How to grow onions from seed: easy and fun indoor gardening for all the family

Learn how to grow onions from seed indoors – it's easy and can be a fun activity to do with the kids

how to grow onions from seed
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Learn how to grow onions from seed and enjoy a good harvest of this essential cooking vegetables. Growing onions is also a fun thing to do if you've got (bored) children in the house, as it's relatively easy and doesn't require any special gardening skills. 

We do recommend getting young, first-year onion seeds as they give the best results.

Find more food tips and recipes at our hub page. 

How to grow onions from seeds

Growing onions will require a seedling tray, good-quality peat-free seedling compost, and something to replant them into – either larger pots and compost, or a patch in your garden if you have one. 

1. Begin by filling your seedling tray with the compost up to about two-thirds of each compartment. Then, carefully plant the seeds about one centimetre apart. 

2. Lightly cover the seeds with compost and soak the tray in water – you can do this in the sink. What you want is for the soil to absorb as much water as possible, but avoid submerging the tray in water.

3. Line the bottom with a plastic bag and place the tray in the brightest spot you can find, such as a bright window sill. Growing lamps help but aren't necessary. It also helps if the bottom of the tray is kept warm, for example by placing it on top of the fridge. Again, this will help the seeds germinate quicker but isn't essential. 

4. Water the tray regularly with a watering can and diffuser attachment. You should see germination after about a week to ten days. If the seedlings are growing in loops, gently snip them in half to allow them to grow.

5. When the seedling are taller and have three shoots each, you can replant them where you will be harvesting your onions. The should now be grown outside, provided there are no frosts. They should be ready to harvest in five months.