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Growing Leeks & Onions From Seed

There are so many benefits to starting your own onions and leeks from seed instead of planting sets or transplants. The most compelling has to be the pleasure and magic of starting your garden in the depths of winter, the smell of potting soil, tiny green things sprouting, and absorbing the vibrant energy of seeds!

Some of the other practical benefits? It’s more economical to grow onions and leek from seeds (with 200 onion seeds and 75 leek seeds per $3 packet); you have a choice of far more interesting varieties; and you’ll have more control over the quality and results.

Leek and Onions seedlings are also easy to manage because don’t take up much space - you can grow hundreds of them in a single seed tray and you don’t have to pot them up!


When to start leek and onion seeds indoors

Most people start seeds for their garden in March or April, but because leeks and onions are slow to grow, you need to plant them around the end of February. Direct seeding into the open garden isn’t really an option for Northern Growers - but by giving them a jump start indoors, you’ll extend your growing season and get huge leeks and onions.

It's important to get the planting date right so that onions will bulb at the right time. Start them at least 10-12  weeks before your last frost date. Find your first and last frost dates here.


Tips for starting seeds indoors

The process of starting onions and leeks indoors is not much different than with other seeds - it just has to happen a bit earlier. Fill your trays with fresh, quality potting soil to about half, then tamp down the soil a bit. Sow seeds on the surface - about 3-5 per cell, then cover with looser potting soil.

Alternatively, you can simply repurpose an old container! Make sure you poke plenty of holes in the bottom to allow for proper drainage.

Your seed trays don’t necessarily need a heat mat, though you can use one if you wish (we never do) - just place the tray somewhere warm, like on top of your fridge or in a window, where the temperature will be consistent.

Keep your soil evenly moist, but not damp, by watering or misting regularly. To retain humidity for best germination rates, cover with a clear dome lid or a plastic bag until they sprout, then remove the cover. If you’re getting algae on the soil then it is too moist, and you risk rotting the  seeds.

If using lights, place the tray under lights once the seeds have sprouted. Gradually raise the lights as the plants grow. You can trim the leek and onion seedlings by an inch or two once they reach about 5” tall to encourage thicker, stronger growth - and use the zesty trimmings to garnish your soup or salad!



When to transplant leeks and onions

By the time you’re ready to plant outside, you’ll have hundreds of healthy little leek and onion transplants ready to go. You don’t even have to pot them up - they go straight from their seed trays into to the garden.

You will have to harden them off, which means moving the trays outside for a while every day for about two weeks before you transplant them. After the last hard frost, you can move them into the garden. Leeks should be planted individually, but most onions can be planted in clumps of 2-4 without reducing yields.


The best varieties for your growing region

Our favourite thing about growing from seed  is choosing from so many interesting and beautiful varieties. It opens up a whole new world of diversity - shapes, flavours, sizes, colours, and more!

As with all seeds and plants, it's important to select onion and leek varieties that are adapted to your growing climate. Onions are sensitive to day-length, which means they need a certain amount of daylight hours to form bulbs.

Long day onion varieties form bulbs when day length reaches 14-16 hours. They are ideal for Northern growers. One of our favourite varieties is Borrettana Cipollini Onion, a sweet, mild onion with a lovely flattened shape.

Two leek varieties we love (aren’t leeks so beautiful?) that grow very well in Canadian climates are Bulgarian Giant Leek, a culinary star, and Carentan Leek, which is an heirloom Swiss leek variety that matures in just 100 days.




Have you grown leeks and onions from seed before? Are you trying for the first time this year? Let us know if you have any tips or questions in the comments below. Happy growing!