The basis of so many delicious dishes, onions (Allium cepa) are an essential ingredient in every cook’s store cupboard. With so many tasty types of onions available, why not grow your own and try some of them out? Follow our simple guide to growing onions.
The best onion varieties to plant
With so many types of onions available, it can be difficult to choose which one to grow! Here are a few of our favourites:
- Onion ‘Stuttgarter Giant’: produces firm, tasty, slightly flattened bulbs, good for storing.
- Onion ‘Red Baron’: a late maturing variety with dark red bulbs, stores well.
- Onion ‘Jetset’: an early maturing variety with yellow-brown bulbs, stores well.
- Onion ‘Sturon’: a reliable variety with good bolt resistance, producing flavourful round bulbs that store well.
- Onion ‘Troy’: suitable for autumn planting, with good bolt resistance, producing tasty yellow-skinned bulbs.
Should I Grow Onions from Seed or from Sets?
We prefer planting onion sets over starting them from seeds, simply because the sets establish quickly and are easier to plant. Onion sets are small onion bulbs that are sold specifically for gardening. Once planted, they develop into a full-size bulb after about 3½ months.
Also, onion sets can be planted without worry of frost damage and have a higher success rate than planting from onion seeds or transplants.
Of course, starting onions from seed is certainly doable, and may even be necessary in colder regions (Zone 5 and colder). If you’d prefer to try this method, check out our tips for growing onions from seed indoors.
When to Plant Onions
- Onions can be planted in both the spring and fall. Generally speaking, plant onion sets outdoors when the weather is cool—not cold.
- A fall-planted crop of onions needs at least 4 to 6 weeks of warm temperatures to become established in the ground. They will remain dormant during the cool season, but be all primed and ready to grow when spring arrives.
- In regions with a frigid winter, be sure to plants onion sets in the spring as soon as the ground can be worked—usually in March or April. Ideally, time your planting so that outdoor temperatures no longer dip below 28°F (-2°C) after the onions are in the ground.
- Fall-planted onions are a great way to enjoy an earlier and larger bulbed harvest from next year’s garden. Plant in the warm autumn soil so that they may establish a strong root system before winter sets in. As the cold chill of winter arrives, the crop goes dormant. Then, as the temperatures and soil warm again in early spring, the onions come back to life.
- If starting onions from seeds, start them indoors about 6 weeks before you plan to transplant them to the garden. Onion seeds need temperatures of at least 50°F (10°C) to germinate properly.
How to Plant Onions
Planting onion seeds can take more time, so germinate your seeds indoors first to get the process going:
- Prepare. Fill a planting tray or other appropriate container with moist soil and dig furrows half an inch deep for your seedlings. Cover lightly with soil and keep the temperature warm, around 60 to 70 degrees Fahrenheit.
- Transplant. When your onion seedlings germinate (anywhere from a few days to a few weeks), they are ready for transplanting into your garden. Dig holes about two inches deep and four to five inches apart for your onion transplants, in rows that are 12 to 18 inches apart.
- Companion plant. Cabbage, tomatoes, leeks, and carrots all make good companions for your onion crop. Keep helpful plants nearby to bring in beneficial insects and other organic defenses.
- Add mulch. Laying mulch or other organic matter between your onion rows can help smother weeds and retain some moisture for your soil (lessening the amount of watering you need to do).
You can plant onion seeds or plant onion sets. Onion sets are small onion bulbs that can be planted and grown into full-sized bulbs after a few months. If planting onion sets, you can bury them one inch under the soil in your vegetable garden, two to six inches apart. Don’t compact the soil around the onions, just loosely cover the onion bulb.
Caring for Onions
Onions can be left as they are or thinned out once the plants have grown a little to give bigger bulbs. You may enjoy these thinnings in any way that you would like, such as using them for green onions!
Onions are shallow-rooted plants that need to be kept moist in order for their roots not get damaged. It’s important you keep an eye out on weeds, hoeing carefully between rows then hand weeding within the row so as not to damage any onions’ crowns.
When to Harvest Onions
The ideal time to harvest mature onions is late summer, before the weather turns cool (they can grow in colder conditions, but once mature they’re prone to spoiling). Onion tops will turn yellow and fall over when they approach their final ripening stage.
How to Harvest Onions
When harvesting onions, look for brown onion tops crowning their heads through the soil—you can pull these directly from the ground. Store onions in a cool, dark, dry place. Onions that have sprouted flower stalks are already mature, and should be pulled right away and used immediately.
