How to grow Welsh onions
All you need to know about growing Welsh onions, in our Grow Guide.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
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| Harvest | yes | yes | yes | yes |
Welsh onion, also known as Welsh bunching onion, Japanese leek and stone leek (Allium fistulosum) is a non-bulbing onion, bearing clumps of spring onions with a mild, chive-like flavour. The onions can be added raw to salads, stir-fried and sautéed and can also be used as a garnish. Welsh onion is perennial – simply lift clumps, harvest what you need to and replant, and they will develop new clumps you can harvest from in future.
Although Welsh onions are non-bulbing, they will form small bulbs after being in the soil for several months.
Are Welsh onions the same as spring onions?
'Spring onion' is used to describe how the onion is used, rather than the species. Spring onions can therefore be derived from Allium fistulosum and Allium cepa. Indeed, when thinning out bulbing onions to give them more space to deveop bulbs, you can eat the thinnings as spring onions.
How to grow Welsh onion
Sow Welsh onion seeds in March, into well-prepared, moist but well-drained soil. Welsh onions do best in full sun. Water regularly in dry weather.
Where to grow Welsh onions
Welsh onions are perennial, so bear this in mind when planting as they will be there for several years. They do best in a sunny location and in rich, moist but well-drained soil.
How to plant Welsh onions
Sow Welsh onions direct into well-prepared, humus-rich, neutral-to-acidic, well-drained soil. Alternatively sow into multi-celled trays and plant out after all risk of frost has passed.
Plant in drills 1.5cm (½”) deep, in rows 23cm (9”) apart in growing position. Carefully pull any weeds that come up, so that the seedlings can get established.
Caring for Welsh onions
Welsh onions need very little care. Hoe between rows to keep the area free from competing weeds, and water during dry spells. Mulch annually with home-made compost or well-rotted manure to maintain high levels of soil nutrients. If you don't harvest the onions regularly, it's a good idea to dig them up completely every few years, and divide and replant them. This will increase yields and help maintain vigour.
How to harvest Welsh onions
Harvest Welsh onions from June to October, when they are about as thick as a pencil and around 15cm tall. Dig up the whole plant, taking care not to break the stems. Replant any stems you don't need as they will continue to grow – plant them singly for the best results, as they will clump up and form the following year's crop.
Alternatively, simply trim the greens, leaving the bulbs in the soil. They will grow new stems within a few weeks.
Growing Welsh onions: pests and diseases
Welsh onions are generally pest free but may be susceptible to onion white rot, along with slugs and snails.
Advice on buying Welsh onions
- Check that you're buying Allium fistulosum and not Allium cepa, both of which are sold under 'spring onions'
- Ensure you have the right soil type (neutral to acidic) and a good sunny spot for them to grow
Where to buy Welsh onions
- Thompson & Morgan (seeds)
- Crocus (potted plants)
- Dobies (seeds)
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