Growing Onions in Pots

Growing Onions in Pots and Containers

Onions are neither a root nor a fruit, onions are edible bulbs that can be grown in pots as seeds, sets, or transplanted to the ground.  Onions have been grown for thousands of years for at least two reasons: they store well and can be used in almost every kind of savoury recipe.  In this post, I’ll explain how to grow onions in containers at home, when to put them in containers, how long it takes for onions in pots to grow, and which variety of onions are the best for container gardening.


How to Grow Onions in Pots and Containers

Growing onions in a pot or container is quite similar to growing onions in the ground. Great-tasting onions need excellent fertilizer, healthy compost or soil, the right amount of water and sunlight as well as enough drainage to provide good results. The growing methods used to grow onions in containers are similar to those used to grow onions in the garden; the only difference is the cultivation techniques.

Spring onions can be grown in a 20-centimetre pot or bigger. Bigger, or, bulb onions are ideally grown in large containers to provide each onion with approximately 7 centimetres around each plant.

The benefits of growing onions in pots

Growing onions in containers or pots at home is an excellent option when space is at a premium. Even beginner gardeners can give it a go since growing onions in pots is relatively straightforward.

Because you’re not planting in the ground or placing the container in a garden, growing onions in pots is an excellent option if you don’t have a garden, or if you don’t have much space.  Our small backyard got very little sunshine, was all paved over but grew some amazing onions in pots for us over the years.

Our Guide to Growing Onions in Pots

What you need to grow onions in pots

All you need is a good fertilizer, healthy compost, or soil with enough drainage, water, and sunlight. Other than that, you’ll need a pot large enough to accommodate the number of onions you want to grow.   You don’t need to invest in an expensive pot or container – you can even use plastic trugs, tubs, or buckets.  But don’t forget to drill holes in the bottom, otherwise, your onions won’t drain properly and they’ll rot.

The area where you place your container will require six to seven hours of direct sunlight each day.  This is a great benefit of growing onions in containers – you can move them around to catch the sun!  If you’ve grown onions in the past in the ground, be aware that container-grown onions require more water than those grown in the ground.

The best varieties of onions to grow in pots

A wide range of onion types is available for home-growing. In terms of taste, some are best when picked early, bringing a delicate flavour to salads and stews; others benefit from remaining in the ground for longer, throughout the growing season and they can withstand cold and dry conditions. Onion types that grow well in pots and containers include the following:

Grow Globe Onions or Brown Onions

These are the regular brown onions you’ll likely see in supermarkets.  They have lovely brown skin, they’re reliable and they can grow pretty big.  You can’t go wrong growing these onions, they do, however, take up to 6 months to grow.

Electric Red Onions

If you’re new to onions, red electric onions are a fantastic choice.   These onions have a fab flavour and are also great eaten raw.  They’ll also last a long time if you store them correctly.

This is a fabulous red onion to grow that goes with this Smoked Mackerel, beetroot, and potato salad.

Shallot (Zebrune) Onions

Shallot (Zebrune) is sold in sets or individual dormant bulbs that are ready to plant when you get them.  The Zebrune is a red onion with red and white lined flesh.  It’s a mild flavour, which means it’s great in both salads and cooking.  It usually harvests earlier than other varieties of onion.

The best pots to grow onions in

When it comes to growing onions, the size of the pot makes a difference. A pot with a depth of at least 30 centimetres and a breadth proportional to its height is ideal.  I like troughs for a large number of onions, as they’re easiest grown in rows.  It’s also great to have smaller pots with different varieties, although you can mix and match.

There’s no deep root network to worry about, so they don’t need to be hugely deep.  The more space they have the bigger the onions can get.    When onions are growing, the tops of the onions should be at least 7 centimetres apart. Onion plants may reach heights of up to 1 metre, so use broad enough pots to allow the plant’s growth.  A pot that is too small will inhibit the growth of your onions.

Why grow onions in pots?

Growing onions in pots and containers is a simple and efficient way to grow your own vegetables when space is limited. At Lets Grow Cook, we’re all about making it easy to grow your own vegetables, even if you don’t have a garden.  Growing onions in pots means that you can always have an ample supply of these seriously versatile bulbs at your disposal.

Onions are a great source of vitamins and minerals – from vitamin C to B6, folic acid and fibre.  Onions help boost your immune system and regular blood sugar levels too.

Onions have the extra benefit of retaining their flavour and freshness for many months after harvest. They store well, and if you store them correctly, then you’ll get the same flavour and taste months later. Onions are simple and easy to grow vegetables.  What’s also great about growing onions is that all varieties pretty much grow the same way, so there are no special techniques to learn.

With most homegrown foods, the better taste tends to come from eating it fresh, but with onions, so long as you store them correctly that flavour will be retained for months

When to plant onions in pots

Onions are typically planted in the spring, between March to late June. Some varieties may be grown from October to mid-March since they are less susceptible to cold, which would typically induce bolting. If the weather is frigid, start your onions indoors or in a greenhouse and move them outdoors when the weather warms up.

During the first stages of growth, onions need cold temperatures.  You can grow onions from seed by sowing between March and June. It is common for onion bulbs to form as the temperature rises and onion tops to start developing when the temperature falls.

You can sow onion seeds four to six weeks before the typical last frost date – or even earlier if growing them indoors. You can harden off indoor seedlings when they are 5-7 centimetres tall by exposing them to above-freezing night temperatures.

A quicker way to go from start to finish in growing onions in pots is to buy onion sets.   These are small onion bulbs that were grown from seed last season.  They are the EASIEST way to grow onions in pots.

You’ll be able to buy onion sets in early spring and late summer online (try these here ) and from garden centres.  Plant onion sets from mid-March to mid-April.  You’ll find some onion varieties – like these ones which are suitable for planting from October to mid-March.

Where to grow onions

Given that onions don’t need a lot of space, growing them in pots is a great option.  When growing onions in a tub or pots, the container must be put in a location where it will get six to seven hours of light every day.   Your location needs to be sheltered and if you’re growing onions in a pot, then you’ll want to start things off after the risk of frost has passed. 

If you’re growing onions inside and don’t have access to adequate sunlight, placing fluorescent bulbs or grow lights near the onions may help to supplement the light.

How to plant onions in a pot

Start your onion seeds indoors eight weeks before you want to plant them in the pot. If you’re using onion sets, plant from mid-March to mid-April

In a container with holes for drainage, sow the seeds 2-3 centimetres deep, and space them 4-6 centimetres apart.  If you’re using sets, then plant them to the same depth.

Keep adding compost to the roots as they expand. For best results, add some vegetable feed (I love using tomato feed) when onion tops are approximately 15 centimetres high. This trough is a great option for growing onions in.

How to grow onions from seed in a pot

Growing onions in a container from seed is easy. Make three or four drainage holes at the bottom of the plastic container, each 1 centimetre apart. Make two wide ventilation holes on the sides as well. Fill the container with 7 centimetres of compost.

Sprinkle the onion seeds over the soil, spacing them approximately about half a centimetre apart, you’re likely going to discard the weaker seedlings later.  Cover the seeds with compost and water then with a fine spray. After the seeds have been sown, pop this nursey container in a bright location, but make sure the temperature isn’t going to fall below 15 degrees.

Growing onions in pots sets in trays

Keep the compost damp, but not soggy.    You can start this off inside in January if you have space and your onions will be ready for transplanting outside in April.   When you transplant seedlings you’ll want to space them out – about 10-15 centimetres apart.  And you’ll want to harden them off slowly before truly transporting them outside.  SO taking them outside on pleasant days for a little longer each time is the best way to do this. 

How to grow onion sets in a pot

Growing onions from sets in a pot couldn’t be easier.  Buy your sets (check these out as a great option), press them gently into your container, so that the tip is only just showing.  Firm up the compost around them and water the container well.  Onions are easy to grow in containers because they don’t have an extensive root base – but that also means that they’ll benefit from some good compost (check out our recommended compost for vegetables here).    You may also want to look at a good fertilizer.  We recommend this for growing onions.

onion sets for planting

Watering and Feeding Onions

Onions aren’t particularly thirsty, but onions grown in pots will need more water than those grown in the ground.  They do NOT like being overwatered.  So if you get some heavy weather you’ll want to try and ensure that your pots are draining and perhaps move them to a covered area.  Onions do well with a regular supply of nutrients, but you don’t need to give them a huge amount – you’ll likely end up with loads more foliage and possibly flowers if you overfeed them.  I’d recommend using a good general vegetable fertilizer (like this one ) perhaps once a month, but to be honest, if they’re looking healthy just leave them.

When the onions are well-formed – you’ll see them peeking at the surface of the compost or soil, then stop watering and feeding, as contrary to what you might think this will actually encourage them to focus on developing the bulb.

Harvesting Onions

The time to harvest your onions depends on the variety, the weather and what the season has been like.  If you’ve sown in spring, then your onions will be ready in later summer or early autumn.   When they’re ready to harvest, the onion leaves will droop, they’ll turn yellowy and then brown when they’ve stopped growing altogether.

harvesting onions

Loosen the soil with a hand fork and lift the onions out.  If you’re going to store them then they need to dry properly for a few weeks otherwise they’ll go mouldy.  Dry them in a cool, dry airy place – a greenhouse or shed is great.  This drying process is called curing.  The outer skin will go dry and papery, which actually protects the inner onion.  When they’re “cured” cut off the extra top leaves and foliage and store them.

How to store onions

Keep your onions (including red, yellow, and white varieties, as well as shallots) dry – preferably organic material bag to minimize mould and sprouting, and store them in a cool dry place. I don’t recommend plastic, but cotton or natural fabric is good.  A hessian sack is great, a paper bag is good, a basket is also good.  You can also store onions in a wire basket. 

It’s imperative to keep your onions out of direct sunshine and in a cool, but not freezing, environment with some breeze, rather than in direct sunlight. Store them in an onion bin or crate in the pantry, garage or cellar.  When stored in a cool, dry, dark location, they can last for up to twelve months.

storing onions in a sack

Dealing with pests and problems when growing onions

There are two types of rot that you may encounter when growing onions.   Onion neck rot occurs when the soil or compost is too damp.   You’ll notice this as a grey fungus that’s a little fluffy around the neck of the onion.  It softens the flesh of the onion, which turns transparent and dries out.  Keep your soil well-drained to avoid this.  White rot is a white fungal growth that is present around the roots and bottom of the onion bulb.  You can’t fix this one.  Dig them up, burn them and don’t plant anything in the compost that you’ve dug them up from.

If you grow your onions in large pots or tubs, weeds may sprout and compete with the onion plants. Remove them as soon as possible by pulling them out with your own hands – check out our guide to gardening gloves to protect your hands

FAQ’s on Growing Onions in Pots and Containers

Got questions about growing onions in pots? Or want to know more about growing onions in containers, and we haven’t answered your questions? Check out our frequently asked questions about growing onions in containers below, or ask us yours in the comments.

Can you grow healthy onions in pots?

Most definitely. Onions are one of the most adaptable crops for container gardening. They may be grown both inside and outdoors, and since their roots do not stretch too far looking for nutrients, they need a minimal growing area. Growing onions in pots and then transplanting them into the ground also works. However, growing onions in containers in the UK just means that it’s simpler to move the whole pot about the garden as your garden and weather conditions change.

How deep should a container be for growing onions?

When determining how to plant onions, make certainly sure that you plant them at the proper depth. Enough onions will be planted in an area at least 25 centimetres deep but at least one meter wide.

How many onions will one onion grow?

Each onion plant produces one onion. The potato onion, also known as the multiplier onion, is a kind of onion that develops roughly 5 onions per plant. The potato onion, formally known as Allium cepa var. aggregatum, is linked to shallots and garlic more closely than other onions.

Can I grow onions from the supermarket?

Yes, you can grow onions from the grocery store, but you shouldn’t. They will grow if you plant them. However, if it’s already a bulb, the next great growth surge will be to develop a seed stalk. The bulb will stop growing and shrink and finally vanish into the stalk’s base. 

Should I grow onions from sets or seeds?

Onions are a versatile vegetable that is used in various dishes, and growing your own ensures you’ll always have them on hand. They are simple to develop from immature bulbs known as sets. Although the seed is available, growing them in sets is the most convenient and time-efficient method and you know we like the easy option here at Let’s Grow Cook!

How long does it take to grow onions?

Onions are a cool-season crop that takes 90 days or more to grow onions in pots. Because of the extended growing season needed and their preference for colder conditions, sowing onion seeds immediately into the garden in the spring makes it difficult for the bulbs to mature before the arrival of warm temperatures.

Final Words on How to Grow Onions in Containers

You won’t save much money by growing your own onions, they are likely to be cheaper buying them in bulk in the supermarket, so why grow your own onions?  Well, the taste.  It’s definitely better.  The variety is also much better.  If you normally only buy globe onions, try growing shallots (which can be a lot cheaper to grow your own than buying), or some heritage varieties.  My goal of growing my own onions in pots is for the sake of taste.  And so, I hope you found my guide on how to grow onions in a pot helpful.  See how it works if you try growing your own onions in containers. Once you tried it, you’ll never go back to store-bought onions again!

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