When to plant onion sets if you want delicious onions on tap

Not sure when to plant onion sets? We've got you covered with our expert guide

A trough of onions and sweetcorn in a vegetable garden
(Image credit: Getty Images)

If you want to know when to plant onion sets in your vegetable garden, you've come to the right place. 

Our team of experts at Ideal Home are big fans of the GYO garden trend, and know all too well that the 'when' is every bit as important as the 'how' when it comes to growing your own onions.

With that in mind, then, we've worked with some horticulturalists and pooled our knowledge to bring you a definitive guide on when to plant onion sets. You are very welcome! 

When to plant onion sets

Before we start talking about when to plant onion sets, let's spend a little time talking about... well, about what onion sets actually are.

'Onions are usually grown from sets, and these are immature onion bulbs that start growing again shortly after they are planted,' explains Morris Hankinson, founder of Hopes Grove Nurseries

Morris Hankinson of Hopes Grove Nurseries
Morris Hankinson

Morris Hankinson is the founder and managing director of Hopes Grove Nurseries Ltd, the UK’s only specialist grower-retailer of hedging plants, which he established after graduating with a Commercial Horticulture Degree from Writtle College, Essex in 1992.

Onion sets, Morris goes on to explain, are 'the easiest and fastest way to grow a crop with more predictable success compared to growing them from seeds, which despite being cheaper need more care and attention, particularly in the early stages'. 

Where to buy onion sets:

So, when should onion sets be planted? It all depends on when you want to harvest them...

Autumn-planting onion sets

We've spoken a lot about the best fruit and vegetables to sow in November, and you'll be pleased to know that onion sets well and truly fit into this category.

Onions in the soil of a vegetable garden

(Image credit: Getty Images)

'Autumn planting onion sets will yield an early crop that is ready for harvest in June and July,' says Morris.

'They should be planted in autumn while the soil is still warm for successful establishment, ideally from late September until early November.'

Spring-planting onion sets

If you want to know when to plant onion sets in the springtime, Christopher O'Donoghue, one of the co-directors of Gardens Revived, advises that you plant them when the soil is warm and dry.

Christopher O'Donoghue, one of the directors of Gardens Revived
Christopher O'Donoghue

A gardener with over a decade of experience under his belt, Christopher set up Gardens Revived with his brother, Andrew, in 2018  to create a thriving family business. Together, they have worked on residential gardens, listed buildings and gardens, flower shows and large estates with some exceeding 70 acres – many with historical significance.

'You're aiming to get them in the soil sometime between March and April,' explains Christopher, adding that they should be ready to harvest from late July or August.


What month do you plant onion sets?

If you are trying to determine when to plant onion sets, it's important to consider when you're hoping to harvest them.

If you want to tuck into your onions from June and July, you'll want to sow them sometime between late September and early November. If you're happy with late-summer onions, you can plant them between March and April.

The Royal Horticultural Society (RHS) adds that you 'can sow onions outdoors from late winter until mid-spring, once your soil is drying out and beginning to warm up'. 

Can you grow onion sets in pots?

Are onion sets frost hardy?

Onions are pretty hardy, so try not to worry too much about them: they should be fine in light and moderate frosts. If your garden undergoes a hard freeze, though, there's a chance of damage. 

Keep an eye on the forecast and cover them in a protective garden fleece from Amazon if the temperature looks like it's going to dip below freezing.

Can you plant onions in December?

'Onion and leek seeds are traditionally planted on Boxing Day for the earliest crops and largest prize-winning specimens,' says Morris. 

'Start them off in pots or multi cell trays in the greenhouse planting 2-3 seeds in each and thinning them out to leave the strongest plant as they develop. Plant them outside in well prepared soil in spring.'

Now that you know when to plant onion sets, all that's left to do is get out in your garden and start sowing.

It'll be worth it for that first bowl of homemade (and homegrown) French onion soup, trust us!

Kayleigh Dray
Acting Content Editor

Kayleigh Dray became Ideal Home’s Acting Content Editor in the spring of 2023, and is very excited to get to work. She joins the team after a decade-long career working as a journalist and editor across a number of leading lifestyle brands, both in-house and as a freelancer.