Onions and shallots can be grown from seeds or sets, the choice is yours and depends on your set up and i have listed the options below. I get equal success with both but generally i like sowing from seed so have a look at the sowing instructions a bit further down.
Easy Option 1 – Indoors
The usual and most reliable option is to sow indoors in trays very early in January or February, with some heat, so that they get going early enough to make nice big bulbs. They will grow on without heat (for example in a cold frame or unheated greenhouse) once germinated. Transplant out about 4″-6″ apart once the soil warms up:
Easy Option 2 – Outdoors
The other common way is to sow seed outdoors directly, in this case you should wait until March or so when the soil has warmed up a bit. (Your onions will be a bit smaller as they’ve had a shorter growing season.) Thin your rows in stages to about 4″-6″ apart as they grow:
Harder (but bigger onions) Option 3 – Overwinter
The final option – more of a gamble, but can give really large onions. You can sow seed outdoors in mid August, with a cold-hardy variety that will survive the winter outdoors. If successful, this can give an early crop of very large onions the next summer. The only other thing to remember is that Onions HATE shading. If they get shaded by other plants like grass or weeds, they won’t bulb properly. It’s easy – just keep them well weeded.
- I think sowing from seed gets better results than growing from sets.
Sowing Instructions:
Using a module tray pre-filled with multi-purpose compost and pre watered, sow a few seeds per module ( called multi sowing ) from January to March or if you are sowing direct, then sow March. I like to water down the compost first to settle it and then do a top up, you’ll find the compost shrinks down once watered. Sow approx 5-6 seeds in each module.
Lightly press seeds down and cover with a thin layer ( approx 0.5cm ) of compost, water once more lightly using a sprinkler so as not to disturb the seed.Sowings in January will benefit from heat such as a heat mat or heated propagator, once geminated you can then move them off heat to an area of good light.
Once germinated thin (i.e. remove the smallest ) so you have just 4 strong seedlings, you can plant them out as a group without thinning( this is called multi-sowing).
From sowing, planting out would be approx. 4 weeks, when planting out multisown veg you do need to allow more room, so plant 25cm apart. Early plantings will benefit from being covered with fleece when first planted until March. Onions and shallots sown this way will naturally push away from each other and grow very well in clumps, its a great way to get more in your space too.
- If you want to use sets then sow end March, beginning April to avoid them bolting ( getting a flower – this will means they stop growing). Use a dipper to make holes and sow the bulbs fat end down, pointy end up. Plant at a depth of the bulb with just the tip of the pointy bit exposed and space them 12cm apart.
