Last Updated on 09/10/2023 by Barney
Onions are easy to grow, making them a great choice for novice gardeners. In this article, I will discuss the 5 steps for planting & growing onions. Whether you are an experienced gardener or just starting out, these tips will help you produce delicious onions of your own!
As a professional gardener and keen vegetable grower it is a great joy to share my experience in growing vegetables. Nothing is better than watching something grow and harvest to eat when ready. Once bitten you’ll be forever smitten when eating your own fresh onions.
I promised you easy steps. For this guide I will be discussing planting onion sets. This method is the easiest, most common way amongst vegetable gardeners. For those wanting to delve deeper I shall post a separate piece on how to grow onions from seed.
Now, lets go and plant some onion sets… ….
Before continuing choose the Season to Plant Onion Sets
There are 2 times of the year in the UK when onion sets are available. These are for Autumn Planting & Spring Planting.
Typically, planting Autumn onion sets will provide you with a harvest around late Spring. With Spring planted onion sets you can expect a later harvest , from early to late Autumn.
The best time is to plant Spring sets is in early spring , mid March to mid April. When planting Autumn sets the season for planting is September through to the middle of November.
When stored correctly onions can keep for a year so planting at both of these times will guarantee you’ll never be short of onions.
Step 1. Onion needs & Soil Preparation
Onions thrive in full sun planted in a nutrient rich, water retentive & loose soil. For your onion plants to thrive do not skip on preparing the planting bed. Fertile soil is the elixir of life when it comes to successful onion growing.
Soil Preparation
Firstly remove all weeds and debris from the growing area and give the soil a covering of peat free compost, well rotted organic matter or well rotted manure to around 2cm in depth. . Add to this a sprinkling of slow release fertiliser such as Vitax Q4 and work into the soil with a garden fork.
Adding well rotted organic matter will improved soil structure & drainage. It also holds onto moisture, especially important in dry spells.
Onions are hungry plants. Adding Vitax Q4 before planting the sets provides the nutrients needed to get the sets off to a great start.
Once complete rake the soil surface to a flat level. The texture your a aiming for is a loose soil. This makes planting the sets an easy process.
Time spent on soil preparation is key to healthy onions. The ideal soil texture for planting onions is one that very loose, one that you can easily push your finger into.
On clay & heavy soils consider planting onions in ridges or raised garden beds. This will keep the onion roots from being sat in permanently wet soil (which leads to rotting)
Step 2. Choosing & Buying Onion Sets for success
When buying onion sets always ensure the sets are certified and disease free. Look for labelling when purchasing from a garden centre.
Onion bulbs can be prone to bolting (flowering) which you want to avoid as it stops the onion bulbs from completing the journey into a gorgeous, swollen, sweet onion bulb .
When choosing the onion crops to plant look out for varieties that have proven a good resistance to bolting or have been heat treated.
Popular UK Spring planted onions are:
Sturon
Caramel-coloured onions with hints of red, these traditional yellow onions are a must for any self-respecting gardener. With a plump, semi-rounded shape, they’re just the right size for slipping into stews and casseroles. And with an RHS AGM award to their name, you can be sure that they pack a flavourful punch. Plant in March for harvesting in August.
Hercules
Hercules onions are a great choice for gardeners who want to try their hand at growing onions for shows. Known for its strong flavour with almost perfectly rounded bulbs. They crop earlier than most spring-planted sets, with harvesting taking place in June or early July. Hercules onions are also popular among vegetable show growers because they tend to do well in competitions. If you’re looking for an onion that will give you a good yield and that has a strong flavour, Hercules is a great option to consider.
Stuttgarter Giant
Stuttgarter is an old favourite amongst vegetable growers due to its reliability. It produces sweet, semi flat bulbs that are excellent for cropping and storing. The variety is very tolerant to both heat and cold, making it a great choice for growers in all parts of the country. Additionally, Stuttgarter is shows excellent resistance to common onion diseases . With its excellent flavour and storage qualities, Stuttgarter is a great choice for anyone looking to add a delicious and versatile vegetable to their garden.
Hyred (red onion)
The Hyred is a delicious red onion that shows a good resistance to bolting. The bulbs are crimson red and a semi globe shape. Harvest in early September. Stores well into early Spring . This type of onion is perfect for those who enjoy the flavour of onions but don’t want them to be too overpowering. The Hyred is also a great addition to salads or as a garnish on cooked dishes. If you’re looking for a tasty and versatile onion, the Hyred is a great choice.
Popular UK Autumn planted onions are:
Electric (red)
If you’re looking for a unique and eye-catching onion, electric red is a great option. Electric is characterized by a deep red skin and crisp, white flesh.
Electric red onions are also relatively large, making them perfect for slicing, using in salads or as toppings on burgers and sandwiches.
Shakespeare
characterized by their large size and strong flavor. Shakespeare onions commonly used for cooking, as their strong flavor can add a lot of depth to dishes. They are also a popular choice for pickling, as their flavor mellows out nicely when preserved in vinegar.
Whether you’re looking to add some zest to your cooking or simply want to enjoy a delicious pickled onion, Shakespeare onions are a great option.
Senshyu
Senhyu onions commonly grown in Senshu, Japan. Known for its strong flavour and high quality. Senshyu onions are typically larger than other types of onions, and they have a deep purple color. In addition, Senshyu onions have a high sugar content, which makes them sweeter than other onions.
Often used in Japanese cooking, and they are also popular in other Asian countries. If you are looking for a high-quality onion with a strong flavor, then Senshyu onions are a great option.
Autumn Champion
Particularly suited for Autumn planting. They are large, round onions that have a deep golden-brown skin. The flesh of the autumn champion onion is white and crisp, with a mild flavor. These onions are easy to grow and store well, making them a good choice for autumn planting. Thanks to their large size and deep color, autumn champion onions also make a good choice for pickling or canning. If you’re looking for an autumn onion that is easy to grow and has good storage qualities, the autumn champion onion is a great option.
There are many other onion varieties available. Spend some-time researching the right varieties for your taste buds. I have had good success buying sets from Suttons & D.T.Brown.
Step 3. Planting the Sets (the exciting bit)
Most varieties of onions (except Spring Onions) are planted with the same method. The only difference will be the spacing between them. ie small onion varieties need a smaller space between planted sets than larger onions.
To plant onion sets as follows:
- Position sets on the soil surface where you wish to plant them. If planting in a row I find a taught string line between a couple of bamboo stakes helps.
- Use a dibber, your finger or trowel to mark a hole in the soil. Large enough for the set to drop in to. Remember, it is important that the top of the onion is still visible. They will still grow shoots if planted too deep but unlikely to develop a bulb.
- Firm in with your finger
- Water well, wait watch the magic happen
That’s it. That’s all there is to do to plant onions.
Step 4. Care for the growing Onions
Onions are the ideal crop for the time crunched grower. Just a bit of TLC during the growing season and you should be harvesting show stopping onions.
Looking after your planted onions is key to getting a good crop, and there are a few things you need to do.
- Water onions during dry spells. Be mindful of overwatering. Over-wintering onions do not require watering.
- Stop watering once the bulbs have swollen, this is around mid-summer time.
- They also benefit from a feed every few weeks, using a general-purpose liquid fertilizer. I use an organic Seaweed version as I like my homegrown crops to be as organic as possible.
- Give over-wintering crops a nitrogen-rich late winter feed such as pelleted chicken manure or Sulphate of Ammonia. An application of a late winter feed will wake them from winter slumber and kick start growth.
- Onions hate competition from weeds. Keep the space between rows and
Step 5. Harvesting, Curing & Storing Onions for a later day (the even more exciting bit)
For Autumn planted onions the time to harvest is usually in June. For Spring planted onions it is usually around September-October . The weather and the soil type will also affect when your onions are ready to harvest. When the weather has been dry the onions may need a little longer. In very wet weather they are potentially ready earlier.
The secret to harvest onions successfully is to pick a window where there will be sunny weather for a few days as once gently teased from the ground they need to be spread out on the ground to dry.
The leaves of the onion will start to yellow and fall over when they are ready. To harvest, loosen the soil with a fork and lift the onions carefully so as not to damage them.
Once you have harvested your onions, it is important to cure them before storing. This helps to prevent mould and makes them last longer.
To cure onions, lay them out in a single layer on a mesh or wire rack in a cool, dark and dry place. Leave them for two weeks to allow the skin to harden. Once the onions are cured, trim the roots and leaves leaving about an inch of stem. Store your onions in a cool, dark and dry place. A mesh bag hung in the shed or garage is ideal.
Planting Sets vs Growing from Onion Seed
There are some advantages in growing onions from seed but I think they are outweighed by the disadvantages especially when it might be the first time growing onions.
Spring sown onion seeds will not have enough time in the growing season to produce large bulbs. They will produce edible immature bulbs but never reaching the bulbs fulls potential.
If you plant onion seeds they are going to need more attention than sets, especially in the early stages of growth where watering and weeding will have to be closely monitored.
however being a biennial crop they have little chance of bolting (flowering) in the first year.
Sets however are 1 year old onions. Whilst there is a chance of ‘bolting’ these will produce bigger onions and do not require the space and equipment growing from seed involves.
Tips to avoid Avoid bolting
Bolting is a term used when a vegetable produces flowers.
Stress is the main trigger for bolting, onions are no different. The main types of stress that can cause an onion to bolt are:
– Temperature: both too hot and too cold can induce bolting
– Water: Onions need a consistent supply of moisture, if they dry out totally or are waterlogged they can bolt
– Nutrients: onions need a good supply of nitrogen to produce leaves, if they are deficient in this they will bolt in an attempt to produce seed
There are a few things you can do to avoid bolting:
– Choose the right variety: some onions are more resistant to bolting than others. This will be displayed on the packet when buying from a garden centre or displayed from your supplier on-line.
– Sow at the right time: Sow onion seed when the weather is cool, if you sow them too early they could bolt before they have a chance to mature
– Transplant carefully: if growing onions from seed don’t like being disturbed so transplant them carefully and make sure they have enough space to grow
The bad news flowering leads to the vegetable halting its growth with the energy going in to produce seed thus producing an immature bulb. All is not lost. Eat them first as they do not store well.
By following these steps you should be able to grow onions that taste great and resist bolting. Try different varieties and methods and see what works best
Common Onion Pests and diseases
Onion Maggots
I know right, sounds disgusting.
Onion flies are responsible for these unwanted pests. The adult onion fly lays its eggs which then pupate into maggots, attacking the base on your prized onions.
Usually, this is not a problem when growing from sets, it’s more of a problem if you grow onions from seed.
I have never experienced this problem but for peace of mind cover your crops with an insect mesh and always use well rotten organic matter.
Pigeons
Yup, as well as uprooting garlic sets pigeons also enjoy up-rooting onion sets. This is not a problem when the onions have put down roots. For protection in the early stages cover newly planted sets with a mesh crop cover.
Onion Rust
Identified by brown & orange raised markings on onion leaves. Its cause is a fungus that affects most of the allium family of vegetables. This fungus thrives in damp & humid conditions
When plants become infected the bulbs will stop growing rendering them pretty useless. There are steps you can take to mitigate the risk of getting onion rust.
- Plant sets in full sun
- Do not overfeed – over feeding with Nitrogen is a known culprit
- Promote good airflow by planting at recommended distances
That’s Wrap from Me
Now that you know everything there is to know about growing and harvesting onions from onion sets, go ahead and get started on your own delicious crop.
Be sure to follow the guidelines I’ve set out in order to ensure a bountiful harvest of delicious home grown onions. If you have any questions or run into any problems along the way, don’t hesitate to reach out for advice. With a little bit of planning you could be enjoying homegrown onions all year!
