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Best expert advice on growing onions

Shallot 'Meloine' from Suttons

Sowing onion seeds or growing your own from onion sets is relatively easy and incredibly satisfying. Here, we’ve brought together the best onion-growing content from the internet, including articles, videos and instagram posts to help you plant, care for and harvest onions at home. Whether you want to cultivate brown, red, salad, pickling or exhibition-sized onions, here are some expert tips to ensure you succeed. 


Best advice on growing onions from sets

Onion sets ‘F1 Centurion’ from Suttons in a basket
Growing from sets is an easy way to get a crop of pungent, flavoursome onions
Image: Onion sets ‘F1 Centurion’ from Suttons

Novice gardeners can learn a great deal about growing onions from sets from the very informative article Know your onions! #DigYourOwnAForCorona by the ever wise and witty sisters also known as The 3 Growbags. They say onion sets don’t like a fuss and prefer soil without manure. You should plant them with their “little papery noses” just sticking out of the soil, and initially throw a net over them to deter pecking birds looking for nest material. 

David Domoney declares that growing onions from sets is an easy project for the beginner veg gardener. In his thorough blog post on onion growing he suggests popping them in an open, sunny site, but adds that you can also grow onions from sets in containers. Make sure to keep them well watered in hot weather, though, or they may bolt – producing shoots and flowers rather than good size bulbs. 

In the north of England, Dan from Allotment Diary is a man who really knows his onions – he’s grown a 10lb-er for exhibition before. In his short, but sweet video Growing Onions: How to get an early start with sets, he shows how he starts off his onion sets in 24-cell trays. Because of the cooler climate where he lives, he grows them on in the greenhouse or polytunnel so they have good strong roots and the soil outside has time to warm up before he plants them out.

Most of the hard work has been done for you when you grow onions from sets and it’s easy to get a fantastic crop, according to Tony at Garden of Eaden. In his detailed article on growing onions he explains how to establish a permanent onion bed – on a sunny site with good drainage – that you maintain well to build up soil fertility and eliminate diseases.

If you want a simple and quick how-to guide for growing onions from sets, then Scotland’s The Pink Wheelbarrow, aka MT O’Donnell, has it well covered, especially if you live in colder climes. Gather all the elements you need – modular seed tray, general multi-purpose compost and onion sets – and you can get your onion crop started off in 10 minutes. Four to six weeks later they’ll be ready to plant out.

Most people plant their onion sets in early spring for late summer harvesting, but in her informative article: Onions: seed or set? Mandy at Mandy Can U Dig It reminds us that you can also plant them in autumn and they can stay in the ground through the winter for an earlier crop around June or July.

Best advice on growing onions from seeds

Onion seeds ‘Ailsa Craig’ from Suttons
Sow a variety of onion seeds and plant out the strongest seedlings to grow on
Image: Onion seeds ‘Ailsa Craig’ from Suttons

For choice, satisfaction and maximum yield, Steve at Steve’s Seaside Life always starts off his onion crop by sowing a range of seed varieties, as he explains in his great video introducing his onion seedlings. While admitting his results aren’t always as good as he’d like, using seed means he can over-sow, then select the best seedlings to grow on for a mix of onion sizes – some large, lots of medium for storing and enough small ones for pickling. And any spindly spare seedlings can be usefully grown on as salad onions. 

Muddybootz, aka Nigel Jewkes, is another fan of growing onions from seed, for ease, economy and variety. As part of his ‘Growing Made Easy’ series, he provides an excellent step-by-step guide to growing onions, from sowing in quarter seed trays of worm compost and warming them in a propagator, to potting on, planting out and harvesting. 

When it comes to growing onions, the Two Thirsty Gardeners had differing opinions so went head-to-head in an interesting “plant wars” trial. Nick, believing that seed-grown onions are more economical and produce larger, healthier and tastier crops, opted to try growing onions from seed. He compared the progress of his seedlings with the sets planted by his friend Rich and observed that the plants sown from seed developed much more slowly so were likely to be later cropping.

Best advice on planting out onions

Onion sets ‘Red Ray’ from Suttons
Plant alternate red and white onions for an attractive display and delicious crop
Image: Onion sets ‘Red Ray’ from Suttons

Neat straight rows of onions look really attractive in the veg bed, especially if you alternate white and red varieties when you plant them out, according to Carol, aka The Sunday Gardener. In her delightful step-by-step guide to growing onions with complementary video she also points out that onions make great companion plants, deterring carrot fly and slugs from other veg crops planted nearby.

Claire, from Claire’s Allotment, started her onion sets off in cardboard toilet roll tubes in the greenhouse. She shows how she leaves the sets in the tubes when they go in the ground in her concise and easy-to follow video: Planting out my onions. She plants them about 4in apart in a raised bed, explaining that the cardboard will biodegrade, giving the onion bulbs plenty of room to swell up. And she reminds us to weed and water them on a regular basis.

If you have limited space, then it’s possible to grow onions in containers. Plant your onion sets in pots, like Dan of Urban Turnip. He’s a big fan and says there’s nothing like having your own carefully-tended onions hanging up in a shady spot in the kitchen. He explains that although you should aim to plant them 3in apart, planting them closer in a container still works. You’ll just have smaller onions.

A serious allotment grower, Cliff at Castle Hill Garden shares his onion planting techniques in this garden update video from his plot in Nottinghamshire. He grows from seed and plants his onions out – cutting uniform holes with a bulb planter – in a double dug bed that has a deep manure base for the roots to feed on.

Best advice on onion problems, pests and diseases

Exhibition sized onions
Prevent your prize onions from succumbing to common problems
Image: Shutterstock

While onions are usually trouble-free plants, John of Allotment and Gardens – who shares plenty of excellent onion growing tips – flags up a few hazards to watch out for in his eye-opening article: Onion Pests, Diseases & Problems. He explains how to recognise onion fly, white rot, leaf miner, rust, mould and mildew; provides advice on what to do if your plant starts to bolt; and shares practical tips for putting off pesky pigeons. 

If you’ve had problems with onion or shallot bulbs rotting in wet soil, like Hayley at Hayley’s Lottie Haven, you could try her trick of starting sets off in small individual pots of multipurpose compost in the greenhouse. She plants hers out after they’ve developed a really healthy root system.

Onions can be very forgiving, even if you neglect them a little, like Bryony at Linnet Lane who confesses to throwing some sets in the ground and ignoring them. Although she failed in her task of regular weeding, she was delighted that the onions graciously grew anyway. Bryony did have to pay the price of a weed-ridden bed to clear out once the onions were drying, though.

Best advice on harvesting and storing onions

Onion sets ‘Hysky’ from Suttons
Drying your onions well before storage helps them keep longer
Image: Onion sets ‘Hysky’ from Suttons

Knowing when and how to harvest and dry your onions is really important if you want them to store well through winter. Tony of Simplify Gardening charts the process thoroughly in his video guide. He says to choose a bright day without rain to lift your onions after their necks have flopped over, being very careful not to pull and damage them. Then remove the soil from the roots before letting them dry out in the sun.

It’s tempting to whip your onions out of the ground as soon as their stems drop a little, as Sue of Bridge Cottage Way demonstrates in her Instagram image. She believes in biding her time to let more “magic happen” and recommends you wait until the onion stems are really droopy before harvesting.

Where you put your onions while they dry is a matter of choice, and whether you have useful aids or props available. Matt at Grow Like Grandad has tried various methods successfully, including using mesh metal trays and even an old shower door.

Once your onions are dry, you’ll probably want to store some. For a step-by-step guide to stringing onions in a simple braid using baling twine, look no further than the excellent video from Liz at Byther Farm. She chooses onions with a nice strong stem for storage; ones that have a soft neck or a short stem are set aside to use straight away.

Braiding your onions or shallots for winter storage can be hugely satisfying, as illustrated by Katrina of Homegrown Garden in a picture that contrasts her plaited shallot string with her own hair braid. She was particularly pleased with her crop – she says alliums don’t often thrive on her plot for some reason.

If braiding is too much fuss for you, follow Pink Wheelbarrow’s tips on how to harvest onions and store your crop in a hessian bag or an unsealed crate. You can even hang them up in an old pair of tights in a cool, dry spot and they’ll keep well for months.

So, now you know your onions a little better, put some of this great advice from the experts into action and you could be harvesting your own crop this summer, with plenty of onions to keep you going through the rest of the year.

Lead image: Shallots bulbs ‘Meloine’ from Suttons

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