How to grow onions and leeks

Onions and leeks are not often grown by home gardeners because they’re so cheap to buy, but with onions being one of the most heavily sprayed crops when grown conventionally, we like to grow our own organically.

Onions and leeks are sown slightly differently from your regular veges.  Firstly, you’ll need a deeper dish than the usual seed sowing container because these veges have a long tap root.  You’ll have to bore some holes in the container if it doesn’t have any. 

Make sure you have fresh seeds and store them in the fridge for a couple of weeks beforehand, then sow them as you normally would, soaking them in a seaweed solution once sown until the medium is nicely damp. We recommend putting a cake rack over the container and draping a wet tea towel over that to create a humid environment to assist germination of the seeds.

See Rob sowing onions and leeks in this video.

These little seedlings were all up after about 5 days.

In about 6 weeks’ time they’ll be big enough to plant out.  Onions grow on mounds and leeks grow in trenches, so you can hill them up (like potatoes) and have nice long white stems.  Add lots of compost to your garden bed so the soil is nice and friable.

With both onions and leeks, we bareroot them, so pop your seedlings into a bucket of water and gently wash off the soil.  Once they are barerooted, trim the tops off and also some of the roots.  This way the plants can focus on getting established. 

Using a dibber, plant onions about 20 cms apart.  Organically-grown onions grow bigger than conventional ones and they shouldn’t touch each other while growing, otherwise they can rot.  You can plant leeks 10 cms apart.  We would recommend adding a general purpose fertiliser like Natures Organic Fertiliser round the plants and water in well.  If your soil is dry, water every second day until the plants start growing.  We would add another dose of fertiliser after about 6 weeks, and also give the plants a liquid seaweed feed every 2 weeks or so to keep them disease-free. 

See Rob planting onions and leeks in this video.

Don’t forget to hill leeks up during the growing season.

One key thing about onions and leeks is that their beds need to be kept weed-free.  They are slow growers – onions planted in autumn can take 6 months to fully mature.  Weeds grow faster and can tend to crowd them out. 

The best companion plant is viola, but it’s too early to plant viola when you’re planting your onions and leeks.  Wait till May to plant it.  Viola doesn’t compete with onions and leeks for nutrients, so it works well.

Onions will be ready for harvest when the tops die down – after at least 6 months.  At that point, gently remove them from the soil (using a fork) and lay them on the garden bed for a few days to fully dry out.  Then they can be hung or laid out in a cool, dark place to be enjoyed for the rest of the year.

Leeks will stay in the soil until you need them, which is nice and convenient of them. 

Good Day Long varieties (grown in early spring for late summer eating – thin-skinned – they don’t store): Yellow Sweet Spanish, White Sweet Spanish, Red Brunswick

Good Day Short varieties (grown in early autumn for late winter eating – thick-skinned – store well):  Pukekohe Longkeeper, Italian Longkeeper, Californian Red


Organic Edible Garden’s vision is to make organic edible gardening achievable for everyone. Visit their website for Getting Started videos, and regular blog posts to find out what to do in your edible garden.