How to Grow Onion & Shallot Sets

Few ingredients are as fundamental as onions and shallots. Almost every savoury meal begins the same way - with one gently sizzling in a pan. When something plays such a central role in the kitchen, it makes perfect sense to grow your own. Fortunately, onions and shallots are also among the most rewarding crops for gardeners of all abilities.

This guide focuses on growing from our onion sets rather than seed, because sets offer speed, simplicity, and a higher success rate - especially for beginners or those who want dependable results with minimal fuss. Sets are essentially small, dormant bulbs, already primed to grow as soon as conditions are right.

Alongside onions and shallots, we’ll also touch on garlic - together forming what we might call the ‘Allium Trinity’ of the kitchen garden. By following the steps below, you’ll grow healthy, full-sized bulbs, avoid common pitfalls like bolting and disease, and enjoy a crop that stores beautifully for months.

Step 2: Site Preparation

Soil: Alliums prefer firm, free-draining soil. Resist the urge to over-dig - loose, fluffy soil can lead to poor root anchorage and misshapen bulbs. Most importantly, onions and shallots hate sitting in wet ground.

pH: Aim for a neutral pH (6.5–7.0). If your soil is acidic, apply garden lime several weeks before planting.

Feeding: About a week before planting, rake in a balanced fertiliser such as Blood, Fish & Bone. This provides steady nutrition without encouraging soft, leafy growth at the expense of bulbs.

Step 3: Planting Guide

Although closely related, onions, shallots, and garlic each need slightly different treatment.

• Onions: Plant sets 10cm apart so they have space to swell, with the pointed tip just showing above the soil surface.
• Shallots: Space 15cm apart - they grow in clusters rather than single bulbs - so they need room to grow sideways. Again, leave the tip just visible.
• Garlic: Break the bulb into individual cloves and plant 2.5cm below the surface, spaced 15cm apart. Planting deeper protects against frost heave and curious birds.
  

Top tip: It’s common for birds to dig up newly planted sets because the papery skins look like worms or nesting material. To avoid this, cover newly planted beds with fleece or netting for the first three weeks until roots anchor the bulbs firmly in place.

Step 4: Care During the Season

Weeding: Weeding is absolutely vital. Onion leaves are thin and upright, offering little shade, so weeds quickly steal moisture and nutrients. A light, regular pass with an onion hoe makes a huge difference to final bulb size.

Watering: Water during dry spells, particularly in May and June, when bulbs are swelling. Consistent moisture now leads to heavier, healthier crops. Stop watering once the leaves begin to yellow, or the bulbs will rot in the ground.

The Bolting Panic: If a flower stalk appears, the plant has bolted. Snip it off immediately and use that onion straight away - it won’t store. To reduce the risk, use D.T. Brown’s Heat-Treated Onion Sets, which are specially prepared to prevent premature flowering.

Step 5: Harvesting & Curing

When to Lift: Wait patiently until the foliage naturally yellows and falls over. Don’t bend the necks yourself - this damages the bulb and invites disease.

Lifting: Choose a dry day and gently loosen the bulbs with a fork.

Curing: This step is crucial for storage. Lay bulbs on the soil surface in dry weather, or move them to a greenhouse or airy shed. Leave them for 2–3 weeks.

The Test: Bulbs are ready when the skins are papery, and the neck feels tight and dry. Only then should you store them. Onions will store for different lengths of time depending on their variety – eat your Red Barons first, and save your Sturons for winter!

Step 6: Troubleshooting & FAQs

Why did my garlic produce a single, solid, round bulb?

It was planted too late and didn’t experience enough cold to divide into cloves.

Can I plant supermarket garlic?

No. It’s often treated to prevent sprouting, but it carries a high risk of disease.

What is White Rot?

A serious fungal disease showing as white fluff on roots. There is no cure — avoid planting onions, leeks, garlic, or shallots in that soil for 8+ years.

What about Onion Downy Mildew?

This thrives in damp, overcrowded conditions. Space plants well, avoid overhead watering, and rotate crops - never plant onions where leeks or garlic grew last year.

Stock your pantry for the year ahead.

Home-grown onions and shallots are hard to beat - they’re flavourful, versatile, and store for months when cured correctly. By choosing sets, planting at the right time, and following a few proven techniques, you’ll enjoy a reliable harvest year after year.

Shop our full range of Onion Sets, Garlic Bulbs, and Shallots today and grow with confidence.

All our sets are guaranteed to arrive firm and mould-free upon arrival – that’s the D.T. Brown quality promise.