When To Plant Allium Bulbs In The UK

Allium Gladiator

Alliums, also known as ornamental onions are a very easy modern cottage garden plant to grow. Grown for their showy blooms that come in a wide range of sizes and shades of blue, purple, white and yellow. If you wish to add this attractive plant to your garden then you should plant allium bulbs in early autumn.

Where To Plant Allium Bulbs

Allium bulbs should be planted in full sun where they are sheltered and have well-drained soil, they do not like cold, exposed or waterlogged conditions. Some smaller varieties do well in cooler and moister conditions such as allium moly.

Allium Moly

Depending on the height of the allium you wish to plant, they can be planted in the front or back of your border.

How To Plant Allium Bulbs

Planting In The Ground

Plant allium bulbs 4 times the size of the bulb below the surface of the soil, pointy side up. Space smaller varieties of alliums 3-4in (8-10cm) apart, taller alliums need at least 8in (20cm) between the bulbs.

Planting In Pots

Most allium bulbs will do well in deep pots. Plant the bulbs in a multi-purpose compost and water thoroughly.

If you wish to plant allium bulbs in a pot make sure it has adequate drainage. Place pieces of broken pots or stones at the bottom of the pot to assist with free drainage and air circulation.

Feeding Alliums

Allium in flower

Feed your alliums with a potash-rich fertiliser when they are in flower and water them if no rain is forecast.

Blood, bone and fishmeal generously scatted around each clump will be greatly appreciated too.

When Do Alliums Flower?

Allium Coming Into Flower

Alliums planted in the autumn will flower in the following spring and early summer.

Why Are My Alliums Not Flowering?

The main reason for alliums not blooming next spring is “bulb blindness” and the main culprit for causing this is an impatient gardener removing the leaves too prematurely the previous year or if they were hit by a late frost.

Bulbs cannot replenish their energy reserves if they cut back too early. The leaves need to be allowed to die back naturally for as long as possible before cutting the foliage back.

Don’t tie up the foliage once flowering has finished either, many gardeners do this to tidy up their appearance but this also interrupts the plant’s process of storing energy for next year’s blooms.

If untidy alliums bother you that much, lift the bulbs and plant them in unused pots or another part of the garden until they haven’t died back completely.

Other reasons for “bulb blindness” are:

  • Overcrowding
  • Shallow planting
  • Allowing seed heads to form
  • Lack of nutrients in the soil

Can You Deadhead Alliums?

Spent Allium Flower

It is a good idea to deadhead alliums once their blooms are spent as this prevents them from wasting energy forming seeds, energy that can be used to build up the bulb for next year’s show of flowers.

Alliums make excellent cut flowers, but like all bulbs, it is best if you minimise the number of leaves you cut when you pick the flowers.

When you cut, make sure you leave a short section of the leafy part of the stem to give the bulb a chance to make enough food to survive through the dormant period.

Change the water regularly to minimise the oniony smell or add a drop of bleach to the water. They should look good for at least 2 weeks in a vase after cutting them from your garden.

Alliums are also very good for drying and are ideal for a dried flower arrangement.

Allium FAQ

Do Alliums Have A Fragrance?

As alliums are also known as ornamental onions gardeners often wonder if having them in their garden will make it smell more like an allotment than an outdoor oasis.

Thankfully the oniony scent is only sometimes detected when the leaves, petals or stems are crushed or bruised and is rarely noticed when planted in your garden.

Do Alliums Come Back Every Year?

Alliums are dependable perennials that will return year after year if given the proper care.

Do Allium Bulbs Multiply?

Many allium varieties multiply, once flowering is over and leaves have died down, lift the bulbs and detach the offsets. Plant them in the final position or grow on in gritty compost.

Are Alliums Poisonous?

While alliums are fine for human consumption, they are poisonous to cats and dogs.

Do Alliums Attract Bees?

Allium With Bee On

Alliums are an ideal plant to have if you wish to attract bee and butterflies into your garden.

They are also a good plant for repelling deer, rodents and other garden pests.

Allium Problems

Alliums suffer from the same diseases and pest problems as culinary onions such as onion fly, onion white rot and downy mildew, but they tend to be trouble-free when planted in borders.

Pests to be on the lookout for include allium leaf miner, slugs and snails.

Allium Facts

Allium in flower
  • Allium is a genus of monocotyledonous flowering plants that includes hundreds of species, including the cultivated onion, garlic, scallion, shallot, leek, and chives.
  • The generic name Allium is the Latin word for garlic, and the type species for the genus is allium sativum which means “cultivated garlic”.
  • The Swedish botanist Carl Linnaeus first described the genus Allium in 1753. Some sources refer to Greek αλεω (aleo, to avoid) by reason of the smell of garlic.
  • Various Allium has been cultivated from the earliest times, and about a dozen species are economically important as crops, or garden vegetables, and an increasing number of species are important as ornamental plants.
  • Allium species occur in temperate climates of the Northern Hemisphere, except for a few species occurring in Chile (such as A. juncifolium), Brazil (A. sellovianum), and tropical Africa (A. spathaceum).
  • They vary in height between 5 cm and 150 cm. The flowers form an umbel at the top of a leafless stalk. The bulbs vary in size between species, from small (around 2–3 mm in diameter) to rather large (8–10 cm). Some species (such as Welsh onion A. fistulosum) develop thickened leaf-bases rather than forming bulbs as such.