix to the bowl and gradually add water, mixing until the soil is moist without being soggy.
Unlike other plants started from seed indoors, you’ll want to add several onion seeds to each cell/pot. Onion sprouts will grow well in a clump, and then when it’s time to transplant, you can remove them from the pot and gently separate the roots and plant so many more onions. Onion seeds also don’t germinate as well after their first year, so I over-seeded to increase my chance of sprouting success.
Seed-Sowing Steps
Sow seeds about ¼-inch deep in moistened soil. and gently cover with a dusting of seed starting mix and then a thin layer of vermiculite.
Mist the growing cells, and place on risers on top of the moistened capillary mat in the tray.
Add about an inch of water to the tray, and cover with plastic wrap or a humidity dome.
From what I've read, we do not need a dedicated light source during the initial germination phase, so I’ve placed these in our house’s back addition where they’ll stay warm and hydrated until I see little green sprouts pop from the growing medium. Then I’ll truck them downstairs to our basement to grow uninterrupted under grow lights on a 16-hour timer until they are ready for transplant. I've also read that indoor onion starts will get leggy before they are ready for the great outdoors. If this happens, grab sharp scissors and trim to three inches above soil level, and then treat those trimmings like chives and chow down! With a late April transplant timeline for Denver-metro gardeners, you still have time to get onion seeds started indoors. If you want homegrown onions but aren’t ready to attempt seeds, check your garden stores this spring for onion transplants or onion sets (packages of small, individual bulbs like these) to bring the allium party to your kitchen.
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