How To Grow Onions

How to grow onions - close up

The humble onion is one of my favourite vegetables to grow. I don’t think it’s possible to have too many onions. They are great, almost essential, ingredients for a wide range of sauces. I also think they go splendidly in summer salads, especially when accompanying tomatoes.

There are two methods for growing onions:

1) From onion sets or bulbs (immature onions) and planted either in late autumn for overwintering for the earliest possible summer crop, or sown in early spring.

2) More adventurous gardeners will be tempted to grow onions from seed to take advantage of the greater choice of onion varieties available.

Both approaches are described in our how to grow onions guide.

See onions sets available by Suttons Seeds.

How To Grow Onions From Sets

Growing onion from sets can feel like cheating, and with luck will deliver a bumper crop of onions with very little effort. Onion sets are effectively miniature onion bulbs – resembling shallots and only a little smaller – that are simply poked into the ground and left to grow.

The germination rates are excellent. Even though onion sets have been prepared by set providers, it is possible to buy bags of 100 onion bulbs at a fraction of the price it would cost to buy 100 fully mature onions in a shop.

How To Grow Onions – When To Plant Sets

There are two choices:

  • In late September / early October for the earliest possible summer crop the following year
  • As soon as warmer weather arrives in early spring (it’s worth waiting for the sun)

Whichever time is chosen, the planting, care, and maintenance programme is very similar.

How To Grow Onions – Planting Sets

How to grow onions - bed preparation

The picture above shows how I prepare the ground for onions. I like to grow onions and garlic together as they ripen about the same time, and it makes crop rotation easier as they are in the same family. The soil should be weed free, level and relatively loose (rather than in big heavy clumps). My method is to turn the soil over with a spade, and then level and break the soil up with a rake.

The ideal spacing for onion rows is about 10 inches apart to allow plenty of room to hoe away weeds. Six inches is the ideal spacing for plugging the onion bulbs into the soil. They should be placed shoot upwards (thin end upwards) into the soil with only a tiny fraction of their head showing above soil level.

I would strongly recommend covering freshly planted onion sets with a net. Birds will not eat the sets, but they do have an annoying habit of pulling them up. I assume they do this to check what they are and whether onion bulbs are edible.

How to grow onions - watering

How To Grow Onions – Care Of Sets

Apart from needing to hoe in between onions to keep weeds under control, onions are one of the easiest vegetables on the allotment to care for. After the sets have germinated, any protective nets can be removed as the birds will no longer be a problem.

Onions do not require constant watering. Some people even say that too much watering can spoil their flavour. In normal summer weather I will leave them to grow naturally. In prolonged absence of summer rain showers, I may give them a good soaking to tide them over (every 10 days or so). In extreme hot weather they may need watering every 3 or 4 days.

How to grow onions - harvesting

When onion leaves start to turn yellow and fall over they are ready for picking.

Onions grown from sets store slightly less well than onions grown from seed, although this depends on the variety grown.

Before storing, it is recommended to leave onions for a couple of days in sunshine to dry them out. Afterwards, they can be tied together and hung to dry further, or moved to a cooler location and dried on a tray or shelf.

How To Grow Onions From Seed

Growing onion from seed feels more like gardening. Planting an onion set can feel unrewarding. After all, the onions are already formed and already look like miniature onions. All a gardener needs to do is add water. Where as planting from seed has a natural feel, without any intervention of modern technology and heat treatments. It also has some advantages:

  • There is a much wider variety of onion types available from seed
  • They will not be damaged by harsh winter weather (as they are planted in the spring)
  • Once germinated,  they will mature almost as quickly as over wintered onions

How to grow onions from seed - preparing rows

Nevertheless the first hurdle does need to be overcome – that of securing germination. Germination from seed can be a litte unreliable. To maximise success my recommendation is to use fresh seed rather than anything you may have stored or been given. Growing onion seed in an electric propagator can work very effectively.

When is the best time to sow onion seed ? I would delay sowing until spring weather has properly arrived. Warm air and a warm soil with lovely April rain are ideal conditions. Although some people say that onion seed can be planted earlier, I do not think that leaving seed in cold wet soil increases the chance of germination success. My experience is that onions grow very quickly in good weather and will soon catch up with earlier planted seedlings.

I find it easiest to plant three rows and then leave a larger space of about 60 centimetres for the next set of rows.  This space allows me to walk up and down between the rows when weeding and watering.  To plant the seeds,  I create a small trough with a hand trowl – you can see the shallow troughs in the picture above,  and then sow the seeds about one every 5 centimetres.  When the onions grow I will then thin to create a 6 inch or 15 centimetre space between each seedling.

How to grow onions - young plants

When onion leaves start to turn yellow and fall over they are ready for picking. On the right hand side of the picture it is possible to see garlic that has reached this stage.

Before storing, it is recommend to leave onions for a couple of days in sunshine to dry them out, and then spread them out or hang them in a warm, dry location for several weeks before bagging in nets.

Depending on the variety grown, onions can store either to the end of autumn, or through the winter months. This is worth checking before growing!

See onions sets available by Suttons Seeds.

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