Onions are raised either from seed, plants or from sets (small bulbs), each has pros and cons:
Sets Advantages – easier to grow, less prone to pests and diseases, matures earlier. Disadvantages – less choice of variety, more prone to bolting, more expensive.
Seed Advantages – available for all varieties, less prone to bolting, more flexible sowing times, cheaper. Disadvantages: more labour, longer growing season, more susceptible to pests and disease.
Plants Advantages – easier to grow, less prone to pests and diseases and have had a head-start on arrival, meaning a shorter growing season for you. Disadvantages – Less choice of variety, more expensive.
Different types available which have different growing times and methods:
- Autumn planting onion sets: small bulbs which are cleaned, graded and stored, ready to plant out in the autumn. Gives an earlier crop than spring planted varieties.
- Spring planting regular onion sets: small bulbs which are cleaned, graded and stored, ready to plant out in the spring.
- Spring planting heat prepared onion sets: the heat-treatment minimises bolting and extends the growth period, meaning much greater yields can be achieved.
- Autumn planting shallots sets: small bulbs which are planted in autumn and grow to form a cluster or shallots the following summer.
- Spring planting shallot sets: small bulbs which are planted in spring and grow to form a cluster or shallots slightly later in the summer than the autumn-planted sets.
- Autumn sowing onion seeds: Sow in autumn for a crop of onions from early summer the following year. These varieties don’t keep as well as spring sown varieties but are useful for plugging the gap earlier in the season.
- Spring sowing onion seeds: Sow in early spring for a crop of onions from mid-summer through to autumn. These onions can be stored until spring the following year.
- Onion plants: Plant in mid-spring for a crop from mid-summer to autumn.
Bulb onions, such as Red Cross, Troy and Red Barron, can be grown from sets or seed and can be eaten fresh, or dry them out for storage.
Spring onions, such as White Lisbon and Guardsman, are grown from seed. Depending on whether their variety is winter hardy or not, you can sow them anytime between March and October for a long harvest between February and September. They don’t store well but only take around 12 weeks to be ready to harvest and can be sown throughout most of the year.
Site and Soil Onions prefer an open, sunny site with light, free-draining soil. Avoid planting onions in very heavy or freshly manured soil. Onions are sensitive to acidity, so if you know you have acid soil it’s a good idea to dig in lime to the planting area beforehand. For best results, dig a pre-planting fertiliser into the ground.
How to Grow Onions and Shallots from Sets
When to plant Autumn planting onions: September – November Spring planting onions: March – April Autumn planting shallots: September – December Spring planting shallots: February – March
Harvest time Autumn planting onions: June – July Spring planting onions: August – September Autumn planting shallots: June – July Spring planting shallots: July – September
Planting: Both autumn and spring varieties can be planted straight outside into prepared soil. If the soil is loose and well dug you should be able to push the sets into the ground, or use a dibber to create a hole first. Plant them, pointy-end up, in rows at a spacing of about 15cm.The tips of the sets should be just level with the soil surface.
How to Grow Onions and Shallots from Seeds
When to Sow Autumn sowing onions: August – September Spring sowing onions: January – March Spring sowing shallots: January – March
Harvest Time Autumn sowing onions: June – July Spring sowing onions: August – September Spring sowing shallots: August – September
Sowing Autumn-sowing onions can be sown indoors to be transplanted outside at a later date, which will give them a bit of a head start, or they can be sown directly into the growing position. Spring-sowing seeds are usually sown directly into their growing position.
Sowing indoors: For an earlier start, especially in colder areas, sow seed in a cool greenhouse in late winter or early spring. Once the seeds have germinated and are about 1cm tall and at ‘crookneck’ stage, they should be pricked out at a spacing of about 5cm. Start to harden them off once they reach 2-3 leaf stage before planting out into eventual growing position in mid – late spring.
Transplant the seedlings into rows outside in mid – late spring, at a spacing of around 15cm, or allow up to 25cm for larger bulbs.
Sowing outdoors: As soon as the soil is workable in spring, or before it becomes in mid-autumn prepare it by digging and raking it to a fine texture. Avoid sowing into very cold or wet soil. Sow thinly into rows at a depth of about 2cm. The rows should be about 30cm apart from each other. As the seedlings start to grow they will need to be thinned every now and then to create space for bulbs to develop. Use the removed seedlings as spring onions or chives. Once they reach a spacing of about 15cm you’ll no longer need to thin them.
How to Grow Onions and Shallots from Plants
When to plant: April Harvest time: August – September
Planting: Onion plants are delivered in early April when they’re ready to be planted outside. Make sure the soil is well dug and crumbly before planting. Remove the plants from each cell one at a time by pushing them out from underneath. Using a dibber, create drills (the same depth as the plant cell) in rows at a spacing of 15cm. The plants should be planted no deeper or shallower than they were in the cell tray. Firm them into the ground and water-in.
How to Grow Spring Onions
When to sow: Spring onions: March – July Winter hardy spring onions: August – October
Harvest time: Spring onions: May – September Winter hardy spring onions: February – May
Sowing: Sow winter hardy spring onions, such as White Lisbon, in autumn and spring varieties from March. You can continue to sow spring onions throughout summer to provide a continuous harvest. Prepare the soil by digging and raking it to a fine, crumbly texture. Avoid sowing into very cold or wet soil. Sow thinly into rows at a depth of about 2cm. The rows should be about 10cm apart from each other. As the seedlings start to grow they will need to be thinned every now and then, but whatever you remove doesn’t have to go to waste. You can use the removed seedlings as spring onions or chives. Once they reach a spacing of about 2cm, you’ll no longer need to thin them out.
Further Growing Information for Onions and Shallots
Growing: Onions and shallots prefer light soil, but where this isn’t available you can dig a generous amount of grit into the planting area to ensure any water can drain away from the bulb.
Protecting growing onions and shallots with netting should help prevent bird and insect damage. It’s also important to keep the area around them weed free.
Onions and shallots benefit from watering during dry spells in the middle of summer. But generally, once established, they require little attention other than occasional weeding and feeding with a liquid feed.
Harvesting: For fresh use, lift onions when they reach a usable size. If harvesting for storage, wait until foliage starts to die down and the tops bend over naturally. Ease the bulbs gently from the ground. In dry weather you can leave them on wooden benches or boxes to dry outside for a week or so, but if it’s damp you may be better off drying them in a greenhouse.
Harvest shallots from mid–summer onwards. They form clusters of bulbs that should be lifted whole, using the same method as lifting bulb onions.
Spring onions don’t keep for long, so it’s best to harvest them as and when needed. They’re easy enough to harvest without tools, simply by gently easing them from the ground by pulling on them gently.
Storing: Onions and shallots are ready for storage when the skins have gone dry and papery, then they should be kept in a well ventilated place. Our onion storage nets are ideal for storing onions, shallots and garlic, helping to keep them in top condition for as long as possible.
Health Benefits: Onions have been used in the past as a treatment for angina, coughs, colds and asthma. It’s also found to help reduce blood pressure and cholesterol levels.
Onions Pests and Diseases: Rust disease – rusty spots form on the leaves, sometimes killing them off completely, often resulting in smaller bulbs size. This commonly happens when growing onions sit in damp soil for too long, it also happens if grown in soil where either onions, garlic or leeks have been grown before. There isn’t a cure for rust disease, but if you see any leaves with rust-coloured spots on, remove them and throw them away to help prevent the rust from spreading. Don’t grow garlic, onions or leeks in areas that have been affected by rust for 4 to 5 years.
Onion white rot – the leaves turn yellow and wilt, preventing the bulb from forming properly. The bulbs will have white, fuzzy spots on if they have onion white rot. There isn’t a cure, the best thing to do it remove the bulbs from the area completely to avoid the disease spreading.
Onion fly – the leaves start to wilt and turn yellow, preventing the bulbs from developing. Onion fly can affect garlic and leeks as well as onions. The larvae of onion fly live in the soil and eat the roots of the bulb, and eventually burrow into the bulb itself. Discard any bulbs you discover with onion fly. Try preventing onion fly by planting next to carrots.