How to grow alliums

Alliums add structural interest to your garden
Image: Allium 'Lavender Bubbles' from Thompson & Morgan

If you know your onions, you’ll relish the prospect of planting allium bulbs in your flower beds as well as your veg patch. With their statuesque proportions and pompom heads, they offer extra colour during the spring and early summer and lend an architectural quality to your borders. Here we take a look at how to get the most from these spectacular bulbs.

Firework display

Allium 'Purple Sensation' makes a explosive display in any garden
Image: Allium 'Purple Sensation' from Thompson & Morgan

If you’re looking for a bold display and a splash of vibrant colour during the late spring and early summer before the rest of your planting reaches the peak of its crescendo, you can’t really go wrong with alliums. In particular, the taller stemmed plants like dazzling ‘Purple Sensation’ grow to about 3 feet in height with 6“ spherical blooms made up of a multitude of bold lilac flowers. By planting them at the back of your borders, you ensure these floral fireworks, which explode into bloom during May and June, provide a spectacular backdrop for the rest of your planting.

Early alliums

Spectacular seed heads create enduring structure
Image: Allium 'Schubertii' from Thompson & Morgan

If you’re looking for late winter colour, some alliums bloom from as early as mid February onwards, making them a must for your spring planting. Check out allium ‘Schubertii’ which, with its dainty pink florets, makes a wonderful early display. And as the blooms fade during mid to late May, you’re left with wonderfully architectural seed heads which add extra structure to your borders right through the growing season and beyond.

Alliums among your roses

Aphids hate the scent of alliums, but bees and other pollinators love to visit
Image: Allium caeruleum from Thompson & Morgan

Some are sniffy about growing alliums in their flower beds because, being from the same family as onions and garlic, there’s the potential for an oniony smell. But though these plants do produce a slightly garlicky odour, this is normally lost among the scent from your other flowers, besides which, though you might not be able to smell anything, aphids find the scent repellent, making this a fine flower to grow in amongst your roses.

Where to grow alliums

Allium amplectens is perfect for the front of a border
Image: Allium amplectens 'Graceful Beauty' from Thompson & Morgan

Alliums are a hardy bulb that tolerates a variety of conditions but which positively thrives in fertile, well-drained soils, in sun or semi shade. The only thing they really don’t like is heavy, waterlogged soil which can cause the bulbs to rot in the ground. Before planting, treat your soil to some well rotted compost or manure, and you’re set for a spectacular display come the spring.

The taller alliums like Purple Sensation tend to look best at the back of your border, but some of the smaller varieties like allium amplectens ‘graceful beauty’ grow to a less imposing maximum of around 12 inches, making it perfect for massing at the front of borders or for planting in pots.

How to grow alliums

Plant your bulbs deep to ensure the tall stems don't fall over
Image: Allium 'Big Impact Mixed' from Thompson & Morgan

Taller alliums present quite a large surface area, so you must take care to bury the bulbs deep enough to prevent the wind knocking the stems down. Typically, you should plant the bulb to a depth of four times the diameter of the bulb, allowing a minimum of 4 inches between bulbs. Tamp the ground down firmly, marking the spot where you planted the bulbs.

It’s best to plant your allium bulbs during the autumn – from September until the middle of November; being such a hardy bulb thought planting your alliums in December shouldn’t present a problem as long as you avoid doing so during hard frosts. Do plant your bulbs as soon as you can after you receive them or they may begin to dehydrate.

Caring for alliums

Make a statement in your garden with a more unusual variety- Allium 'Hair'
Image: Visions BV, Netherlands

As a tough bulb, alliums don’t need lifting each year, and in fact tend to do better when they’re allowed to establish over a number of seasons. Because the seed heads look so attractive, you may find that your plants self-seed and that, this being the case, you may wish to thin them out once in a while.

Simply mark the ground where your alliums are so that, when the foliage dies back, you can find them again. Dig them up, separate them and replant. Alliums like deep, rich soil, so they love the environment of your borders and kitchen garden and, along with your other plantings, will benefit from a mulching during the spring.

Coming from the same family as onions and garlic, your alliums are prone to the same pests and diseases that afflict their vegetable cousins. Onion white rot, downy mildew and onion fly tend to be less of a problem when growing alliums in borders, but it’s best to avoid planting them where you have previously grown onions.