How to Grow and Harvest Onions

Onions are a staple ingredient in most culinary cultures around the world. In my household, I tend to go through a lot of onions per week including spring onions, leeks and other types of alliums out there. I pickle them, make chutneys and use onions in a huge variety of dishes.

In my garden, I decided to grow the most common onions and picked at least one of each variety. This post will focus on how to grow the common red and yellow onion to get the most out of your plants.   By that, I mean a solid, great tasting onion that can store for 4-5 months over winter before we get our first spring onions started again in the garden. So here is my guide on how to grow and harvest onions and spring onions.

Preparing the planting area

Onions like fertile, well-drained soil that has not had fresh manure on it in at least one season. I rotate my crops so that the onions go where some of the heavier feeders like tomato or beans were the previous season. That way you get them into a space that is well fertilised but also not prone to be carrying any disease that onions are prone to if they are grown in the same space every year. The place you are planting your onions in needs to have at least part of the day in the sun to properly form bulbs, so a south or west facing bed will give you the best results. To improve the drainage of the soil, it would be a good idea to dig in some sand, grit and other material that will aerate your soil.

Bear in mind that we live in Hampshire, southern England. For us south facing spots seem to work the best, but you might have to adjust it depending on your location.

Planting:

If you are using sets of smaller onions to plant out, you can do this during March or April and have a good crop in a relatively short time. If you are sowing seeds, these will need to be started around Christmas time and planted out at the same time as you would do it with the sets. Unless you are very confident at sowing seeds or want a special variety, I would go for the sets. We usually do as you can see above.

Plant the sets or seedlings in rows based on what you are going to use the onions for. If you are going to use them as spring onions, you will not need such a great distance between each plant – meaning that you can save a lot of space by having an area for spring onions and an area for the onions that you want to go to a bulb. As a rule of thumb, onions should be planted 10-12 cm’s (5 inches) apart if they are going to become bulbs. You can halve this distance if you are going to grow spring onions, in fact, your spring onions will be best if they are a bit cramped. 

The trick in this method lies in harvesting every second onion and use it as spring onion while leaving the other half of the crop in the soil to fully develop into a nice bulb.

Harvesting

To harvest onions that have been left to form bulbs, it is important that they get about two weeks to dry off. There used to be a tip that said that you should knock the growth of onions over once their bulbs have swollen, but this has been debunked. The most important thing to do is to make sure you dig any soil away from the top of the bulbs so that they can start hardening off. The leaves will indicate to you when they are ready for this by starting to fade. If you follow these steps, you will get onions that will store for much longer. Breaking the neck of the onion will only lead to it rotting more easily if you live in areas with regular rainfall. For spring onions grown from seed all you need to do is to keep picking and re-sowing, that way you have a continuous harvest.

The last tip that I can give you is to chop any onions that look a bit scruffy or small and freezing them straight away. Frozen onions are great for dishes that require chopped onions. This way you are guaranteed that you will not waste any of your homegrown vegetables. I hope you enjoyed my guide on how to grow and harvest onions - please let me know how yours are doing if you grow any yourself.