There are several reasons I shy away from growing onions: how much space they take up and how small my plot is; how long they need to stay in the ground; and given how inexpensive they are, why bother? But if you’ve started the year with a hankering to begin the growing season, starting onions from seed is a task you can do now.
Many gardeners will be waiting until spring to start off their onions from sets (small, immature bulbs ready for planting), but growing from seed is a less expensive approach, plus there’s a wider range of varieties to choose from. As with any crop started from seed, it is more labour intensive. But if you’re anything like me, you’ll enjoy the challenge.
Onion seeds can be sown in rows in seed trays or multi-sown (3-4 seeds) in a modular tray then placed on a warm windowsill or in a heated propagator, as they need a little warmth to prompt germination. If you’re growing multiple varieties, be diligent with your labelling because all onions look the same at seedling stage. Once their stems appear above ground, wearing their little seed cases for hats, give your seedlings access to as much light as possible. If you don’t have a bright greenhouse or cold frame to house your growing seedlings, you might need to pop them under grow lights until the sunlight is stronger and the days are longer.
Depending on the weather where you are, your onions can be planted into the ground from mid-March onwards. You can prick out your seedlings and plant them out 5-10cm apart, but if you have got multi-sown plants that are doing well, plant them as they are because they’ll grow fine clustered together.
Onions need regular watering, especially during dry spells, but you want to stop watering the bulbs by mid-summer as this can impact how well they’ll store. Also, be careful to avoid watering their leaves because this can encourage the fungal diseases alliums are susceptible to. And keep the ground around your onions clear – they don’t appreciate competition from other plants.
You can harvest onions when they’ve reached a size you’re happy with – this will depend on the variety and how far apart you planted them. For those that can be stored, dry them for a couple of weeks somewhere warm and well ventilated until the foliage is papery, before stashing them in a light, well-ventilated place.
If sowing seeds this early isn’t for you, then you can sow them when spring is closer, alongside their cousins – shallots and spring onions. And, if all sowing attempts fail, you can get your hands on onion sets around then, too.
