When to plant allium bulbs for beautiful, long-lasting blooms – don't leave it too late

A true gardener's favourite, alliums make striking additions to any garden. Learning when to plant allium bulbs will help you secure vibrant displays next season.

These architectural blooms make a bold feature of garden border ideas, and they're on our list of the best spring bulbs for cut flowers. Buying them ready-grown can be expensive, so learning how to plant bulbs is a brilliant budget garden idea if you're trying to cut costs.

'Bulb planting is arduous work, but rewarding,' says garden designer Harriet Worsley. 'Don’t leave it too late, as the ground will be frozen and hard.'

Knowing when to plant bulbs for spring is one thing, but if you're wondering when to plant allium bulbs specifically, here's what you need to know...

When to plant allium bulbs

Before we get started, it's worth noting that Allium encompasses a wide range of plants.

'Alliums are quite a broad family of plants, from onions, leeks and garlic, to the most amazing flowers that stand proud in any flower bed!' says Joseph Clark of @JoesGarden fame.

We're covering when to plant ornamental allium bulbs for vibrant spring and summer flowers.

Joseph Clark

As a child, Joe spent a lot of time with his great grandmother in the garden, learning about the different plants, growing fruit and veg and spotting all the animals in the garden. Nowadays, Joe utilises his abundance of innovative growing ideas to create easy and fun recipes to help his audience lead more healthy and environmentally friendly lives (whilst also saving money).

So, what is the best time of year to plant allium bulbs?

'We recommend planting alliums in the autumn,' says Josh Novell, gardening expert at Polhill Garden Centre. 'Alliums like full sun and well-drained soil, and work well when mixed in with other perennials.'

If you're wondering which end of autumn is best to plant your allium bulbs, it's better to do it sooner rather than later.

'The bulbs for flowering alliums are, in my experience, best planted in early to mid autumn – which for me is mid-October,' says Joseph.

It's important to make sure you plant them before the first frosts, while the soil is still relatively warm.

'Planting flowering alliums in October gives them ample time to establish roots over the winter,' adds Andrew O'Donoghue, co-owner of Gardens Revived. 'This, in turn, means that they should bloom beautifully from late spring to early summer.'

Andrew O'Donoghue

RHS-trained gardener Andrew O'Donoghue set up Gardens Revived with his brother, Christopher, in 2018 to create a thriving family business. Together, they have worked on residential gardens, listed buildings and gardens, flower shows and large estates with some exceeding 70 acres – many with historical significance.

Once you've decided when to plant allium bulbs, be sure to find the perfect spot in your garden for them.

Choose a sheltered location with free-draining soil to provide your plants with the conditions they need to thrive, and make sure you know how deep to plant allium bulbs for the best results.

'Only plant healthy bulbs with the root side down – or sideways if you're unsure, as they will usually right themselves while growing,' advises Joseph.

The question of whether spring bulbs should be soaked before planting divides gardeners, but generally, alliums bulbs don't require soaking before they enter the soil.

Best places to buy allium bulbs

Now that you've figured out when to plant allium bulbs, you can start selecting your stock. Allium crisophii, with its large, showy, globe-like bunches of tiny flowers, is a great way to make a splash in your garden borders, while tall alliums such as Allium stipitatum ‘Mount Everest’ will add some structure.

Late-flowering alliums like Allium sphaerocephalon are a great way to add colour to your garden over the summer. And, if you're looking for north-facing garden ideas, try something like Allium moly ‘Jeannine' – it's brilliantly suited to woodland conditions.

Whichever style you prefer, try shopping from the following stockists:

• Crocus has a wide variety of flowering allium bulbs, like the classic Allium hollandicum 'Purple Sensation'
• Thompson & Morgan, too, has a plethora of allium bulbs on offer – try Allium stipitatum 'Mount Everest', mentioned above
• Sarah Raven is also a great spot to shop a variety of allium bulbs – for something a little different, try Allium schubertii 'Magic'
• Amazon is a surprisingly brilliant source of flowering allium bulbs, too!

Once you've chosen your allium bulbs, all you have to do is plant them! Make a hole about four times the diameter of the bulbs, and plant smaller growing alliums 7.5-10cm apart.

Taller species, meanwhile, need at least 20cm between the bulbs. All varieties can be planted in containers, but they prefer not to be planted when it's cold and wet outside – so best be quick and get yours in the ground before October ends.

Good luck!

FAQs

What month is best to plant allium bulbs?

The best time of year to plant allium bulbs is October when the soil is warm enough for the roots to establish themselves before the winter chills take hold. Planting later can risk weaker plants and a subsequent shorter blooming period. Plus, the variety on the market will be slimmer – so stock up and get planting before it's too late!

Can you leave allium bulbs in the ground all year?

Like many spring-flowering bulbs, allium bulbs can be left in the ground all year. However, it's best to choose a suitable location when initially planting – heavy, wet soils can lead to rotting, so ensure the soil surrounding your allium bulbs is well-draining, but never too dry.

Now you know when to plant allium bulbs, you can start preparing your spring garden.