How To Grow Onion Sets In Containers In Spring – Step By Step Beginner Guide

Discover How to Grow Onion Sets in Containers in Spring

In this blog I am going to discuss how to grow onion sets in containers in spring. This method is a simple and effective way to grow your own vegetables when space is limited.

If you have a city garden or backyard, you may not have much room to grow more ambitious vegetables or to keep a greenhouse – so onions are a great option for those in urban areas!

Personally, onion sets are a favourite of mine because they are relatively easy to grow. You also tend to see shoots within a couple of weeks – which is heartening for beginners who may not be sure what to expect when first starting out growing vegetables.

To successfully grow onion sets in containers in spring, you will need to pick the best container for your onions, use mixed purpose compost or potting soil for planting and keep them in a sunny spot and regularly water and regularly fertilise your sets.

In this article, I’ll start by looking at why growing onion sets in containers in spring is a good idea and then explain how to plant your onions step-by-step!

Table of Contents

Why Grow Onion Sets?

Onions have been grown for thousands of years because they store well and can be used in many different savoury recipes. Onions are an excellent addition to your container vegetable garden!

So, by growing your onion sets in spring, you can have an ample supply of these versatile bulbs at your disposal. And you can grow onion set all year-round (although the best time is early spring).

The key advantage of an onion set over a seed is that when you plant one, it is at a more advanced stage of growth so the planting cycle is shorter.

And, onion sets are also easy to purchase – almost every gardening centre stocks them along with some local stores. They are less complicated to grow than seeds because there are fewer varieties and they are less likely to be affected by disease.

How to Grow Onion Sets in Containers – Step-by-Step

To get started growing onions in containers, you will need onion sets, containers, multi-purpose compost, and fertiliser – here’s a quick breakdown:

Onion Sets

For sets, I advise planting sturon onion sets, which are yellow onions – the most commonly used type of onions.

I tend to purchase 50 sets, so I have some left over to plant onion sets indoors after filling up my outside containers. Starting off onion sets indoors is best done in February, so you can then move them outside once they start to grow.

Sturon sets have a strong flavour and produce high-quality, medium-sized bulbs that grow to a height of 30 cm and are relaxed and stress-free to grow. And, they work well as a base for many curries and sauces – and of course onion soup.

If you plant them from February to May (springtime in the UK), fingers crossed you should be able to harvest them in late summer or early autumn. Remember that the date of harvest largely depends on the type of climate you have.

Containers

Many people believe that because they have limited outside space, it isn’t possible to grow vegetables like onions. But, growing onions in a container or pot is quite similar to growing onions in the ground.

The depth of the container is important because, although there is no deep root network to worry about, the more space there is, the bigger the onions can get.

So preferably, you want a container with at least eight inches of depth. Troughs are also great for growing a larger number of onions as sets are easy to grow in rows, although you can use smaller pots if you feel that works best.

In the video above, I used a long, recycled plastic, trough – 36 inches in length by eight inches deep. I also use pots from my local hardware store for planting onion and garlic sets which are usually made from terracotta and around 13 inches wide by ten inches deep.

When planting in containers, you need to ensure that there is some kind of drainage because otherwise, the soil will get clogged up. Unfortunately, containers don’t always come with holes, so you may have to make them yourself or ask the person you’re buying your containers from to drill them in.

Soil

For growing onion sets in containers, you will need to use soil that is light and drains well. I advise using Premium Miraclegro all-purpose mixed compost (20L).

Make sure you go for the 20 litre option because you’ll be surprised how quickly you can run out of soil. You can also use potting soil – and for fertiliser try Doff Bonemeal plant food.

Pro Tip: Make sure you allocate some space to store your compost, as it can be heavy and bulky.

Growing Onion Sets Step-by-Step

Now that you have your onion sets, container and soil, it’s time to plant your sets.

Start by filling up the container with your mixed compost and then push your onion sets around 6 cm below the surface. Make sure you cover them up with substantial soil to protect from rain (a must if you’re living in the UK or other rainy climates).

I usually leave around 15 cm between each set and plant around six onion sets in my trough, along with about three in my terracotta pots.

I keep my containers in a sunny spot and water regularly. For fertiliser, I use my slow-release plant food around the roots from a month or so after planting.

Before you harvest your onions, you may want to move them to a bigger pot. Make sure that you check for the key signs they’re ready to transplant before you move them over.

How do You Know when Onion Sets are Ready to Harvest?

The signs that your onion sets are ready to harvest is when their foliage turns yellow and stems droop. It’s important to choose a sunny day for harvesting so that the onions can dry out, which is necessary for long-term storage.

Unfortunately, weather patterns can be unpredictable and challenging to navigate – but if you plant your onion sets in spring they should be ready to harvest around August.

But, the reality is that scorching heat, strong winds, and continuous rain in the late summer/autumn season can also impact the quality of onions and their long-term storage potential.

So, keep posted on your local weather conditions and adjust the harvest time accordingly to ensure the best possible outcome.

Sometimes onions can show all the outward signs of being ready to harvest, yet the bulbs can still be quite small (see the above picture).

So, it’s important to test by harvesting one and it will give you a good understanding of the development of the rest of the bulbs. If the bulbs are still quite small, you may want to leave them a bit longer.

How to Grow Onion Sets in Containers: Final Thoughts

To conclude, growing onions in containers is a fun and easy way to get started with vegetable gardening, and doesn’t require much space or maintenance.

Onion sets are an excellent option because they are cheap, easy to purchase and there are less varieties on offer so they are simpler to grow than seeds.

When it comes to harvesting, proceed with caution and keep in mind local weather conditions.

If you keep the above in mind, you’re likely to be successful in your onion growing mission – but if not, there’s always next year!

Plus, you get to enjoy the satisfaction of growing your own food and using it in your recipes. So why not give it a try?