Greenhouse, Garden & Allotment Blog

Growing Onions

Posted by Alix Francis on 9th Jan 2019

One of the easiest crops to grow and the most featured ingredient in recipes around the world. Onions are usually grown from baby onions which are called ‘sets’ however onion seeds are available.

If you want a quick, easy crop of onions, starting from sets is the route to go.

Growing Onions from Sets

Before sowing your onion sets it would be beneficial to improve the soil with either a bucket of compost or well-rotted manure.

To get your onions to thrive you need to sow them in a sunny, sheltered site with fertile, moisture-retentive soil.

Rake over your soil to break down large lumps and begin to gently push your onion sets into your soft, well-worked soil with their tips slightly showing. Firm the soil around them once sown.

Aim to sow each set 5-10cm apart in rows of 25-30cm.

Cover your sets with a fleece or netting until the roots are established to stop birds lifting them.

Although onions are better suited to growing in open areas, they can be grown in short rows in large, deep containers or raised beds.

Unfortunately, onions aren't suitable to be grown in grow bags.

Tending Onions

During dry spells, water your onions well as they thrive in moisture rich soils but don't over water.

Applying a nitrogen rich fertiliser in the spring to autumn planted bulbs gives them a boost.

Always hand weed onions as they are shallowing rooting and might be torn out when using a hoe.

Common Problems

Onion White Rot

A Soil-borne fungus that will cause yellowing and wilting to the foliage above the ground, whilst beneath the soil the roots will be rotting. A fluffy white fungus will appear on the base of the bulbs that later become covered in small, round black structures.

Symptoms are yellow, wilting foliage.

The Cure/Remedy

Currently there is no chemical cure for onion white rot when it is in the soil.

Onion white rot can be transported in the soil so it’s important not to introduce it to clean sites. Keep tools and muddy footwear clean too to stop the spreading of the disease.

Leek Rust

A fungal disease which causes bright yellow spot on the leaves. Often common during long, wet spells.

Symptoms are bright orange pustules on leaves.

The Cure/Remedy

Once your crops have the infection there is currently no cure. Leek rust can be avoided by not crowding plants.

Crowding plants increases humidity which is likely to spread infection.

Any affected plant material should be disposed of and be sure not to grow any onions, garlic or leeks in that area for at least 3 years.

Mild leek rust attacks shouldn’t harm the plants but serious infection will cause the leaves to shrivel and affect yield.

Onion Downy Mildew

A fungal disease that damages foliage and bulbs typically present in damp conditions.

Symptoms are yellowing leaves and dieback with white and then purple fungal growth.

The Cure/Remedy

Keep plenty of light and air around the plants by sowing them with the correct amount of spacing between them.

Make sure you stay on top of weeding and avoid over watering your crops.

Infected leaves can simply be removed.

Harvesting Onions

When the foliage starts turning yellow and toppling over, onions can be harvested.

Lift your bulbs before the foliage completely dies down.

Dry your onions by laying them out on a rack that will get full sun outdoors or in a well-ventilated greenhouse for about two weeks to ripen or you can dry by spreading and laying them out on a newspaper indoors to dry and ripen.

You will know when they are dry because their foliage becomes dry and papery.

How to Store Onions

Hang or string your onions in nets in cool, dark, dry places.

If stored correctly they should last for months.

Onion Varieties

  • Setton - Easy to store and peel with a strong, sweet flavour to them
  • Hercules AGM – Produces quality crops of large onions with a robust flavour
  • Red Baron – Stores well over winter and has a nice, sweet flavour
  • Ishikura - A mild tasting bunching onion that tastes great in salads, soups or even fried
  • Sturon AGM – Medium sized bulbs that store well over winter. A reliable onion with excellent flavour

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Email us - hello@norfolk-greenhouses.co.uk
Call us - 020 3011 2040

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