Onions are very easy and cheap to grow, with just a little work and a couple of pounds you can grow hundreds of onions that will last an entire year.
When it comes to growing onions many people automatically assume that growing onions from sets is the way to go, however growing from seed gives a more reliable crop that is less likely to bolt and will store for at least 9 months. I’d always recommend growing onions from seeds rather than sets.
There are a lot of wonderful varieties that can be grown from seed with the range being far greater than sets. You can also find a range of seeds that are grown as giant onions which are great for shows or just grown for bragging rights.
Planting Onions From Seed
Sowing can begin as early as February indoors for large onions, with sowings in March producing average sized onions and those sown later in April giving small onions which are handy in the kitchen.
Two inch plugs, soil blocks or deep roottrainers are ideal for sowing seeds in. A good multipurpose composts should be used as this will have all the nutrients needed to get the plants growing strongly over the coming weeks.
Sow two seeds per pot and cover with a very fine dusting of compost. A light watering will make sure there is a good contact between the seed and soil which is essential for good germination.
Germination for onions can take up to two weeks but once the seedlings are big enough to handle they should be thinned to just one plant per container.
These plants need to be kept indoors for several weeks, a windowsill or unheated greenhouse are best suited to this.
Transplanting Onion Plants Outdoors
Once the plants are established in their pots they can be transplanted outdoors. If the plants are hardened off over a week they are hardy enough to survive most cold weather, planting out 4 weeks before the last frost date is fine.
The soil is important for onions as they are quite heavy feeders. Adding an two inch layer of rotted manure or compost over the growing bed gives the plants a really good start. A handful of blood, fish and bone per square metre has been recommended by old gardeners for decades.
Plants should be spaced 6 inches (15cm) in rows 12 inches (30cm) apart. Firm the plants in well and water well.
Looking After Your Plants
Onions are tough plants and will grow away steady over several months.
The plants do not have a lot of leaves so weed competition can be a problem, weeding every two weeks is essential to ensure that the plants are not totally taken over by the weeds.
Watering when dry is essential to keep the onions growing strong bulbs, especially in July and August. Although watering at an allotment or veg garden can be difficult and time consuming with onions it is well worth the effort of giving the plants a very good watering every couple of days in really dry weather.
I do not recommend feeding with a liquid fertiliser as I’ve found this leads to the bulbs splitting or going to seed.
It’s easy to see when onions are ready for harvesting as the leaves will begin to fall - this is usually in August or September. Once the leaves begin to fall they can be left in the ground for the foliage to go brown or can be removed somewhere indoors to dry off. Leaving the onions to dry and the tops to go brown is essential for good storage.
Onions that are put into storage are best hung in the traditional manner and kept somewhere cool. Stored in such a fashion the onions can be expected to store for 9 months with most good storing varieties still being suitable for eating a entire year later.