Onions are usually planted in spring as bulbs. They are usually ready to harvest in late summer / autumn.
You can either harvest your onions when they reach your desired size or you can let them grow until the plant stops growing.
Some years your onions will grow very well and they may end up too large to be convenient for you to use if you let them continue to grow. If this is the case you will need to dig them out of the ground with a garden fork, shake all the soil off them and let them dry in the sun for a week before storing them.
If your onions are nearly finished growing for the year and will not be too large you can let them grow on until they finish growing before harvesting.
How Do You Know When Onions Are Ready For Harvest?
An onion plant will show when it has finished growing and is ready for harvest when its leaves start to turn brown at the edges and they flop over rather than standing green, upright and tall.
How To Harvest Onions In Wet Weather
It can be difficult to guarantee a couple of weeks of sunny weather at harvest time. If this is the case you can bring the onions under a roof – into a greenhouse, polytunnel, or a shed – which has a good flow of air through it. Set them up on wire racks or place them in slatted wooden boxes and let the curing process begin.
How Do I Cure Onions After Harvesting?
Curing onions is when you remove moisture from the outermost layer to act as a barrier or protection for long-term storage. This drying of the outer skin will reduce infection, mould or rot coming into the onion and help to prevent moisture escaping which would result in a spongy soft onion.
The more you can spread the onions out the faster they will dry. The onions will be ready to store when the skins are dry, crisp, and brittle. The leaves should be completely shriveled up and the roots will be dry and hard.
How to Store Onions Long Term
Onions like to be stored somewhere dry, dark, and cool with good ventilation. Heat and still air encourage mould growth. If you had to choose between an unheated room in the house vs a shed outside, the shed will be better because it will probably be easier to have a draft blowing through it.
You should place your onions into net bags or slatted boxes for storage and use up any onions which appear to have not cured so well (soft onions) or still have thick fleshy necks. The onions will store for around 6 months easily if you get the conditions right.