How to grow alliums

Inspired by a helpful UK gardening guide. This walk-through draws on the "How to grow and care for alliums" video from the Love the Garden UK channel - the online home of Miracle-Gro in the UK. It covers choosing bulbs, planting depth, and what to do with alliums after they've finished flowering. Straightforward advice for any UK garden.

1. Understand the difference between ornamental and edible alliums

The allium family includes garlic, onions, leeks, and chives - but when gardeners talk about alliums as a border plant, they mean the ornamental kinds. These are grown for their striking spherical flower heads on tall stems, not for eating.

Popular ornamental varieties include Purple Sensation (deep violet, about 80 cm tall), Globemaster (large purple globes, up to 90 cm), and Christophii (silvery-purple, shorter stems, lovely dried seedheads). Christophii is particularly good if you want to leave the heads on for structural interest through summer.

2. Plant bulbs in autumn

Allium bulbs go in from September to November, before the ground gets too cold. They need a period of cold to develop properly, so autumn planting is the way to go - don't try to rush them in spring.

Bulbs are widely available from garden centres from late summer. Buy firm, dry bulbs with no soft spots. Bigger bulbs generally produce bigger flower heads, which is worth bearing in mind if you're after impact.

3. Plant at the right depth

The general rule for bulbs is to plant at a depth of three times the bulb's diameter. For a medium allium bulb that's roughly 5 cm across, that means about 15 cm deep. For larger bulbs like Globemaster, go deeper - 20 cm or more.

Space them at roughly 15–20 cm apart for a natural, slightly informal look, or closer together if you want a more packed display. They don't mind being a bit crowded.

4. Drainage matters more than almost anything else

Alliums really don't like sitting in wet soil over winter. Waterlogged ground will rot the bulbs before they even get started. If your soil is heavy clay, improve it by mixing in plenty of coarse grit before planting, or raise the bed slightly.

In a pot, use a soil-based compost mixed with grit, and make sure the pot has proper drainage holes. A terracotta pot works particularly well for alliums - it breathes, which helps prevent the sodden conditions they hate.

5. Choose a position in full sun

Alliums want full sun, or at the very least most of a day's sunshine. They'll manage in partial shade but tend to produce smaller flower heads and sometimes flop a little on the stems.

A south or west-facing border is ideal. In Kent, most gardens get plenty of sunshine through May and June when alliums are in their prime, so you don't generally need to worry too much about this.

6. Leave the foliage while it dies back naturally

Allium leaves tend to look a bit tired and tatty by the time the flowers appear - they often start going yellow and flopping over while the flower heads are still at their best. This is completely normal and not a sign of a problem.

Don't cut the foliage off while it's still green. The bulb needs it to photosynthesise and store energy for next year. A useful trick is to plant alliums near later-emerging perennials - hostas, geraniums, or grasses - so the foliage gets hidden as the season progresses.

7. Leave seedheads for structure

Once the flowers are over, the spherical seedheads stay attractive for weeks. Leave them on - they look particularly good in late summer when they've dried and gone a straw colour, and they catch the light well. Bees and other insects use them too.

Cut the stems back to the ground once the seedheads have fully dried, or in autumn before new growth begins. This also gives you the chance to collect seed if you want to try growing them on, though seedlings take a few years to reach flowering size.

8. They spread naturally over time

Established alliums produce offsets around the parent bulb, so clumps gradually build up over the years. You can leave them to naturalise, or lift and divide them every few years to keep the display looking its best and spread them to other parts of the garden.

Dividing is best done in autumn, when the bulbs are dormant. Carefully lift the clump, separate the offsets, and replant at the same depth. It's a simple job that takes ten minutes and keeps the planting looking fresh.

When to call a handyman

Planting alliums is a pleasant half-hour job in the garden. What sometimes needs a bit more effort is the preparation beforehand - clearing old planting, improving drainage in a heavy border, or building a raised bed where the drainage conditions can be properly controlled. That's the kind of work Richard can take on.