Growing Onions in Clusters - The Easy Way to Grow from Seed

, written by Benedict Vanheems gb flag

Onion clusters

Received wisdom has many kitchen gardeners starting their onions off from sets – small, immature bulbs that swell to a respectable size within a few short months. But while sets are speedy, convenient and generally reliable, it’s worth noting that onions will also grow handsomely from seeds sown in the dark depths of winter. With all quiet on the vegetable front, it is reassuring to be doing something now that will carry us through to the new growing season that’s just weeks away.

The New Year is a great time to try a new technique, and they don’t get any more efficient than onions raised from seed in module trays. If you’re anything like me then, after taste, the next reason for growing your own vegetables is cost. Home-grown produce can save literally hundreds of dollars, while implementing evermore ingenious ways of driving down the grocery bill is all part of the fun! Onions from seed offer a budget alternative to sets and take minimal extra effort, so why not give them a try?

An Early Start for Onion Seeds

I have often grown onions from seed. It is only forgetfulness on my part that has me turning to sets later on in spring as a means of catching up. You can sow maincrop onions under cover anytime from the turn of the year to the end of February. If spring is later to arrive where you are then sow towards the end of this timeframe (even later in very cold climates) to be sure that the ground will be ready to receive your pungent transplants once they are big enough to go out – you don’t want the soil to be too wet or cold.

Onion seeds

The way to streamline the whole seed-sowing process is to start the onions off in the same module trays from which they will be planted out in spring, thereby doing away with the need for any fiddly pricking out. Use trays with cells that are about 2-3cm (1in) across the top and pack them with quality multipurpose potting soil that’s been sieved to remove any lumps. Make a slight depression in the surface of each cell and drop a modest pinch of seeds - about five to eight - into each. A good tip is to pour the seeds into your hand before sowing – it’s easier and more accurate to count the black seeds against your palm than drop them straight in from the seed packet and hope for the best! A steady hand and a pointed knife to portion out the seeds will ensure an even cell fill.

Once the seeds are in their cells they can be covered back over with a further sift of compost, watered carefully then popped into an unheated propagator to germinate. Don’t worry if you haven’t got a propagator – a sheet of glass laid over the top of the tray will make all the difference. To ensure the darkness necessary for germination cover the glass or propagator with a double-layer of newspaper.

Growing Onions On

Remove the newspaper as soon as the seedlings poke through, followed by the glass/propagator lid when they touch it or the hooked seedlings have unhinged themselves. The seedlings can now be grown on in the greenhouse or cold frame until they are ready for planting out in early to mid spring.

Clump of onion seedlings

One of the joys of starting onions in this way is that there is no need to thin out the resulting seedlings – they can be set out in clusters, exactly as they are. Too crowded surely? Well no, as over time the individual plants will simply push each other apart, elbowing their siblings out of the way to make sure they get the space they need. You won’t get any king-sized bulbs this way but you will get an ample supply of storable, mid-sized bulbs that are perfect for the kitchen.

To give your onions enough room to spread out they will need a little more space than would be typical for planted sets. Rather than the usual 15x30cm (6-12in) spacing, opt instead for a generous 36-40cm (15-16in) apart in each direction. Far from being an extravagant use of space, the cluster arrangement of onions will ensure you get a surprisingly hearty haul from your onion patch. If pests of any description are a problem protect your young plants with a covering of garden fleece until established.

A string of harvested onions drying

The Easy Part of Growing Onions

If you have planted into fertile, firm ground in a sunny spot of the garden then it is pretty much job done from here. You’ll need to whip out any weeds that attempt to compete with your onions but aside from that they should put on girth as fast as the passing year puts on day length. By the end of summer the onions will be ready for lifting and storing following a period of drying.

So what to grow? Many maincrop varieties of onion are available as seed. The most popular that turns up time and again is ‘Kelsae’, a golden onion whose tendency to produce good-sized bulbs serve it well in this relatively crowded, clustered setup. It’s also worth seeking out seeds of ‘Globo’, a newcomer to the scene that’s formed even bigger bulbs in trials. Both are widely available.

By Benedict Vanheems.

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Show Comments


"I've got yellow and blue lupines coming up from seed, have planted about a hundred lettuce, beans, and tomatoes, and would have forgotten my onions if you hadn't mentioned them here! I'm having a terrific time growing indoors, and experimenting with my new cloning machine to see which cuttings root best with the water spray and which root readily in soil. However, I leave my garlic and cilantro in the ground, as they seem to make it through the cold. I trim the tops of garlic all year long. Now if I can just figure out where I put those onion seeds...."
Laura Olney on Saturday 24 December 2011
"Good informative article thank you. However In the UK we always did, successfully grow onions from seed However we have not had much joy here in the Ariege- (SW France) We have an unheated greenhouse which is made of thin poly carbonate We do line with bubble wrap for extra insulation – most things grow well, but onions from Seed? No! Any suggestions . It may help to know we have warmer days than a UK winter but it can drop to minus 8 at night- thankfully not yet this year! "
Peta on Friday 6 January 2012
"I grew onions from seed last year for the first time. It satisfied the "itch" to start growing indoors in anticipation of the outdoor growing season weeks later. My only complaint was the transplantin process. I started the seeds in a flat, and in seperating in what is a rather delicate structure at transplant time, lost a fair number of seedlings to my clumsiness. I am going to try the "plug" technique this year, and look forward to greater success. Thank you for the great information!"
Jenn Rudtke on Saturday 7 January 2012
"Peta, I have been starting many of my seedlings in the kitchen, then transferring them to a small room in my garage where I painted the walls, ceiling, and floor a nice bright color and placed hanging lights over wall to wall benches. An old door rehung keeps the temperature cool, but even, and quite a bit warmer than the outside. I have a seedling heat mat that gently warms the underneath of the most sensitive seeds until they get going, and I have the newest seedlings protected with plastic tops to help hold warmth and moisture. This may help you."
Laura Olney on Saturday 7 January 2012
"Jenn, just a personal tip when I transplant onions or leeks I lift a clump from their initial planting pot/ tray and place them in a jug of water- that way the soil comes away leaving the fine roots untouched or unbroken. of course personally I find the larger they are the better for transplanting- Hope this helps-This growing is an exciting process ! Bon Chance (good Luck) Peta"
Peta on Sunday 8 January 2012
"I think I understand the Plug for startingonion seeds. Is it a little mesh net about the size of a golfball that you place the seeds in? Do you turn the soil in the garden before you plant the plugs or do youjust plant the plug like a bulb?"
Mark Hausammann on Wednesday 11 January 2012
"Again this is just my opinion; the "plugs" I use (when I use them) are trays made up of small "cells”. The sizes of the trays and plugs on the trays can vary from very small, about 3 cm wide and 5 to 6 cm deep to larger ones, about 5/6 cm wide to 6/7cm deep. They were given to me by my brother in law who had a gardeners centre. He used them to grow all his plants from seeds in this type of “try/plug system. They should available in differing sizes from domestic garden. I have to admit they are far easier to use than the “blanket” sowing in trays and it does save the tussle of separating the individual plants. However to me there is something encouraging seeing a mass of plants together in a small tray – call me sentimental….! "
Peta on Wednesday 11 January 2012
"Mark, the plugs are as Peta describes above - a seed tray that is effectively compartmentalised into separate cells. This has the advantage of making life a lot easier when it comes to planting out time. Just poke a cluster of seedlings from its cell, make a hole a similar size to the rootball into prepared ground, and pop the cell in. The seedlings won't even noticed they've been transplanted until they hit all that fresh soil, at which point they should put on a growth spurt."
Benedict Vanheems on Wednesday 11 January 2012
"Mark, there are different sorts of seedling plugs available, and you can buy very inexpensive boxes of refills for each new batch of seeds (re-use the tray). Some plugs are compressed peat, and others are a soil-less medium such as a coir mix. You water them down with warm water, they expand, you plunk in your seeds, you pop the whole thing into a larger size pot or into your garden. The roots can easily penetrate the outside of the plugs, and the plugs will biodegrade in time."
Laura Olney on Thursday 12 January 2012
"This may seem like a silly question, but my husband and I are new at gardening. We planted our first garden earlier last month. We currently have potatoes and strawberries growing, and a few cucumber sprouts have started coming up. However, we are so confused about the onions. How do we know if what is coming up is an onion sprout, or just grass/weeds? I have looked at several pictures of onion sprouts, and they all look similar to grass. I guess what I need to know is, how the heck do I know if we have onions growing or not!? It has been over a month since we planted."
Shaylen on Saturday 13 April 2013
"Shaylen - welcome to the wonderful world of growing! Onion sprouts/seedlings can be identified by their hooked over appearence. As the seedling emerges it is bent double-back on itself. As it clears the ground, it then 'unfolds' to give the grass-like appearence. Onion sprouts have a rounder profile (if cut through), while grass is flatter. I would suggest that if your seedlings still aren't up they may need re-sowing, as they should have been up with two weeks. Give them another go. And congratulations on your achievements so far!"
Ben Vanheems on Monday 15 April 2013
"Hi Re grass or onions? I used to have the same problem.however a quick bite will soon release that sweet onion flavour - if it is onion! I am now very careful when sowing in the seed bed; first no weeds- clear the lot- grass too. in the "clean bed" I sow rows between two markers- I use lolly-pop sticks (sorry, some folk will call them something different - so what I mean is the wooden sticks found in "popsicles" in the USA I believe - we can buy the sticks in bundles they make excellent plant lables too\) ) or plastic straws to identify just where the little shoots will be. Hope this helps "
peta in france on Monday 15 April 2013

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