Given the right conditions, onions and shallots are very easy to grow and reward little effort with a good crop. They’re one of the most versatile vegetables in the kitchen, too. Onions are a large family of strongly flavoured biennial and perennial plans.
Depending on when and how you grow them, you can achieve a crop that can be harvested from as early as June right up until October, and many varieties, such as Sturon andStuttgarter Stanfield, will keep until the following spring.
Seeds, sets or plants?
Onions and Shallots are raised either from seed, plants or from sets (small bulbs), each has pros and cons:
Onion & shallot sets:
- Advantages: easier to grow, less prone to pests and diseases, matures earlier
- Disadvantages: less choice of variety, more prone to bolting
Onion & shallot seeds:
- Advantages: available for all varieties, less prone to bolting, more flexible sowing times
- Disadvantages: more labour, longer growing season, more susceptible to pests and diseases
Onion & shallot 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 and more expensive
How to grow onions
Autumn planting onions and shallots
When to plant onions and shallots
These onion and shallot varieties you plant in autumn for a crop in mid-summer the following year. The advantage of these varieties is that you are planting in soil that has been naturally warmed up over the summer, so they settle well and they are set up to tolerate cold winters.
How to plant onion and shallot sets
In September to November plant sets pointy side up straight into the soil outdoors at 7-10cm (3-4in) intervals in a row, and space rows at 30cm (12in) apart.
Plant in an open, sunny site in fertile soil that is well-draining yet moisture retentive.
Incorporate bulky compost into the soil in the spring before to increase the soils fertility levels and create good soil texture, without it being too rich.
How to feed and water autumn planted onions and shallots
Apply bulky compost earlier in the season to planting- this will increase the fertility of the soil without it being too rich. Avoid adding freshly incorporated compost as this can create a soil which is too rich.
In spring, you can boost post-winter growth by applying a seaweed-enhanced feed, rich in phosphorous for stimulated root growth and encourages full and flavoursome bulbs.
Water at planting in autumn and reduce watering overwinter. In spring water lightly as the weather warms but stop again once the bulbs are actively swelling.
A well-textured soil with incorporated bulky compost will hold on to enough moisture to see the crop through the overwintering and growing season.
Temperatures for autumn planted onions and shallots
You can plant sets straight into the open soil in autumn as the ground has been adequately warmed up over summer. Bulbs will appreciate an open and sunny site.
If exposed to temperatures that are too low, there is a risk of bolting which means that plants produce flowers at the expense of harvestable bulbs.
Varieties that are suited to autumn-planting are hardier to cold temperatures and less prone to bolt.
How to harvest and store onions and shallots planted in the autumn
Harvest bulbs from early to mid-summer (June to July). Follow these steps for harvesting shallots:
- lift with a border fork once you notice the leaves have gone yellow.
- Separate the clusters, clean off soil and grit, and dry in a cool light place for one to two weeks.
- In wet weather bring into a garage by the window. In dry, sunny weather leave outdoors or in a well-ventilated greenhouse.
For onions follow these steps:
- Lift when the foliage has wilted and yellowed.
- Lift carefully with a border fork, dry in a cool, light place for two to three weeks before using in the kitchen.
- Store in a cool place. Plaiting onions and hanging them is a space-saving way to keep them drying, and off the ground away from pests.
Best varieties of autumn-planting onions and shallots
- Onion ‘Red Cross’ - Produces large bulbs with deep red skin and white flesh with clearly defined red rings. Overwinters well and stores for up to 3 months.
- Onion ‘Radar’ - Radar is loved for its mild flavour storage potential; under the right conditions it will store for about a year.
- Shallot ‘Biztro’ - Spicy flavoured, strong growing shallot, with beautiful pale red flesh.
Common pests and diseases
It’s important to be aware of the following common pests and diseases when growing onions and shallots:
- Onion fly – Early signs of onion fly include the yellowing of leaves on established plants. Once this pest takes hold seedlings are often killed in patches. Any effected plants/blubs should be lifted and burnt to prevent further problems.
- Bulb rot – Often occurs in warmer soil temperatures during the summer months. Plants will begin to yellow and the tips of the leaf’s will die off. The plant will have missing roots, or remaining roots will appear brown and rotted.
- Smut – A fungal disease that can be identified by black blisters on the plants leaves, seedlings are often killed within a few weeks and surviving plants suffer stunted and distorted growth.
- Shanking – A disease that causes leaves to yellow and shrivel up and bulbs to become soft.
Spring planting varieties
These onion and shallot varieties you plant in spring for a crop in late-summer to early-autumn that year. The advantage of these varieties is that you have a store of flavoursome onions over the winter when home-harvests of other crops are low.
Heat-prepared sets have been treated to prevent bolting, which is when the onions flower at the expense of producing harvestable bulbs.
How to plant onions and shallot sets in the spring
In March and April plant onion sets pointy side up straight into the soil outdoors at 15cm (6in) intervals in a row, and space rows at 25cm (10in) apart in an open, sunny site in fertile soil that is well-draining yet moisture retentive.
As with autumn planting incorporating bulky compost into the soil will achieve this, with increased fertility levels creating good soil texture, without it being too rich. This should be done in the autumn/winter.
Watering and feeding
Water at planting in spring and more so as the weather warms as the season continues. Stop again once the bulbs are actively swelling. A well-textured soil with incorporated bulky compost will hold on to enough moisture to see the crop through the growing season.
In late spring, you can boost post-winter growth by applying a seaweed-enhanced feed, rich in phosphorous for stimulated root growth to encourage full and flavoursome bulbs.
You can plant sets straight into the open soil in spring. Bulbs will appreciate an open and sunny site. If exposed to temperatures that are too low, there is a risk of bolting which means that plants produce flowers at the expense of harvestable bulbs.
Heat treated spring-planting varieties are less prone to bolt and flowering at the expense of producing harvestable bulbs.
Harvest bulbs from late summer to early autumn (August to September). As with Autumn planted shallots, lift using a border fork once the leaves have turned yellow. Separate the clusters, clean off any soil and dry in a cool light place for one to two weeks.
For onions the same steps can be taken as those planted in the autumn, life with a border fork when the foliage has wilted and yellowed. Store in a dry, cool light place for two to three weeks before using in the kitchen.
Best varieties of spring-planting onions and shallots
- Onion ‘Red Fen’ – Heat-prepared making them resistant to bolting, a uniform round shape and deep-red colour with a good flavour. Ready for harvesting in August and September.
- Onion ‘Red Baron’ – Stronger flavoured than our other onions, red baron stores well from September until the following April.
- Onion ‘Stuttgarter Stanfield’ – Slow to bolt so suitable to plant sets as early as January for harvests as early as August.
- Shallot ‘Jermor’ – Famed in the growing world for its long, oval bulbs that make easy slicing in the kitchen. Enjoyed in the home-growing world for its sweet flavour and uniform bulbs that make easy picking from July.
How to grow onions and shallots from plants
When to plant: April
Harvest time: August – September
Planting onions and shallot plants:
- 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 Onions and Shallots from Seeds
When to Sow
Autumn sowing onions: August – September
Spring sowing onions: January - March
Spring sowing shallots: January – March
Autumn sowing onions: June – July
Spring sowing onions: August – September
Spring sowing shallots: August – September
How to sow onions and shallots from seeds
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.
- 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 onion and shallot seeds 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 Spring Onions
When to sow
Spring Onions: March – July
Winter Hardy Spring Onions: August – October
Spring onions: May – September
Winter hardy spring onions: February – May
Sowing spring onions
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. and at 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.
For Best Results
Try our onion fertiliser, which is specially formulated to give onions all the nutrients they need to produce healthy growth.