How to Grow Allium Bulbs

A popular ornamental spring plant with a unique rounded head

Part of our Spring Flowering Plants guide: By Daniel Woodley at DIY Gardening

Alliums are popular spring and early summer-flowering bulbs that produce distinctive globe-like blooms atop long stems. Grow this versatile plant in clusters to make a statement or mix them with other spring and early summer plants such as tulips, irises and hardy geraniums.

Key points:

  1. There are lots of alliums to choose from, with some blooming much later than others.
  2. Consider the huge “Giganteum“, which produces a bloom over 15cm/6” wide.
  3. Mixes surprising well with grasses.
  4. Alliums are related to the onion.
  5. The globes flower for several weeks in late spring and into early summer.
  6. Faded flowers still hold interest well into summer.
  7. Very easy to care for.

Size

Height: From 50cm to over 1m (20-40″)

Spread: From 30cm to 60cm (12-24″)

Type

Type

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

Growth icon

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 bloom just starting to open

Allium giganteum opening

Purple Sensation allium flowerhead

Allium purple sensation

How to Grow Allium Bulbs

How and When are Alliums Sold?

Alliums can be grown from seeds, but the most popular method is by bulbs which are sold in the autumn for planting straight away.

The bulbs require a period of cold temperature before they can grow; 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. Avoid fully shaded parts of the garden and ensure the spot is free draining as alliums hate wet feet and the bulbs rot easily.

Taller alliums should be grown in a sheltered location, so the stem doesn’t bend over or snap in the wind.

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.

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.

There is no need to fertilise alliums unless the soil is very poor.

How tall and wide will alliums grow?

Some cultivars can grow over 150cm (59″) tall but most reach heights between 40cm (16″) and 1m (40″).

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

Should I prune or deadhead alliums?

You can deadhead the bloom by cutting off the stem at the base; although this is optional, the faded blooms still hold interest in the summer but do make excellent cut flowers.

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

The foliage shouldn’t be tied in knots either as this reduces photosynthesis.

Are there any pests or diseases of concern?

Allium bulbs are related to the onion and repel many pests although there are a few issues of concern

Diseases:

Pests:

When do alliums flower and how long for?

Most alliums flower in May and June for around 3 weeks. The drumstick allium (sphaerocephalon) is a late starter and blooms from early to mid-summer.

Can alliums be propagated to create more plants??

Some alliums readily self-seed and they spread easily. 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.

(Source)

The alliums are also of interest to many insects too.

Can alliums be grown in pots?

Alliums can be grown in pots 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.

Buy Alliums Online

Allium Gladiator x 10 Bulbs Size 16 up Pretty Spring Flowers.
Humphreys Garden Allium Purple Sensation x 20 Bulbs + 10 Allium Drumstick
Allium Gladiator x 10 Bulbs Size 16 up Pretty Spring Flowers.
Humphreys Garden Allium Purple Sensation x 20 Bulbs + 10 Allium Drumstick
Allium Gladiator x 10 Bulbs Size 16 up Pretty Spring Flowers.
Allium Gladiator x 10 Bulbs Size 16 up Pretty Spring Flowers.
Humphreys Garden Allium Purple Sensation x 20 Bulbs + 10 Allium Drumstick
Humphreys Garden Allium Purple Sensation x 20 Bulbs + 10 Allium Drumstick

Growing Allium Bulbs: At a Glance

If you want to grow alliums from bulbs, consider these ten points:

  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, but rarely in deep shade.
  5. Keep away from windswept parts of the garden as the stems are fragile and may snap.
  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.
  7. Alliums make for lovely cut flowers.
  8. They also maintain interest in the garden after the blooms have faded.
  9. Propagate via seeds or bulb offsets which can be removed every few years.
  10. Grow with other spring-flowering bulbs, mix with ornamental grasses or pot them up as a feature.

When Alliums Flower

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

Allium bloom time chart

How to Hide Allium Foliage

One complaint gardeners often 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 are 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 the go-to perennial for filling space, and they’ll easily cover the fading allium foliage.

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

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.

There were barely 10 varieties to choose from a decade ago, but now there are dozens, and cultivators are working on creating alliums that will flower well into the summer.

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

1) Purple Sensation

This is the most common allium; 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.

3) Drumstick Alliums

This variety blooms slightly later, usually from early to mid-summer, and the blooms are a different shape. Initially green, the colours of the flowers gradually change to purple.

Companion Plants

In addition to masking the ugly allium foliage, there are many plants that look wonderful next to alliums:

Also consider:

Hannah’s Tip

Here is a quote from Hannah, our co-founder:

While alliums are easy to grow and look wonderful dotted around the garden, the yellowing foliage can ruin their appearance unless its 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

Closeup of a purple allium flowerhead
Purple allium bloom against a green hedge background
Allium drumsticks in a border
Allium purple sensation flowerhead

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How to grow alliums

Author: Daniel Woodley

This guide to growing allium bulbs for late spring and early summer colour was lovingly created by Daniel Woodley here at DIY Gardening and was last updated in February 2022.

Discover more spring-flowering bulbs and plants here.

Daniel is a keen gardener who also manages a large residential landscape in addition to his own mid-size garden.

He also enjoys experimenting with vegetables and fruits in his garden but with varying success!

More About Daniel Woodley

Danny Woodley

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This allium bulb growing guide was published by DIY Gardening

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