Onion sets…everything you need to know

Where would we be without onions? They form the basis of so many meals on almost a daily basis. A true kitchen staple.

You can grow onions from seed or from set. Sets are one of the most popular methods of growing onions. This article explains everything you need to know about onion sets.

What Are Onion Sets?

Onion sets are small, immature onions that have been grown from seed during the previous season. They are harvested whilst the bulbs are small, usually when they are around the size of a marble. They are stored in a dormant state ready for you to re-plant the following season. Onion sets are usually sold for either spring planting or autumn planting with some varieties such as our onion ‘radar’ more suited to autumn planting. Sets for autumn planting tend to be Japanese varieties.

Deciding whether to grow from seed or set is often just down to your own personal preference. Sets are easier to grow into full sized onions as they don’t take too much effort to plant. Their larger size makes them much easier to handle than a small seedling or a handful of seeds. Sets don’t require thinning either. You can plant them at the correct spacing to allow them to mature into full sized onion bulbs.

Why Use Onion Sets?

Autumn sown sets will usually be ready to harvest around 6 weeks before spring sown sets and much earlier than onions grown from seed. Autumn sets develop strong root systems over winter so that they are ready to put on growth immediately as soon as the warmer temperatures arrive and the days start to get longer. An added benefit of autumn planted sets is that they help you to start getting ahead at the quietest time of year!  If you want to have a year-round supply of onions then sets may be your secret weapon!

What should I look for in an onion set?

Firstly, the variety should be suitable for the season you are planting in. If you use a spring sowing variety in the autumn then the cold temperatures are likely to cause the onion to flower before it is ready. Conversely, Japanese varieties are not sensitive to the cold in the same way.Autumn sown varieties are therefore a great addition to your planting plan if you want an earlier harvest and have plans for year-round onions!

Secondly, size matters. Bigger is not better when it comes to onion sets. Larger bulbs are actually more likely to stop growing and to send up a flower shoot earlier. If you want to harvest bigger onions, plant the smaller sets!

How to plant onion sets

Planting onion sets is super simple, simply plant direct into the ground, about 2cm deep and with the pointed end at the top! Space the bulbs around 5-10cm apart and leave a 20-30cm gap between rows to allow enough space for weeding.

You can also plant your sets into raised planters or large pots.

If your soil is particularly wet you can even plant your sets into large modules to start them off. This can be particularly useful for autumn plantings to avoid the bulbs sitting in wet soil all winter where they are likely to rot.

How do I know when my onions are ready?

Whether you are growing for green onions or for larger bulbs, you can harvest the onions at any point that is preferable for you. If you are growing onions for storage, you shouldn’t harvest until they are fully mature. You will know when they are ready as the leaves will start to die back, turn brown and flop over. You can then start the curing process.

What is curing?

Curing is the process of making sure the outer layers are completely dry so that they can be stored. You should cure your onions undercover and make sure the air can circulate around them to prevent mould or rotting. It will take a couple of weeks for the skin to turn papery enough and for the leaves to shrivel up but once this happens you can start trim off the roots and plait your onions ready for storage. Always store your onions in a cool, dry, well-ventilated place out of direct sunlight and check your bulbs regularly for signs of rotting.