RHS Growing Guides
How to grow salad onions
Our detailed growing guide will help you with each step in successfully growing Salad onions.
Getting Started
Month by Month
| J | F | M | A | M | J | J | A | S | O | N | D | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sow | ||||||||||||
| Harvest |
Choosing
There are many varieties to choose from, either cylindrical like mini leeks or with small round white bulbs topped with green leaves. For added decorative appeal, there are also varieties with reddish-purple bulbs.
Choose hardy varieties for early or late sowings.
For the most reliable varieties, look for those with an RHS Award of Garden Merit (AGM) – see our list of AGM fruit and veg (salad onions are listed under onions).
What and where to buy
Salad onion seeds are widely available all year round from garden centres and online seed suppliers.
Recommended Varieties
Attractive, deep-purple-skinned bulbs contrast well with the dark green leaves. It has a mild flavour and crisp texture, and...
A British-bred, F1-hybrid salad onion, this variety is a cross between ‘White Lisbon’ and a Japanese onion....
Unusual burgundy-red bulbs and deep green leaves with a mild flavour. Great for adding colour to salads.
Sowing
Sowing outdoors
Sow spring onions outdoors from March onwards, for harvests through summer and early autumn. Sowing small batches every couple of weeks will give you continual supplies.
You can also sow hardy varieties in late summer and early autumn for harvesting the following spring. These will germinate and grow into small, sturdy plants before winter and should be ready to harvest from March onwards.
Choose a sunny growing site, ideally with light, free-draining soil. Prepare the ground by weeding and raking to remove lumps and stones. Make a shallow drill, 1cm (½in) deep, then water along the base. Sow the seeds thinly along the drill, then cover with soil. Space rows 10cm (4in) apart.
Protect seedlings from slugs and snails, especially in damp weather.
Thin out the seedlings if necessary, until they are about 2.5cm (1in) apart. Closer spacing may encourage downy mildew. The thinnings can be used in salads.
Seeds can also be sown in large containers, at least 30cm (1ft) wide, filled with multi-purpose compost. Water to thoroughly dampen the compost, then scatter the seeds thinly and cover with about 1cm (½in) of compost.
Sowing indoors
You can make early or late sowing in a greenhouse, either in the greenhouse border or in containers, to extend your cropping season. Sow in early spring or late autumn. Use the same sowing methods as for outdoor sowing, above. Water regularly.
Plant Care
Watering
Water if the soil or weather is dry. Plants in containers need regular watering, as they dry out more quickly.
Weeding
Salad onions grow less well if they have to compete with weeds for light and moisture, so weed regularly – hoe between the rows and hand weed between individual plants. Overcrowding due to weeds also encourages downy mildew.
Mulching
Spread mulch, such as garden compost, around the plants to hold moisture in the soil and keep weeds at bay.
Winter protection
Protect plants sown outdoors in late summer or autumn with cloches or fleece during winter, especially in harsh weather or in cold locations.
Harvesting
Salad onions take about two months to reach harvesting size. They’re best when small and young, about 15cm (6in) tall, with the bulb no more than 1–2.5cm (½–1in) across. If left to grow larger, they will develop a more robust flavour.
Simply lift individual onions whenever required. You can harvest from spring right through to autumn by making repeat sowings.
Problems
Salad onions are generally trouble free, although they can be affected by various fungal diseases, including onion white rot and onion downy mildew, especially in damp growing conditions.
Onion fly is a fairly common problem, especially in dry weather, while slugs and snails can be troublesome in damp conditions.
Get involved
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