How to grow onions – an easy beginner’s guide
- By: Ashley Saunders
- May 2020
If you’re just starting a veg patch, you should try to grow onions! They don’t take up much space, so can either be planted between rows of other veg or grown in containers.
The health benefits of onions are numerous as they’re high in vitamin B, vitamin C, fibre and potassium. Onions have been linked to a reduced risk of cancer, lower blood pressure, and increased bone health.
Here’s how to grow onions in your vegetable patch and ensure a plentiful supply throughout the year!
Interesting onion facts!
Onions are mentioned in the Bible as one of the foods the Israelites ate.
Ancient Egyptians worshipped the onion!
Onions really do make you cry. That’s because they contain sulphuric acid.
In the Middle Ages, onions were an acceptable form of currency. You could use onions to pay rent, goods and services. Some even gave them as gifts!
According to the Guinness World Record, the heaviest onion weighs 8.5 Kg and was grown by Tony Glover in 2014.
Libya is the country that eats the most onions per capita!
Onions need full sun and don’t like to be shaded by other plants. So choose the sunniest spot in your veg patch to grow onions or if growing in containers, place them where they’ll get good coverage of sun each day.
For bulbs to fully develop, they need well-drained, loose soil. If you have rocky or clay soil, work in some aged manure or compost to improve it.
In early spring before planting, cover the soil in either aged manure or compost and allow it rot it. Onions are heavy feeders which need constant nourishment to produce big bulbs.
When planting onions, it’ worth mixing in some nitrogen fertilizer as this will help you to grow onions successfully.
If you’re looking to grow onions, thankfully, there are a superb range of varieties that are easy to grow. The RHS recommends growing the following varieties:
Noted for it’s dark-skinned bulbs, Setton always produces an excellent yield and they store well.
Quick to grow, Hercules is a large onion with dark golden skin.
A late-maturing red onion with attractive crimson bulbs, which stores well over winter.
Long, slender white stalks which don’t form into bulbs, this onion is perfect for salads and stir-fries.
Storing well over winter, this is a popular and reliable onion with excellent flavour and medium-sized bulbs.
While you can grow onions from seeds, we recommend starting with onion sets as these can be planted without having to worry about frost damage. Onion sets also have a higher rate of success compared to seeds or transplants.
Typically, onion sets take around 3 to 4 months to develop into full bulbs that are ready to be harvested.
If you decide to grow onions from seeds, you’ll need to plant them indoors about 6 weeks before you plan to transplant them to the garden. Seeds need temperatures of at least 10°C to germinate properly.
However you start, when it’s time to plant outdoors, start by raking over the soil to break down any lumps.Dig down about 1 cm and plant the onion sets so that their tips are showing. Cover with soil and water to finish.
As onions swell as they grow, you need to space them about 10 and 15 cm apart and leave around 30 cm between rows.
It’s worth covering your crop in an insect-proof mesh or fleece as this will deter bird and insects from eating them!
How to nurture onions
What makes growing onions ideal for beginners is that they don’t require much care. As long as you water often and regularly remove any weeds, your onions will continue to grow.
Any onion that starts to flower has stopped growing and won’t last for long, so need to be removed and used within a few days.
As onions begin to mature, the foliage turns yellow and starts to fall over. To speed up the ripening process, either bend the tops down or stomp on them!
You can encourage the bulbs to dry by loosening the soil around them. Then when the tops are brown, pull the onions out.
Ideally, you would start to harvest in late summer before the cooler weather of autumn.
How to store fresh onions
After harvesting your onions, you first want to clip the roots and leave them to cure on dry ground for a few days, weather permitting. When moving your onions take care not to bruise as this will encourage rot to set it.
As they easily absorb moisture, onions like a cool, dry, dark and well-ventilated storage space. If the humidity is too high, they may start to sprout or rot. Avoid storing onions in plastic bags, as the poor ventilation may make them spoil quicker.
Don’t store onions with fruits such as apples or pears, as they produce ethylene gas, which will interrupt the onions’ dormancy. Also, onions may spoil the fruit’s flavour. Storing potatoes and onions closely can also ruin the potatoes’ flavour.
A pungent onion will store longer than a sweet onion. So it’s a good idea to eat the sweet varieties first and save the more pungent onions for later.
Common pests and problems
Part of successfully growing any vegetable is managing pests and diseases. And while onions are relativity hardy, both pests and disease can pose a serious threat which can be difficult to eradicate from the soil.
The best way to protect your soil is by crop rotation. Never plant onions in the same place two years in a row. Ideally don’t grow onions, garlic or leeks in the same spot for three years.
Also, when harvesting, take care to ensure that you’ve removed all traces of your onion crop. Should any be left in the ground, they may become infected over winter.
If the leaves start to wilt and brown, then the crop may be infected with onion fly. The top of the bulb may smell slightly and will begin to rot. You also might be able to spot Maggots.
Sadly, there’s no way to treat onion fly other than to dig up infected plants and burn them. However, you can cover your crop in insect-proof mesh to protect them.
Often known as Leek Rust, it affects onions, leeks, garlic and chives. Allium rust is a fungal disease which causes bright yellow spots on the leaves and can start to appear in mid to late June.
This disease thrives in humid conditions often caused by planting too many plants close together. So ensure you plant crops at a sensible distance. The only cure is to remove any infected plants and rotate crops.
You’ll first notice that they central leaves start to form a capsule near the top, which quickly flowers. The flower head will die off revealing onion seeds.
There’s nothing you can do once an onion plant has begun to bolt. You can prevent onion bolting by purchasing heat treated onion sets as they very rarely bolt.
Onion downy mildew
Resulting in poor yields, onion downy mildew is a fungal disease that damages foliage and bulbs. It’s caused by damp conditions.
It’s best to ensure the plants have plenty of light and air by correctly spacing them and by weeding regularly. If possible avoid overhead watering. You’ll want to remove any infected leaves.
That’s how to grow onions!
As you can now grow onions, there’s plenty of other veg that are just as easy to grow. Some of our favourites include radishes, carrots and sweetcorn. If you’re looking challenge, try to grow tomatoes or cabbage.