Onions must be one of the most useful vegetables in the kitchen, so it’s definitely worth growing some in your garden if you have space. I know I use them practically every day in one way or another, and homegrown onions are the best.
You can grow onions from seeds or from sets (sets are baby onions), in the spring and in the autumn. Growing from sets is usually easier and quicker.
My straightforward guide below will help you to get started growing onions. And if you want some help with choosing the best onion varieties, have a look at my top picks at the end of this article.
Preparing the Soil
Pick a spot with full sun and dig plenty of peat-free compost into the soil. Onions prefer fertile, well-drained soil with as much sun as you can give them. Keep your patch weed-free, ready for your seedlings or onion sets.
How to Grow Onions from Seed?
You can start sowing onion seed indoors as early as January. This way, you will have seedlings ready to plant out by the time the warmer spring weather arrives.
Sow onion seeds in trays of peat-free compost, each seed about 1cm apart. Once the seedlings are big enough, you can move them into larger pots with fresh compost.
By the spring your seedlings should be a decent size and ready to plant out into the garden. Leave about 10cm of space between each onion plant, and about 30cm between your rows of onions.
Read on for more about how to care for your onions once they are growing in the garden.
How to Grow Onions from Sets?
Onion sets are small onions, bulbs essentially, which you plant straight into the ground either in spring or autumn. This is usually the easiest way to grow onions.
Onion sets are treated to prevent them from bolting. Never heard of bolting? It’s when a plant flowers and goes to seed before you would like it to. When an onion plant bolts, it uses energy to flower instead of developing its bulb, which is not what you want.
Plant your onion sets 10cm apart, just below the surface of the soil. Leave the tips of the bulbs sticking out. Your rows of onions should be about 30cm apart.
Caring for Onions in the Garden
Water when the weather is dry. Remove flowers as soon as you see them. As I said above, you want your onions to put their energy into developing their bulbs, not into producing seeds. Weed by hand around your onions, as the roots are shallow.
Autumn-sown onion sets can benefit from a bit of fertiliser in the spring.
You’ll know your onions are ready to harvest when the leaves turn brown and droop. This means the onions have stopped growing. You can dig them out before this happens though if they are already big enough. Use a fork to gently loosen the soil and lift your onions ready for drying. Read on for more on onion storage.
If you are growing onions in the spring, you will be harvesting them in late summer. You will be able to store and use them throughout the autumn, winter and into spring. Autumn-planted onions will stay in the ground over winter and be ready to harvest the following year in early summer, just when the stored onions are starting to run out.
So by planting onions in both the spring and the autumn, you should have a year-round supply.
Onions will keep for months if they are stored well. Once you have harvested your crop, leave them to dry out on some newspaper. Keep them separated from each other to help with the drying process.
You’ll know they are ready to store when the outer skins are crispy and rustly to touch. Once you’ve got to that stage, you can hang them up in nets and store them in a cool, dark, dry place. Simply use them when you need them.
Growing Onions – How to Deal with Problems?
Birds and Insects Eating Young Onions
Your feathered friends might try to lift your onion sets out of the soil for a tasty snack! Use horticultural fleece to cover your newly planted bulbs. This will give the onions a chance to get established.
Growing onion sets under fleece can also protect your crop from onion fly larvae. Planting parsley around your onions helps to protect from this pest too.
This can be a problem in very wet summers. You’ll notice it as greyish mould on the onions. Planting with plenty of space between sets or seedlings can prevent this. Make sure your onions are thoroughly dry before storing them.
Different Types of Onion
These are the ones you see most often in the shops: big, round onions with a strong flavour. We use them in so many recipes from stews, casseroles and curries to pasta, pies and tarts. You probably also know them as brown onions or cooking onions. Try ‘Sturon’, ‘Setton’ and ‘Bajosta’ – they all keep well, and you should get a good crop. For autumn planting try ‘Radar’.
Red onions are a bit sweeter than yellow onions (although not necessarily milder) and also very versatile. They add vibrancy to any salad. I really like ‘Red Baron’ because it keeps very well, and ‘Robelja’ for its colour and high yields. You can also try ‘Hyred F1’ for a reliable crop. Plant sets in spring.
These are different from the yellow onions we talked about above (although you might think of those big ones you use in cooking as white onions). White onions have white skins, and they are milder and sweeter in flavour. They don’t always keep as well as yellow onions. ‘Snowball’ can be planted in spring or autumn. White onions generally like a dry climate to grow in.
Are Shallots the Same as Onions?
Shallots and onions are different. Shallots grow in clumps a bit like cloves of garlic does. They are not as strongly-flavoured as onions, and are generally sweeter and contain less water. Like onions though, they are easy to grow from sets. You can plant shallot sets in spring – follow my advice above for how to do this, the instructions for onions work just as well for shallots. Try ‘Meloine’ or ‘Longor’ varieties.