Beautiful, golden onions – they’re enough to make you cry! If you really want to know your onions, here come some top tips for growing fuss-free bulbs every time.
Ideal Onion Growing Conditions
The first tip is to give onions exactly what they need: a sunny spot in moist but well-draining, fertile soil. Add compost or well-rotted manure to the soil several weeks before planting, ideally the winter before planting so it isn’t too fresh. You can then add a general-purpose organic fertiliser at planting time to give plants an extra boost.
Heavy clay soils aren’t ideal, but growing onions in raised beds should help the soil to drain a bit better, sidestepping the sorts of overly wet conditions that could cause plants to rot.
Seeds vs Sets
Onions can be planted as ‘sets’, using bought bunches of young plants or starts, or planted as seedlings you’ve grown yourself. I like to start my onions from seed sown in late winter, sowing into pots filled with all-purpose potting mix. After germinating indoors, the seedlings are separated out and transferred into plug trays to grow on for planting in spring.
Sets are basically part-formed bulbs that will give you a bit of a head start. Early autumn is the perfect time for planting overwintering or short-day varieties. Autumn-planted onions mature several weeks ahead of spring-planted onions, so while they don’t store as well, they will provide some very handy early bulbs – ideal for anyone wanting to be as self-sufficient in bulbs as possible.
Give Your Onions Some Space
Whatever you’re planting, proper spacing is really important because it has a direct impact on the final size of your bulbs. Row spacings of about a foot (30cm) apart leaves plenty of room to get a hoe in there among the plants. A decision then has to be made on whether you want normal-sized bulbs, or fewer, bigger bulbs. Personally, I prefer to go for everyday-sized bulbs, and more of them, which means spacing my onions around 4in (10cm) apart, but if its real whoppers you’re after, space them 8in (20cm) or more apart.
Keep on Top of Weeds
Onions have long, thin leaves that don’t shade the soil, which creates ideal conditions for weeds to thrive. Turn your back for too long and weeds can quickly gain the upper hand, competing for resources and compromising your chances of well-formed bulbs.
Regular weeding is essential to keep on top of things. Use a hoe to carefully weed between rows earlier on in the season, while plants are still young, then hand weed once this gets tricky, or to hoik out weeds sprouting within the row. Regular weeding will also reduce the weed seed bank in your soil, giving cleaner conditions for the crops that follow.
Bolting is when plants send up a flower stalk prematurely. It’s a common problem and in the case of onions leads to split or poorly formed bulbs that won’t store for long at all. Two reasons behind bolting are a cold snap soon after planting, and hot, dry weather.
Onions usually flower in their second year, but a prolonged spell of frosty weather in the weeks following planting can trick plants into thinking winter’s already arrived, so that when the weather warms up again, they’re primed to flower. Spring-planted onion sets are at a greater risk of bolting as they are already one season old. So, avoid planting sets too early in spring when hard frosts are still likely, keep them covered if it does turn cold, or start your onions off from seed.
Hot, dry summers can also cause bolting. The solution is, of course, to water, which should also help keep plants cooler in hot weather, while supplying more moisture to swell those bulbs. If, despite your best efforts, plants do bolt, cut off the flower stalk and use the onions as soon as possible.
Harvest and Cure
Your cue to harvest is when the leaves start to turn yellow and flop over from the neck where the leaves meet the bulb.
All onions must be thoroughly dried, or cured, before storing. It’s an important step that helps them develop their protective outer skin, so they keep for longer. In fine weather you can just leave lifted bulbs on the soil surface to dry out, but if there’s damp conditions forecast it’s safer to bring them under cover. Lay bulbs out somewhere with good air circulation – racks are ideal for this purpose – or you could hang them upside down from staging. They should take around two weeks to dry. Store them in a cool, dry place in boxes, nets or woven into an onion string.