How To Grow Onions Step-By-Step

If you have never grown onions before, or perhaps never grown them successfully, then follow along with my guide for onion success this year!

Seeds or Sets

This is the first decision you need to make when deciding to grow onions, do you grow them from seeds or from sets?

Seeds

Seeds are the cheapest way of starting onions, but not the easiest.

Growing onions from seeds is a long process, and ideally, you need an indoor area to start them off in early spring before moving them outside later.

I do grow onions from seed and use the multi-sow method.

This means I sow the seeds into module trays but sow three or four seeds per module rather than growing them individually.

The onions then grow as a cluster when you move them outside. You don’t thin them out; transplant the entire module.

Pros & Cons

Pros

• The cheapest way to grow onions
• Lots of choices when it comes to variety

Cons

• Slow to grow

Sets

Sets are the most popular way of growing onions, in the UK at least.

A set is essentially a small bulb that has been partially grown before being made dormant again.

You then plant the set, which grows into a full-sized onion bulb.

Pros & Cons

Pros

• Easy to grow
• Can be direct planted

Cons

• More expensive than seeds
• Can be more prone to bolting
• Less choice of variety than starting from seed

Planting Seeds

If you decide to sow onions from seed, I highly recommend the multi-sown approach.

Use a module tray or root trainer if you have one, fill it with compost and sow three or few seeds per module.

You want to do this in late winter or early spring, February or March, preferably. You will need to do it undercover in a greenhouse or alternatively indoors.

Planting Sets

Sets are much easier to get going, and you have a much larger window in which to do it.

You can start them in the autumn if you are prepared but worry not if you haven't got them in the ground already as a spring planting is also fine.

You plant the sets so just the tip sticks out above the soil level, give them a good water and then leave them be. Unless we have an unusually dry spring they won't need any additional help.

Ongoing Care

Onions don't require too much ongoing care, one thing you do need to keep on top of is weeding between the rows.

I use an onion hoe for this, as you can see in the photo above. This is just a small handheld row purpose made for weeding between onions. I tested a few different onion hoes out to find the best one here.

Apart from weeding, you want to keep the soil moist during dry spells. Apart from that there isn't much to do, just let them grow and enjoy watching the bulbs swell!

Harvesting

It is fairly easy to see when onions are ready to harvest, the leaves will flop, start turning yellow and generally just look a bit old and tired.

You will also be able to see the onions in the soil, so you will already have a good idea of what size they are.

When you are happy with the size, just pull them up. Grip onto the leaves low down near the bulb and give them a twist and pull, they should lift easily.

Drying & Curing

To dry my onions, I loosely plat them, tie with some string and leave them to hang in my greenhouse for a couple of weeks. They don't look anywhere neat as in the image above though!

Drying is essential as it helps the onions form a tough outer shell that allows them to store for much longer. Make sure the spot you choose to dry them is dry, light and ideally they don't want to be on the ground.

Once the skins have dried you can take them down, give them a light brush to remove the soil and move to their final storage position. I hang mine in my pantry, but a mesh bag is also good.

Eating The Leaves

As my onions are growing I like to snip off some leaves every now and again and eat them.

They taste just like spring onions and can be used in the exact same way. in fact, they taste so similar that I have stopped growing spring onions now to save space for other crops.