Planting Onion Sets and Shallots: Everything You Need for a Bumper Crop

Right. Onion sets. If you want one of the easiest, most satisfying crops you can grow, this is it. You literally push a little bulb into the soil, wait a few months, and pull out a proper onion. It’s like magic, except it’s not — it’s just how onions work. And shallots are even better because you plant one and get a whole cluster back. It’s like a buy-one-get-six-free deal from nature.

Now, I’ve had a bit of a journey with onions, mind you. Onion white rot was the bane of me life for a couple of years. I was growing lovely looking plants and then pulling them up to find this manky white fungus all over the base. Devastating. But I’ve learned a few tricks since then, and I’m going to share them with you so you don’t have to go through the same heartache.

Sets vs Seeds — What’s the Difference?

So you can grow onions from seed or from sets. Seeds are cheaper but they take ages — you’re starting them in January or February, pricking them out, growing them on, and it’s months before they go in the ground. Sets skip all that. You buy a bag of little bulbs, push them in from about March, and you’re laughing.

I use sets. I’ve tried seeds and honestly, I just can’t be bothered with the faff. Sets work, they’re reliable, and you get decent-sized onions without all the nursery maid stuff. Mind you, if you want fancy varieties, seeds give you more options. But for your standard cooking onion? Sets every time.

For shallots, it’s the same deal. Buy a bag of sets, plant them, and each one splits into a bunch of five or six shallots. Brilliant value. I love shallots in cooking — they’re sweeter and more delicate than onions. Gorgeous roasted whole with a Sunday dinner.

When to Plant

Spring sets go in from about mid-March to mid-April. The soil needs to have warmed up a bit — if it’s still frozen or waterlogged, wait. There’s no rush. Like I always say, plant later, sow less. You’re better off waiting for decent conditions than shoving them in too early and watching them rot.

Now here’s something I’ve been experimenting with — autumn-planted onion sets. Japanese varieties that go in around October and overwinter in the ground. You get an earlier harvest the following summer, and I’m starting to think the timing helps avoid white rot. Ronny down the bottom of our allotment swears by it. He plants early, keeps them in pots until about May, and his onions are absolutely massive. Big bloody things. Not a hint of rot. He reckons it’s a timing thing, and I’m beginning to agree with him.

How to Plant Them

Dead simple. Make a shallow hole with your finger or a dibber — about twice the depth of the set. Pop the set in, pointy end up, and push it down so just the tip is poking out of the soil. Space them about 10cm apart in rows about 25cm apart. That’s it. Nothing to it.

One thing — birds love pulling sets out of the ground. Don’t ask me why. Maybe they think they’re worms, maybe they’re just being annoying. Either way, you’ll come back the next day and half your sets will be sitting on the surface looking confused. The fix is simple — trim the wispy tail off the top of each set before planting. It’s that papery bit at the top that the birds grab onto. No tail, nothing to pull. Problem solved.

For shallots, same method but give them a bit more room — about 15cm apart, because remember, each one’s going to turn into a cluster. They need space to fatten up.

The White Rot Problem

Right, I need to talk about this because it’s the number one issue with alliums — that’s onions, garlic, shallots, leeks. White rot is a soil-borne fungus that attacks the roots and base of the plant. You’ll know you’ve got it when you pull up an onion and there’s white fluffy mould on the bottom. The leaves go yellow early and the whole thing just collapses.

The bad news is it stays in the soil for decades. Once you’ve got it, you’ve got it. The only real answer is crop rotation — don’t plant alliums in the same bed more than once every three or four years. I’m lucky with the new garden at the allotment because it’s never been used for growing, so there’s a good chance it’s clean. But me old beds? I’m more careful now.

I’m also starting to think timing plays a huge role. Planting earlier or later than the fungus expects might dodge it. That’s Ronny’s theory anyway, and his results speak for themselves.

Growing On and Harvesting

Once they’re in, onions are pretty low maintenance. Keep them weeded — they don’t like competition — and water in dry spells. Don’t overwater though. They’re not heavy drinkers. A good soak once a week in dry weather is plenty.

You’ll know they’re ready when the foliage starts to yellow and flop over. Don’t be tempted to bend the tops over yourself — that’s an old wives’ tale and it can actually introduce disease. Just let them do their thing naturally.

Once the tops have died back, lift them with a fork and lay them out to dry. If you’ve got sunny weather, leave them on the soil surface for a week or so. If it’s typically British and chucking it down, bring them inside or into a greenhouse. They need to cure properly — the outer skins should be papery and dry. Then you can plait them, hang them in nets, or just store them in a cool, dry spot. They’ll keep for months.

Shallot Secrets

Shallots are genuinely one of the easiest and most rewarding things you can grow. Plant one, get half a dozen back. Can’t complain about that return on investment. They’re a bit sweeter than onions, caramelise beautifully, and they store even longer.

Harvest them the same way — wait for the foliage to die back, then lift gently. Split the clusters apart and lay them out to dry individually. I’ve had shallots last from August right through to March the following year when stored properly. That’s basically free onions for eight months. Cheap as chips. Well, cheaper than chips actually.

Look after yourselves. Take good care. 🌱