Ready to start your own onions from seed? Below you'll find a step-by-step, numbered guide outlining exactly how to do just that. There are lots of ways to garden, this is just what works for us. Do comment if you have any tips to add or share!
WHEN TO START ONION SEEDS
Why start onion seeds in January or February? It's because they take a LONG time to mature and in the north, we have a shorter growing season.
One of my chosen varieties this year, Redwing, has a maturity date of 110 days! As with many seeds, that’s days from when the *seedling* is transplanted to the garden, not from when the seed itself is started indoors to get you that seedling. You need to add another 8-10 weeks for the onion seed to germinate and grow indoors before it’s a good size seedling (pencil-thick) to transplant outside.
SELECTING "LONG-DAY" VARIETIES
In Canada and the northern US, we want to select “long-day” varieties. They are going to grow until there’s 14-16 hours of light per day (May-June in southern B.C.) and then start to bulb. Each leaf of the onion plant is one ring of the onion, so more developed plants, with more leaves, will have larger bulbs.
You won’t need a lot of space to start onion seeds indoors (one variety per container is fine), but I do recommend having a grow light.
In my experience, gardeners have better success with seeds than sets. Onion sets are baby onions, stopped part way through growing, which results in them being more stressed and having a higher tendency to bolt (stop growing larger and instead begin flowering). That said, sets are very easy to plant and don’t need to be started early, so don't feel guilty if you go that route.
SOWING INSTRUCTIONS
1. Choose your container and ensure it has drainage holes.
2. Fill it with pre-dampened seed starting mix. (I’ll refer to this as soil going forward, but I do mean seed starting mix, not fresh soil from the garden). Fill it all the way up because the soil will compact some as it’s watered over the next few months.
3. Sprinkle your onion seeds on the surface. Unlike many seeds, they can be planted quite close together and then separated much later.
4. Sprinkle another 0.5-1 cm of soil on top and gently pat it down, securing the seeds in place.
5. Wet the surface by misting it, instead of running a stream of water, which could move the seeds. It should be very damp but not soggy.
6. I recommend sprinkling cinnamon on the soil surface to protect against fungal diseases, like damping off, which thrives in a wet environment and can kill seedlings.
7. Cover the container to keep the humidity up. One easy option is to use a clamshell container as your mini humidity dome.
8. Put it somewhere warm, around 20-25°C. They will germinate faster if on a heat mat or warm surface. Expect them to take 1-2 weeks to germinate.
9. As soon as you see that the majority of the seeds have started to germinate, remove the lid and move them under grow lights.
10. As each one grows, the seed covering may stay attached to the top of the first leaf. Don’t hesitate to trim those off with scissors.
11. Once the leaves get 4-5 inches tall, they’ll start to fall over from their own weight. Trim them down an inch or two when that happens - give the whole container a haircut at the same time. Repeat that process as needed until they are sturdy enough to easily grow above that height. Better stocky than lanky.
12. Water as needed. One option is to water from below to keep the soil surface drier.
13. Fertilize with diluted fish fertilizer every few waterings.
14. The seedlings will be strengthened by movement, so put a fan on or run your fingers back and forth over the tops. Do this often (daily or more) for the strongest seedlings, but any amount helps.
15. Divide and transplant them to the garden 2-4 weeks after the last average frost date. Here, that will be around April… but more on that soon!
Best of luck getting your seeds started!
- Mariah Wilde, West Coast Plants