The Ultimate Guide To Growing Allium Bulbs - DIY Gardening

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How to Grow Allium Bulbs

Written by Hannah Miller. Reviewed and Fact Checked by Elizabeth Smith. Published to Spring Plants. Updated: 18th February 2023.

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Alliums are popular spring and early summer-flowering bulbs that produce distinctive globe-like blooms atop long stems. I’ve been growing them for years and have fallen completely in love with them.

I’ve experimented with growing them in clusters, but they also mix well with other spring and early summer plants, such as tulips, irises and even hardy geraniums.

Key points:

1. There are lots of alliums to choose from, with some blooming much later than others.
2. I grew the huge “Globemaster”, which produced a ball-shaped bloom over 15cm/6″ wide.
3. I think alliums look delightful set amongst tall grasses.
4. Alliums are related to the onion, and I know from my experience that most pests stay away from them.
5. The alliums in my garden flower for several weeks in late spring and into early summer.
6. I actually like the look of the faded flowers which hold interest well into summer.
7. I’ve never had issues growing alliums and would describe them as low-maintenance.

Size

Height: From 50cm to over 1m (20-40″)

Spread: From 30cm to 60cm (12-24″)

Type

Deciduous bulbous perennials: Alliums die back after flowering in the summer and reappear the following spring

Growth

Reaches full height in year 1 and may set seeds

Difficulty

Very easy to grow

Native

Most are native to the northern hemisphere

Location

A free-draining spot sheltered from the wind if possible

Sunlight

Full sun

Hardiness

US zone 3-8 and all parts of the UK

Water & Feed

Water once after planting and then only in spring if the soil is dry

Companions

Often set amongst grasses but can be mixed with a variety of late spring and early summer plants, alliums are very versatile

Planting

In the autumn, dig a hole 3 times the height of the bulb and cover with soil

Flowering

Late spring – May and June

Allium giganteum opening

Allium purple sensation

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How to Grow Allium Bulbs

How and When are Alliums Sold?

Alliums can be grown from seeds, but when I tried, I found that most failed, and every gardener I know buys bulbs in the autumn for planting straight away.

The bulbs require a period of cold temperature before they can grow, so I suggest you buy them early and get them into the ground by mid-autumn so they have plenty of time to settle in.

Where is the best location to grow alliums?

Alliums prefer full sun but will still grow in light shade. I’ve had a few perform poorly when I grew them in a shaded part of my garden so moving forward, I’ll place them in the sunniest position possible.

I’ve had a few of the taller alliums snap in the wind so if you live in an exposed area, consider where you grow them carefully.

How should the ground be prepared?

In most cases, no special ground preparations are required. If the soil is moisture retentive, add some grit and work into the soil to improve drainage. I’ve done this as my garden has very heavy, sticky soil and it certainly improved the drainage and aeration.

How much water or fertiliser do alliums require?

Water the allium bulbs immediately after planting and then leave them alone, only water in the spring if the soil is parched.

Alliums are drought tolerant and should never sit in water, although potted alliums will require more regular irrigation, but make sure the pot can drain excess water.

I’ve never felt the need to fertilise alliums in my garden and would only consider it if the soil was very poor.

How tall and wide will alliums grow?

Some cultivars can grow over 150cm (59″) tall, but most of the alliums in my garden reached heights between 40cm (16″) and 1m (40″).

Most alliums produce a single globe on top of a single stem, so their spread above the ground is minimal, but the foliage can spread up to 50cm (20″).

I grew the famous allium Globemaster and while the globes were huge and eye-catching, the stems didn’t grow very tall, and I was a bit disappointed overall.

Should I prune or deadhead alliums?

You can deadhead the bloom by cutting off the stem at the base; although this is optional. I personally like the faded blooms as they hold interest into the summer, but they do make excellent cut flowers as well.

The foliage should be left to die back naturally, so energy is sent to the bulb, preparing it for the next season.

While the foliage is well known for being unattractive, I don’t recommend cutting it off or tying it in knots as this reduces photosynthesis and can weaken the bulb.

Are there any pests or diseases of concern?

Allium bulbs are related to the onion and they repel many pests. I’ve never had issues with bugs or diseases although there are a few issues of concern:

Diseases:

• Onion rot.
• Downy mildew.

Pests:

• Slugs and snails.(never bothered mine, but I have heard stories)
• Allium leaf miner.

When do alliums flower and how long for?

My alliums bloomed in May and June for around 3 weeks. The drumstick allium (sphaerocephalon) is a late starter and mine bloom from early to mid-summer.

Can alliums be propagated to create more plants??

Some alliums readily self-seed and spread easily but I’ve never experienced this in my garden. Gardeners can collect the seeds or dig up and split the bulb offsets every few years.

Are alliums toxic or harmful to humans and pets?

Alliums are toxic to cats and dogs but not to humans.

Source.

Are alliums beneficial to wildlife?

All alliums are beneficial to pollinators, and I’ve seen a few enjoying the alliums in my garden.

(Source)

The alliums are also of interest to many insects too.

Can alliums be grown in pots?

Alliums can be grown in pots, and I have tried this, but consider that:

• They will require more frequent watering, and as the bulbs dislike waterlogged soil, the pot should have plenty of holes for drainage.
• The pot should be deep as alliums are top-heavy plants.

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Growing Allium Bulbs: At a Glance

I’ve been testing and experimenting with alliums over the last 8 years and below I share 10 tips with you:

1. Plant in the autumn so they can go through a cold period – which is required for them to grow in the spring.
2. Bury the allium bulbs to a depth 3 times their height.
3. Allium bulbs tolerate various soil types but will rot in soggy conditions.
4. They flourish in full sun, but they will grow in light shade, yet rarely in deep shade.
5. Keep away from windswept parts of the garden, as the stems are fragile and may snap (happened several times to me).
6. Allium foliage turns yellow and starts to fade even before the flower has appeared; you can hide the ugly leaves by planting them further back in the border or by choosing other plants that will smother them (hardy geraniums work well).
7. Alliums make for lovely cut flowers.
8. I also feel that they maintain interest in the garden well after the blooms have faded.
9. Propagate via seeds or bulb offsets, which can be removed every few years – I’ve had better luck with bulb offsets than seeds.
10. Grow with other spring-flowering bulbs, mix with ornamental grasses or pot them up as a feature.

When Alliums Flower

This infographic gives you an idea of when alliums flower, but in general, most will come into bloom in May and June:

How to Hide Allium Foliage

One complaint I have is with regards to the foliage, which even at its best doesn’t look pleasant but worse still, it fades to a sickly yellow colour even before the blooms appear.

If you’re planning on growing alliums in a border, you’ll probably want to mask the foliage.

Here I have a few suggestions:

1) Grow lavender in front of the alliums as they will hide much of the low-level foliage.

2) Hardy geraniums are my go-to perennial for filling space, and they easily cover the fading allium foliage in my garden each year.

3) Hostas are reliable plants with plenty of foliage that will cover the ground area at the base of the alliums.

4) Tiarella is a popular spring and early summer perennial known for its ground-covering foliage.

5) Blue-eyed grass – a grass that isn’t a grass but does provide cover just above ground level.

6) Peonies are stunning late spring and early summer plants that bloom at the same time as alliums, and they produce plenty of foliage.

How to Care For Alliums After They’ve Flowered

I’ve always found alliums, and their bulbs, are easy to care for but consider these points:

While rather untidy and messy, the foliage shouldn’t be removed or tied in knots; instead, it should be left to die back naturally so the plant can photosynthesise and send energy to the bulb, which prepares it for next season’s growth. As a general rule of thumb, only remove the foliage when it pulls away easily from the bulb.

Some allium varieties will spread via seeds, so if you don’t want to see offspring shooting up all over the garden, deadhead after flowering.

If you want to grow more alliums, you can lift the bulbs after the foliage has entirely died back and remove the bulb offsets; these can be planted straight away and will grow reliably.

There is no need to apply fertiliser or excessive amounts of water to the allium bulb after flowering. In fact, it should be left alone and the soil kept on the dryish side, as this prevents bulb rot.

Recommended Alliums

A decade ago, I would be lucky to find more than 10 allium varieties in the UK, but now there are dozens to choose from, and cultivators are working on creating alliums that will flower well into the summer.

If you’ve never grown alliums before, I suggest you start with these:

1) Purple Sensation

This is the most common allium and was the first I grew; it flowers early and is mass-produced, meaning it’s also one of the cheapest alliums you can buy. It reaches around 75cm/30″ tall and produces globed blooms reliably. The purple sensation is the best allium for beginners.

2) Globemaster or Giganteum

Giganteum is one of the tallest alliums, reaching up to an impressive 1.5 metres (5′), while the Globemaster is shorter at 80cm (31″) but produces a famously large flowerhead up to 20cm (8″) wide. When I grew the Globemaster, I was disappointed with the height, it looked quite short considering the size of the globe, which was huge.

3) Drumstick Alliums

This variety blooms slightly later and in my garden, it put on a show from early to mid-summer, and the blooms are a completely different shape. The allium head starts off green and gradually changes to purple making it an eye-catching plant.

Companion Plants

In addition to masking the ugly allium foliage, there are many plants that I feel would look wonderful next to alliums. I’ve tried a few of these over the years but the Cranesbill is my number one choice:

Peonies

Tulips

Iris

Oriental Poppies

Cranesbill

Anemones

Wallflowers

French Lavender

Also consider:

• French lavender

Elizabeth Smith’s Tip

Here is a quote from Elizabeth Smith, who frequently fact-checks our content:

While alliums are easy to grow and look wonderful dotted around the garden, the yellowing foliage can ruin their appearance unless it’s masked by other plants.

For beginners, I recommend hardy geraniums as they provide plenty of airy, light foliage and dainty blooms. They’re my go-to plant for filling voids and hiding things in my garden.

More Allium Photos

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This guide was reviewed and fact-checked by qualified horticulturist Elizabeth Smith.

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Meet The Author: Hannah Miller

Hannah is a keen gardener who grows organic fruit and vegetables in her Surrey garden and is moving towards a more sustainable lifestyle. 

She is also the proud grower of a dahlia and herb garden.

Hannah worked for the NHS for 12 years but also has a level 3 qualification in horticulture and is currently studying for her level 4.

More About Hannah Miller

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