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Indoors | Outdoors

Why Grow It

We love onions at GIY because they are one of those vegetables that it’s possible to become fully self-sufficient in, even if you don’t have a huge amount of space. A decent sized raised bed could produce a couple of hundred onions, which would be enough for most families for up to a year.

Onions are relatively easy to grow and they store well. Above all, there’s nothing better than having onions hanging in your shed and knowing you don’t have to buy those dry, tasteless, imported supermarket onions this year.

  • Onions grow best in a good fertile soil, so add compost and a general fertiliser for best results.
  • There are two types of onions: autumn-sown onions and the far more common spring varieties.
  • Onions can be grown from seed or small, dried immature onions called ‘sets’. Beginners often find growing from sets easier.
  • To grow from sets, buy good quality sets in either the autumn or spring. Plant autumn varieties in September or October and spring varieties in late March or April.
  • Push the sets into the soil up to their necks (top of the little bulb where the tufty bit starts) in rows 25cm apart. If you want bigger onions, and a lower overall yield, plant the sets 10cm apart; for a higher yield of smaller onions plant then 5cm apart.
  • Seeds (of spring varieties) need to be sown early in the year in January or February to ensure a good yield.
  • Seeds are sown in modules. Sow four seeds in a module, 1cm deep. The seeds will need a heated mat or warm windowsill to germinate. After germinating they will grow in an unheated greenhouse or polytunnel.
  • Spring varieties will be ready for transplanting in 6 to 8 weeks when they are 10-15cm high. Transplant 25cm apart with 25cm between rows.
  • You can sow more seeds (8-12) in a module and thin each one out to four plants around two months after transplanting for a crop of scallions.
  • Onions hate weed competition so keep your onion bed weed free. Hoe carefully between the rows as weeds emerge and hand weed along the rows.
  • Onions can be harvested at any stage you want to eat them, from scallion size to green onions to mature dried onions.
  • For mature onions, pull carefully out the ground after the leaves have fallen over in August, and leave outside to dry for a week or two.
  • In a damp autumn the drying will need finishing in a dry shed or poly tunnel.
  • When completely dry store the onions in a dry shed – they store better if left untrimmed.
  • Golden Bear F1
  • Santero F1
  • Young transplanted sets appear irresistible to rooks who pull the young plants out the ground – this is easily prevented by using netting.
  • The most serious disease in onion is white rot – this is usually brought into the garden on sets. The disease causes the onion to rot from the base. Dispose of diseased onions away from your garden, as the disease will stay in the soil for a decade or move. It also means you can’t grow onions, garlic or leeks in that area of your garden for 10 years.
  • Downy mildew is a disease that can attack the leaves. To control this keep the onions growing healthily, but don’t over feed with nitrogen.
  • Try baked onions – leave skins on, cut in half and bake for 45 mins. Yum!
  • If your onions ‘bolt’ and produce a flower spike on the stalk, remove it immediately.