How to grow onions

I  like growing Onions because they are an easy crop. In a bad weather year, when growing vegetables is difficult, you can always rely on onions.

The easiest way to grow onions is from sets, which are tiny onion bulbs which have been treated to produce good bulbs. The treatment also reduces the possibility of the onion producing a flower and bolting.  The best time to plant onions is mid to late March or April, depending on the spring weather when the soil is a bit drier and warmer. You can buy onions suitable for planting out in the autumn and over wintering, provided that your plot is well drained, ideally with some added organic matter. As with all bulbs, winter wet can cause the bulb to rot. To grow onions, the ground doesn't need to be really finely raked as it does for carrots and salad crops, just reasonable and not compacted.

Onions keep well so you can pick and use throughout the winter.  Provided you store onion sets somewhere dry and cool, you can also carry over spares to the next gardening season. Onion sets are often sold in quite large quantities, 50+ it is helpful to know they will keep from year to year.

 video How to plant and grow onions and garlic

green wheelbarrow easy to grow

Onions are very easy to grow, they almost grow themselves

How to grow and plant onions

Onion sets are the easiest, although you can raise from seed if you have time and inclination. You can grow onions in containers. However, they need a lot of space, about 10-12 cms apart and 30 cms between rows, which would necessitate a large planter. For containers garlic is more suitable. If you do plant in containers and by necessity plant closer together, the onions will be smaller.

Onions are a bulb, so when planting the hairy bulb end goes downwards. Make a small indentation in the soil. You can easily use a finger or a dibber, and place the bulb down so only the top tip of it is showing above ground. It is important to appreciate that onions sit just under the soil with a tiny top bit pointing out of the earth. Make a small indentation and ease in gently as the growing source is the hairy bulb end and if you damage it when planting, you may slow the growth. Also, if you push the bulb in, onions have a tendency to push the bulb back out again when it roots. In a raised bed /good soil plant rows each about 10cms apart.

Growing onions is easy and onions have very few enemies in terms of pests, but they have one terror; the pigeon. Over to the plot it waddles and pecks out the little tab of Onion set above the ground and yanks out the bulb. They are a menace. If you have a lot of pigeons in your area, you will need to deter them by covering the onions with a cloche /netting, and keep some spare bulbs to replace the pigeon pecks.

If you are interested in the aesthetic appearance of your veg plot, planting red and white/brown onions in patterns in rows looks attractive. Some veg plots, as seen in the show gardens such as at RHS Harlow Carr, are really inspirational. A more practical reason for planting in tidy straight rows is that you know everything outside the row is a weed which makes the weeds are easier to find and dispose of. (see best gardening tips)

 A row or two of sweet peas to bring in the pollinators adds colour and looks lovely. If your garden shed is next to the veg plot, the side of the shed is an ideal place for a bit of trellis and a few sweet peas. If you have no border, use a trough and fill with rich compost as sweet peas are greedy. More about growing sweet peas

Which Onions are the best onions to grow

In 2013, the RHS undertook a plant trial of onions in which 21 different onion types tested and assessed for bolting, size, yield and 25 of each were stored in a uniform way to test for storage quality. After that, 12 were awarded the AGM.

Following these trial buying onions with the RHS award is an easy way to pick a good variety and those which were given the award were:  Red onions Marshals Red Fen, Red Baron, and Garnet.  Heat treated yellow and brown skinned onions Rumba: not heat treated Sturon, Centurion, Hercules, Autumn Gold Improved, Griffon, Setton, Vulcan, and Turo.

Curiously, nearly all of the AGM were not heat-treated and the trial suggests that it does not in practise make any difference.  The trial gives good guidance as to reliable variety to buy and grow.

Harvesting and Storing Onions

In September, the tops of the onion plants turn golden brown and look like dry growth rather than green growth. When this happens, the onions are ready to harvest. Harvest Onions on a warm day or preferably a warm spell, lift them and sit on the warm dry earth for a few days to dry out throughly and then store in a cool place in string bags.

All these references to "warm" is all very well but our weather does not always oblige. If the weather isn't good, and you cannot dry onions outside it is still important that onions dried before storage. If the weather is poor, another possibility is in the greenhouse where the slats make an ideal spot to dry them out for a week or so before bringing in to store somewhere light and cool. Or put into a string bag and hang up. You can dry onions, garlic and shallots in this way, as shown below. Any moisture will cause the bulb to go mouldy. Onions need to be stored in a cool light environment, an unheated conservatory, garage or porch is suitable. The overwintered variety does not store well.

last updated 16.02.2022