Growing Onions: Top Tips On How To Grow Bigger Onions | Polytunnel Gardening (2023)

Sean Barker

Onions are a very versatile vegetable and can be used in many food products, and you can easily grow them yourself if you are an onion lover. In this article, we will look through how you can effectively grow onions in your garden in simple and quick ways.

Growing Onions: The Complete How-To

Find a set of immature bulbs and choose what season of the year you want to plant and grow them in. Onions can be grown between early autumn and are commonly grown in spring to give them ample time to grow and be harvested in the summer.

We will cover the following topics about growing onions:

Table of contents

What Are the Best Conditions for Growing Onions?

How to Plant Onions

How To Care for Growing Onions

(Video) 6 GENIUS Tips To Grow The BIGGEST Onions EVER!

How To Harvest Onions

How Do I Get My Onions to Grow Bigger?

Grow an Enormous Onion Batch

What Are the Best Conditions for Growing Onions?

Onions are best grown in sunny, open spaces with good quality, well-drained soil. They also need either compost or well-rotted manure to get appropriate organic matter for correct growth. Wet soil tends to weight down on onions, so growing them on raised beds will help ti improve their drainage too.

Also, be sure to choose what variety of onions you would like to grow. They are divided into three categories: long-day, short-day, and immediate-day type onions.

Long Day: These will form bulbs when they receive about 14 hours of sunlight per day, hence why they should be planted and grown during the summer.

Short-Day: This type of onion needs 10-12 hours of sunlight to begin producing bulbs.

Immediate Day: These bulbs will grow when the day length is at least 12 hours long, although they will not likely form in northern gardens.

Sowing onions indoors: You can also choose to grow your onions either outdoors or outdoors by sowing them. If growing them indoors, you should sow your onion seeds in modules during the winter and store them in a greenhouse with temperature set between 10-16°C. Growing between three to four onions per module will help save space, and sowing up to six means that you can thin them out up to four plants. Harden out the plants during the spring before you transplant them in the ground. From here, multi-seeded onion modules will form into bulb clumps.

Sowing onions outdoors: When the soil is drying out and starting to warm up (usually between the end of winter and mid-spring), this is the best time to sow your onions outdoors. Sow the seeds 1.3cm deep in rows that are 20cm apart. Once done, thin out the seeds upto 5cm apart, and gradually up to 10cm. However, if you decide to plant them closer together, you will get more bulbs and a larger round of crops, but smaller onion bulbs will be developed.

How To Plant Onions

Growing onions are relatively easy when purchased in sets, as they have a faster growth rate, and are less prone to diseases. Bolting is more likely to occur, though, a process where the plant will emphasise the growth of the flower rather than the bulb. Heat-treated sets are a better alternative so that bolting will not occur. You can purchase onion bulb sets from most garden centres or online stores.

Plant a set of onion bulbs during spring. Whilst certain cultivars can be planted in the autumn, this is not advised since soil can be prone to water which leads to it getting heavy. This will cause the crop to be vulnerable to disease.

Organic produce will help the growth of onions since they have a limited root system, and organic matter will improve the soil. Avoid using fresh manure. Instead, include general fertiliser that has a high amount of potassium, like Vitax Q4.

(Video) 5 Tips How to Grow a Ton of Onions in One Container or Garden Bed

Add the sets within a 2cm depth of loose soil, and the tip should poke up from just above the surface. Space each bulb up to 10cm apart, with rows 25-30cm apart. Firm the soil and water them appropriately. Cover the bulbs with a fleece to prevent birds from interfering with them.

Alternatively, if you wanted to save having to weed the bulbs, then using a black weed-suppressing membrane on the ground will prevent weeds from coming through. You will have to plant the bulbs through the slits of the membrane.

Check out these 10 benefits about onions.

Growing Onions: Top Tips On How To Grow Bigger Onions | Polytunnel Gardening (1)

How To Care for Growing Onions

Watering/feeding: You should water the onions when there has been a continuous dry spell every 14 days and help monitor the growth by using a general liquid fertiliser. If the onions swell up during the summer, then stop your watering and feeding process. Watering overhead can provoke fungus to appear, so avoid doing this.

Autumn-planted onions need nitrogen-rich fertiliser in the winter to provide them with extra sulphate of ammonia which will help the flower to grow quicker. Dry poultry manure can be used too for this.

Weeding: Avoid planting onions alongside other plants as they will not grow well. Weed your onions regularly and by hand as opposed to using a hoe as this can damage the bulbs. Weeds can easily grow and swarm your onion patch, so ensure you monitor this.

Removing flowers: Onion flower stems can be removed as they gradually form because otherwise, the plant will focus its growth on the flower rather than the onion bulb.

Explore these delicious onion recipes.

How To Harvest Onions

Autumn-planted onion sets are ready for harvesting usually between early to mid-summer, whilst spring-sown or spring-planted onions are ready for harvesting between late summer and early autumn. The foliage will turn yellow to show the maturity of the plant. You should harvest them now before the foliage begins to break down. Do this by gently lifting them out with an appropriate instrument so that the bulb will not be damaged.

Store autumn-grown onions during the beginning of winter, whilst spring-grown ones will last into spring. Place the onions on a suitable drying rack upside-down and allow them to ripe outdoors in full sunlight for two weeks; you can also use a greenhouse or well-ventilated shed for this if the weather is unsuitable. The foliage needs to be dry before you store it away. If you need help with how else to harvest onions, we have a helpful guide to contribute to this.

Growing Onions: Top Tips On How To Grow Bigger Onions | Polytunnel Gardening (2)

How Do I Get My Onions to Grow Bigger?

Because growing onions is easy, there are a few simple steps to follow so that you can get bigger and better results out of them.

Choose A Good Variety

With the right variety of onion, you will find that they will grow bigger in next to no time. Depending on your area of living, each of the three onion types (long-day, intermediate-day, and short-day) show different results varying on how much sunlight they receive. Avoid using bunch onions or shallots since these will not form into large onions.

Plant Them Early

Getting your onions planted early will save more hassle in the long run. Growing onions from seeds can be grown indoors between the end of winter and the beginning of spring for a head start. Onions have a tolerance rate towards light frost and can even be grown up to mid-spring.

(Video) How to Grow Large Onions Perfectly Every Time

Spread Onions Out

Growing onions within a space of 3-4 inches will have a better growth rate. This will also help with nutrition so that they will each get a good amount of water and sunlight.

Grow an Enormous Onion Batch

You do not have to hesitate to grow a large onion batch of your own, mainly because they are so quick to grow and easy to maintain. By following this guide for growing onions, you will surely find great results within a matter of weeks by measuring when you plant them and how much nutrients they need to grow. You will not be disappointed by the time you harvest them.

How long does it take to grow an onion?

Onions can grow quicker than other vegetables. When grown from seed, onions should take between 3 to 4 months to mature to full growth. If you are growing onions from a set, these will grow quicker within six weeks. For large onions, plant the bulbs at least 10 to 12 inches apart and just below the soil surface.

What month can you plant onion sets?

You can purchase onion sets from between early spring to late summer from any garden centre or online stores. Plant your onion sets between mid-March and mid-April, although others can be planted between October to mid-March as well. These types of onion cultivars are less vulnerable to the cold.

Do onions need a lot of water?

You should feed your growing onions up to 1 inch of water every week; if there is a continuous spell of dry weather, they will need watering more regularly.

Do onions need full sun?

The best way to get bigger and better results from your onions is by growing them in full sun whilst keeping their soil really fertile and slightly acidic.

(Video) The Easiest Way to Grow Onions!


Related posts:

  1. The Best Ways to Use Strawberries
  2. How To Grow Your Own Food For Free (From Vegetable Scraps)
  3. Why ‘Bolting’ Is Not Always a Bad Thing

Growing Onions: Top Tips On How To Grow Bigger Onions | Polytunnel Gardening (3)

Sean Barker

Sean Barker is the MD of First Tunnels, and is enthusiastic about providing quality gardening supplies to gardeners across the UK

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