How to Grow Onion and Shallot Sets

Onions are an incredibly versatile vegetable for home cooking that are simple to grow and store well too. So, the experience of growing your own onion sets and shallot bulbs can be highly rewarding. In this growing guide, we’ll be detailing how to plant and grow onion and shallot sets with instructions for each growing step. There are various ways onions can be grown, with different advantages for each. So, first, take a look at our guide on the best way to grow onions to find out which best suits you. If you would prefer to grow onions from seed, our guide on how to grow onions and shallots from seed can help you with expert advice.

After unpacking your onion or shallot sets, put them into a cool, light, well-ventilated and frost-free place, away from direct sunlight.

You should choose a planting site with free-draining soil that will have plenty of exposure to sunlight. Once you’ve done so, prepare the soil by digging over and incorporating some general-purpose fertiliser. Then, work the soil down to a fine tilth as if preparing a seed bed.

Remove any loose papery skins before planting the sets. Push the sets into the soil at the base of the drill, with their pointed tips upwards. Spacing can be anything from 2.5cm (1in) to 10cm (4in) apart, depending on the size of bulbs. Closer spacing results in large numbers of small bulbs, whereas wider spacing results in a smaller number of large bulbs; 5-7.5cm (2-3in) usually works well.

Fill in the drill with soil by running the edge of the rake along its edge to draw soil over the sets, or use the trowel in a similar fashion. Use the trowel to firm in the sets. When they are planted, the tips at least should still be protruding from the soil surface.

How Deep to Plant Onion and Shallot Sets?

Onion and shallot sets are planted into a shallow drill (groove) in the soil, created with a string line and a draw hoe, or by laying a plank across the bed and running a trowel along its edge. The drill should be about the same depth as the set, or a bit less for some of the longer sets (many shallots, for example).

When Is the Best Time to Plant Onion and Shallot Sets?

Winter-hardy varieties of onions and shallots can be planted in early autumn. Otherwise, you should plant between February and April, as soon as the soil is sufficiently dry and warm; in practice this is usually late winter or early spring for sandy soils, and mid-spring for clay-based soils. Heat-treated sets (which have had their flowering potential suppressed, so are bolt-resistant) should not be planted before late March or April.

Onions and shallots form a bulb when the temperature and the number of daylight hours hit the right combination, which triggers their clock. Until that happens, they use daylight to produce a good deal of top growth before they form bulbs (and the more top growth, the bigger the bulb).

When the daylight reaches the right number of hours for that variety of onion or shallot, it will stop forming top growth, and form a bulb instead. The size of the bulb that eventually forms depends on the size of the "stalks", and the number of them. There will be one ring in the onion or shallot for every stalk that is formed, and the larger the stalk, the larger each ring will be. Bulb formation will pause, though, during dry, very hot or very cold weather.

Watering

In the spring, there is rarely the need to water newly planted sets. However, in dry spells later on in the summer and autumn, new plantings of overwintering onion and shallot sets should be watered in after planting. You should water them if the weather is dry, but not otherwise. You should stop watering once the onions or shallots have swollen and pull back the covering earth or mulch to expose the bulb's surface to the sun.

Feeding

You should feed your onion and shallot plants occasionally with a nitrogen-rich fertiliser (you can find onion, shallot, and garlic fertiliser in our shop). You should feed an autumn-sown crop with a liquid fertiliser in March.

<h3>Mulching</h3>

Mulching your onion and shallot sets is useful for cutting down watering and suppressing weeds. This can be done with a thick layer of shredded leaves, grass clippings or clean straw.

Weeding

The area you grow your onions or shallots should be weeded frequently, as onions don’t grow as well when surrounded by competing plants, leading to a smaller bulb size. To avoid damage to the bulbs, it is best to weed by hand.

Removing Flower Stems

You should break off any flower stems which appear, as this will impact the growth of the bulb and the ability to store them.

When the bulb is mature, the foliage turns yellow and topples over. Leave the sets for two weeks, and then carefully lift them with a fork, such as a Darlac garden fork, on a dry day.

Onions or shallots that are not for immediate use must be dried. Spread out the bulbs on sacking or in trays; outdoors if the weather is warm and sunny, or indoors if the weather is wet. Drying will take 7 to 21 days, depending on the size of the bulbs and the air temperature. Inspect the bulbs carefully: all soft, spotted and thick-necked onions should be set aside for kitchen use or freezing. The rest can be stored.

Store in trays, net bags, or anything where the air can circulate. Choose a cool and well-lit place to store them, where they will keep until late spring.

Onions and shallots aren’t typically prone to problems as an easy-to-grow vegetable. However, there are some things to bear in mind:

• Bolting - Otherwise known as flowering, bolting can occur as a result of lower temperatures in spring, so any flower heads should be snipped at the top of the stalk.
• Birds - Birds can pull up newly-planted onion and shallot sets, so garden netting can help protect them.
• Fungal diseases - Onion and shallots can be susceptible to certain fungal diseases. However, these are generally avoided if stored correctly and kept from damp growing conditions.

At D.T. Brown Seeds, you can get started on growing onions or shallots by shopping our range of quality onion, garlic, and shallot sets, in addition to onion seeds and onion plants for alternate methods of growing. You can also find much more gardening advice from our experts on our gardening blog, where you can find growing guides for all kinds of produce. If you’d like to find out more about our range of vegetable garden seeds and plants, fruit seeds, and fruit plants, don’t hesitate to get in touch and we’ll happily answer any questions you may have.