Very popular vegetables for the allotment gardener. Onions (Allium cepa) and their smaller cousins shallots, can be easily grown from seed or from sets (small bulbs). Although cheap to buy in the shops, you will discover a much broader range of varieties available in seed catalogues, in varying degrees of pungency and flavour.
Soil Type: Rich, fertile, moist but well-drained, non-acid soil.
Conditions: Grow in a sunny, open position.
Ease of Cultivation: Easy
Type: Bulb Vegetable.
Hardiness: Hardy in most regions of the UK.
When to Sow: Sow over-wintering crops in August. Plant maincrop sets in March and April.
Harvest: Mid or late summer. Around 20 weeks after planting.
Onions are normally grown from sets (small bulbs), which are easy to grow from. They are quicker to mature that sown seed, less prone to disease and crop better in poorer soils.
Growing onions from seed is cheaper than sets and many more varieties are available. Although sown seed will take longer to mature and is more prone to bolting.
Certain varieties can be over wintered, usually
known as Japanese onions.
They don't store as well but can extend the
fresh harvest season by a few months.
Grow in a fertile, well-drained, crumbly loam with a pH of 6.5 or above. Ensure the soil is not too soggy as a heavy wet ground will encourage fungal rot.
Do not add manure before planting but follow a crop that was manured in the previous season.
Dig over to a fine tilth and allow the soil to settle. Apply a general purpose fertilizer a week before planting.
Plant maincrop onion sets and shallots from March to April. Space in rows, 6in (15cm) between plants. Closer spacing can be used to produce smaller bulbs. Prepare the planting hole with a small dibber or draw a small trench and plant the sets so the tip is just above soil level. Do not push the sets into heavy soil as this can damage the root plate.
Net or cloche newly planted sets to prevent birds from pulling them out.
Onions from seed should be sown earlier to give them longer time to mature. They can be sown under glass in January or February, in trays or modules. Once germinated keep the temperature around 10-15°C to prevent bolting. Harden off before planting out. Space as for sets, at 6in (15cm) between plants.
Sow Japanese onion seeds in August or plant sets from mid-September to early November, ready for lifting in June.
Keep weed-free and water regularly in dry weather, until ready for harvest. Do not over water as this can delay swelling of the bulbs and make them more susceptible to disease. Take care when hoeing to avoid damaging the bulbs.
Onions are prone to fungal diseases, rust, smut, downy mildew and white rot, particularly in wet weather. The main pest is the Onion fly and eelworm. Onions grown from sets are usually less susceptible.
Harvest when large enough for use or when the foliage has died down - approximately 20 weeks after planting.
When growing onions to store, wait until the foliage begins to die back and bends over on its own accord. Gently lever up the bulbs with a fork and dry-out thoroughly for storage. Ideally, dry for a few weeks on a rack so that air can circulate all around the bulbs.
Once fully dried, string them up together or place in net bags and hang in a cool, dark place. If kept well, stored onions can last for up to 12 weeks. Check regularly and discard any that are showing signs of rot or mould.
Prepare by trimming off the neck and roots and peeling away the dry, papery outer layer. The bulbs can then be, sliced, chopped, diced or cut into wedges. Shallots can be sliced or left whole.
Onions are very versatile in the kitchen and can be added to recipes for soups, stews, pies, casseroles and sauces or fried as an accompaniment for burgers and hot dogs etc. Mild onions can also be eaten raw in salads.
Shallots (which are milder in taste) are often roasted or added to a oven baked recipes. Mild silver skin or pearl onions and small shallots are good for pickling.
Small or sliced onions can also be frozen, if necessary. Wrap well and seal to prevent the odour escaping. Use within 6 months.
Onions are a good source of vitamin C and B vitamins. The pungent flavour indicates they are full of the polynutrients and antioxidants.
Onions are available as seeds or as 'certified' (disease and virus free) sets. Heat treated sets have the added bonus of a reduced tendency to bolt (run to seed).
Onion 'Ailsa Craig' (Heritage Variety) large globe shaped onions with a mild flavour that is good in cooking and raw dishes. Ideal as a showing variety or for general cultivation. Can also be autumn sown. Good for storage potential. Available at Van Meuwen and Thompson & Morgan.
Onion 'Bedfordshire Champion' a very old and reliable variety that is ideally suited to the UK climate. Large globe shaped bulbs with crisp white flesh. Available at Thompson & Morgan.
Onion 'Centurion' (F1 Hybrid - RHS Award of Garden Merit) developed from the popular 'Sturton'. It is a good, early maturing heavy cropper with smooth straw-coloured skin. Stores well.
Onion 'Electric' (Autumn Planting) a good over-wintering red variety that provides semi-globe shaped onions with pink tinged flesh. Harvest from late May to July. Excellent in salads and stir fries. Stores well. Available at Van Meuwen.
Onion 'Garnet' (Spring Planting) a high yield maincrop variety with firm round, dark red bulbs. Available at Thompson & Morgan.
Onion 'Hi Keeper' ideal for over wintering or as spring sown. Good as a showing variety or for general cultivation. Available at Thompson & Morgan.
Onion 'Hercules' (F1 Hybrid - RHS Award of Garden Merit) produces high yields of elongated round bulbs with golden skins and firm, rich flesh. Strong flavoured and resistant to bolting.
Onion 'Hylander' good resistance to fungal disease. Available at Thompson & Morgan.
Onion 'Isobel Rose' rose-pink bulbs ideal for UK growing conditions. Stores well. Available at Thompson & Morgan.
Onion 'Paris Silver Skinned' easily grown from seed and quick to mature even on poor soils. Ideal for pickling or cocktail onions. Available at Thompson & Morgan.
Onion 'Red Baron' (Spring Planting) a classic pink/purple ring fleshed variety, with medium sized dark red bulbs. Mid to late maturing. Has a strong flavour that is sweeter tasting than most white varieties. Ideal sliced on salads. Stores well. Available at Thompson & Morgan.
Onion 'Red Herald' (F1 Hybrid) produces a strong flavoured, deep red, rounded bulb. Available at Thompson & Morgan.
Onion 'Setton' (RHS Award of Garden Merit) an improved version of the popular large globe 'Sturon' variety. Good for storage. Available at Thompson & Morgan.
Onion 'Sturton' is a large globe shaped onion with golden skin. A good rich flavour and long storage potential. Available at Van Meuwen.
Onion 'Stuttgart Giant' (Spring Planting) a popular variety that produces firm, semi-flat bulbs with a fine flavour. Available at You Garden.
Onion 'Vulcan' (Early Spring Planting) fast cropping brown onions with round bulbs that have thinner necks and good resistance to bolting. Available at Thompson & Morgan.