Alliums are popular summer-flowering plants which are worth the reward in garden borders. Find out the answers to Google’s most-asked questions on these striking plants.

Interestingly alliums are a plant that is predominately native to temperate and subtropical regions of the Northern Hemisphere. But according to the experts at Kew, they are also native to South Africa too. They have been introduced to parts of South America, Africa, India, Australia, and New Zealand.

Where are Alliums native to?

Interestingly alliums are a plant that is predominately native to temperate and subtropical regions of the Northern Hemisphere. But according to the experts at Kew, they are also native to South Africa too. They have been introduced to parts of South America, Africa, India, Australia, and New Zealand.

Allium in native south africa

Are Alliums annuals, biennials, or perennials?

Alliums are perennial plants grown from bulbs which will return to brighten up your garden, for around three to four years after you plant them.

Which garden style are they best suited for?

Alliums are great in several garden styles, from chocolate box cottage-style gardens to simple prairie-style displays. Iris and Nepeta (commonly known as Catmint) will flower at the same time as alliums giving a real wow to any setting.

Alliums in cottage style garden border

How do you grow Alliums from seed?

You can grow alliums from seed, you can even collect them from the dried flower heads post-flowering. But for the greatest chance of success, it’s best to sow the seeds as soon as possible after ripening. The seeds of species Allium will usually be identical or similar to the parent plant, but seeds collected from hybrids won’t be ‘true’ to the parent plant. But most gardeners will choose to grow them from bulbs. Available from your local garden centre, you plant the bulbs in early to mid-autumn.

Alliums can be grown in containers or in border that has free draining soil, gets plenty of sunshine and is sheltered from winds.

Allium bulbs

When you plant the bulbs, you need to plant them at a depth which is approximately 4 times the diameter of the bulb. If you have selected a smaller variety then plant them about 7.5 to 10cm apart. And for taller species you need to leave around 20cm between bulbs.

Should you plant your alliums in container then choose a deep pot and use a mix of John Innes No.3 peat free compost and some horticultural grit.

And before you wonder who John Innes is, he was a 19th century philanthropist who donated his fortune for the improvement of horticulture. There are 3 John Innes mixes that each do a slightly different job. No.1 is for young plants and cuttings, No.2 is potting on plants and vegetables, and No.3 is for mature plants grown in pots such as shrubs, conifers, trees, and perennials.

How long do Alliums take to germinate?

When you grow from seed, it takes around 12 weeks to germinate and then it will take several years for them to reach flowering size.

How do you grow Alliums and are they easy to grow?

Yes, alliums are easy to grow. Just make sure you plant them in best location, so they thrive. Plant your alliums in a…

  • Sheltered spot
  • With well-drained soil
  • And a sunny position

Plant them out in October or November and they should start to flower in May and June.

Let the allium foliage die down naturally, and don’t be tempted to cut the leaves off before they’ve died down, to allow them to produce food for the bulb to flower next year.

I recommend having some low-growing plants surrounding your alliums to disguise the foliage, and as it rots down it will boost the soil. I would keep the flower heads as they turn a bronze colour, as this adds interest over the winter.

Or you can let them dry out and transform them into decorative pieces, like I did.

How long do they live for?

All being well your healthy allium plants should live 5 years or more.

How big do they grow?

Taller varieties of alliums such as Allium giganteum and ‘Summer drummer’ can reach heights up to 1.82m (6ft tall). With smaller varieties like Allium moly, Allium neapolitanum, and Allium roseum grandiflorum, around 30cm tall.

Allium giganetum

How long do Alliums flower for?

All being well, you should enjoy around 3 weeks of flowering from your allium blooms. Though as the flowers fade, they will retain their ball or hemispherical-like shape, which makes them a striking addition to your borders.

Are Alliums good for bees?

Bees, bumblebees, and butterflies love alliums. They provide a great food source for pollinators. The rich shades of purple are ideal for bees as they see this colour extremely well.

Allium bees

Are they frost hardy?

Yes. Alliums are hardy and cope with temperatures as low as minus 10 degrees celsius. Just check the variety before planting and if required mulch the area through winter to help the bulb retain warmth within the soil.

What colours do Alliums come in?

Alliums are available in blue, white, yellow, and pink . But the most popular alliums are purple. Varieties such as ‘Purple Sensation’ are a joy to behold. The cornflower shades of blue presented by Allium caeruleum with its smaller globes are so lovely to see.

You can get yellow alliums such as Moly, with their small star-shaped flowers. There are many white options too, one example being the Allium ‘White Empress,’ which works well in any scheme for a delicate and romantic feel. Pink Alliums range from pale to rich pink. The Allium ‘Pink Jewel’ is a wonderful example of a rosy, hemispherical variety.

Pink allium
Yellow allium
Purple allium
White allium
Blue allium

When do they flower?

Alliums planted in October will give the longest flowering time. You will see your allium bloom between late spring and early summer, the flowers lasting 2-4 weeks depending on the variety. This makes them a wonderful choice for garden colour in the interval between seasons.

Do Alliums flower in the first year?

Yes, as a perennial plant, they will come back every year.

Do Alliums need a lot of water?

Alliums are drought-tolerant and resilient.  If your Alliums are in the ground, regular watering is necessary when in bloom, but be mindful of watering after your Allium flowers, to avoid bulb rot.  Those Alliums grown within containers will need more watering during flowering, but make sure the drainage in the pot is good to avoid waterlogging.

Do they need staking?

Alliums offer surprisingly strong stems to hold their lollipop heads, however, they may need staking if you live in an area with strong winds or if you are growing particularly tall varieties, but I am confident their strong stems will support them when planted in a sheltered position.

Alliums standing tall without support

Do Alliums need deadheading?

Deadheading once the flowers have faded prevents your Alliums going to seed. I prefer to leave them as they offer interest in the border from late summer, and I cut them to create indoor Christmas decorations, to use in a wildlife hotel or bringing them in the house to add bold style. Deadheading offers no benefit to the plant but if you do deadhead the allium, then use a pair of clean and sharp secateurs.

Do Alliums need feeding?

Apply feed early in the spring when they are actively growing and preferably before blooming. A granular all-purpose fertiliser is good choice. You can also apply an eggshelll feed, using crushed eggshells and water. Steep the shells for a few days and it will supply calcium, which is essential for bulb development. If you want to apply a liquid feed, it will offer a fast-acting option as the feed is absorbed by the plant as it draws water. Mulching and regular watering will complement your feeding routine.

Do they change colour?

No, though if you are looking for flowers that change colour I would recommend Hydrangeas. These shrubs are known for their ability to change colour based on the type of soil they grown in.  Acidic soil will give you blue flowers and alkaline soil will give you pink ones.

Will they flower twice?

These lollipop flowers only flower once but, as perennials, will reappear the following year.

What do you plant with Alliums?

Plant alongside other perennials like Echinacea as this will hide the dying foliage of your Allium. Peonies is another statement plant which your Alliums can use for support in exposed areas.  Euphorbia, Salvia and Verbascum will also add more interest.


What not to plant near Alliums?

As a member of the onion family, though not edible, you might think to plant Alliums amongst your peas, beans, and asparagus. But there are reasons not to do this.

For the legumes (peas and beans) the natural antibacterial properties of alliums inhibit the nitrogen-fixing bacteria that legumes need to grow.

And as alliums grow underground this can disturb the shallow roots of asparagus crowns, making it challenging for them to grow.

When do you plant Alliums?

You can plant them at the same time as Spring flowering daffodils, tulips, and hyacinths.  Early to mid-Autumn is recommended but the optimum time is October and later only affects the blooming time resulting in a slightly shorter period and sometimes a slightly shorter length flower stalk.

Do they multiply?

You can plant them at the same time as Spring flowering daffodils, tulips, and hyacinths.  Early to mid-Autumn is recommended but the optimum time is October and later only affects the blooming time resulting in a slightly shorter period and sometimes a slightly shorter length flower stalk.

When can I move Alliums?

Wait for foliage to die back as they produce the energy for next year’s growth. In late Autumn or very early Spring, lift the bulbs and replant immediately at the same depth in a new location. If in doubt, smaller growing alliums are 7.5 – 10 cm and taller alliums like the giant varieties are around 20 cm.  A great tip is a depth of 2.5 times the current bulb size.

What to do with Allium offsets when moving?

These are new young bulbs attached to the mother bulb, and when moving your Alliums you can detach the offsets and plant them directly in their final positions or grow on in pots. These offsets develop into flowering bulbs much quicker than when grown from seed.

Soaking seeds

Do they make great cut flowers?

Yes, they make excellent cut flowers thanks to their stiff stems and being very long lasting.  Immerse them in water as soon as you make the cut, changing water frequently, cutting stems by 3 cm every water change. Give them a little liquid food too and you will guarantee success. Purple Sensation is a good option for cut flowers. Why not create a cut flower border to keep you cropping all season.

Alliums growing in a vase

When do Alliums stop flowering?

Most Alliums finish flower in early summer, so create a border that will offer successional flowering, by adding something like Echinacea to flower from June, and Agapanthus that will offer showy flowers in June, July and August.

What time of year do you collect Allium seeds?

When the heads are dry and you see black seeds left, shake them into a paper bag and pop into an airtight tic-tac box storage.  If you leave this too late the wind will blow the seeds away.

How do I know when my Allium seeds are ready to harvest?

In late summer when the heads are dry and brown in colour. Remember, growing Alliums from seed can take several years to flower so you need a lot of patience!

Faded allium flowerhead

When do Alliums die off (back)?

Late summer after flowering the energy starts to go back into the bulb.  The unique structure allows them to store food to carry them over Autumn and Winter until the environmental conditions are favourable to help initiate growth. It is a plant with an enlarged underground storage organ with incredible energy.

When to cut down Alliums?

Cut them back when the stalk and flower head is completely brown and dry.  You know then that the energy has gone back into the bulb for next years growth.

When do they start to grow back?

You can expect your Alliums to reemerge from their bulbs each spring, with flowering starting for many varieties in May.

Can you divide Alliums?

Alliums last many years and will need to be divided every 3 – 4 years.

Will Alliums spread?

Yes, most varieties are clump-forming perennials which may also self-seed in the border. This allows you to increase your allium yield if you look after them properly.

If you want to limit their spread, dig up and divide the bulb clumps and remove any self-seeded individual bulbs if they’re overcrowding your flower border. Perhaps you could gift surplus plants to some green-fingered friends or family members.

What are the common problems with Alliums and how do I fix them?

Ornamental alliums are typically relatively problem free. There are challenges that affect the onion family, but if you keep the ornamental and the edible plants apart this negates most of these from happening. But here are a few things to keep a look out for:

Onion fly damage

Onion fly

It is the maggots of this insect (they look like a grey house fly) that do the most damage as they eat the roots. If this happens you may see yellowing leaves, or the plant will fail all together.

Downy mildew damage

Downy mildew

This occurs during mild, humid weather. Yellow, brown or pale green blotches will appear on the leaves with what looks like mould on the underside. You may also find that leaves will wilt and die from the tip downwards.

To reduce the risk of this, avoid planting too close together, and divide congested clumps. Make sure that plants in the area you are growing have good air flow, keep on top of division, and don’t water too much. You can also remove and dispose of affected leaves but do not put them in your compost pile.

Allium leaf miner

Allium leaf miner

Both the insect and offspring cause damage to the alliums. The female fly will puncture and feed from the leaves leaving very distinctive lines of white dots on the foliage, whilst its larvae tunnel into the leaves, stems and bulbs. You may see the allium display distorted or twisted leaves. The insects themselves are very small about 3mm in size.

Onion white rot

A fungal disease which impacts the bulb. Yellow, wilting leaves are the first signs above ground, but check the bulb below the ground for confirmation of this fungus. If this is the cause, it will show white, fluffy, fungal growth at the base. Dispose of the bulbs in the green waste bin and not your compost heap, and avoid planting any alliums in the affected area. The damaging fungal spores can remain in the soil for at least 15 years.

How do I stop slugs and snails from eating my Alliums?

The other common pest to keep an eye out for are our old friends the slug and snail. Now they do have an important part to play in the ecosystem, but we want them to be focussed materials we don’t want, rather than our prize blooms.

The best things to do include:

  • Avoid watering at night.
  • Encourage birds into the garden.
  • Use grit or crushed eggshells to create a barrier that is uncomfortable to travel over.
  • Use copper tape around your pots and containers.
  • Plant a beer trap – not too much, just enough to attract them, and sit the trap just proud of the soil so beneficial insects such as ground beetles don’t fall into it.

Why are my Alliums drooping?

This can be related to over or underwatering. Despite alliums being drought tolerant they still need watering during very dry spells and more so if they are in pots and containers.  If you think you have overwatered perhaps the soil or compost is waterlogged.

My rule is if the soil is moist no need to water them, just apply a balanced fertiliser to assist in the early stages of growth.  Alliums also need sunlight and if they are in excessive shade, they will keep reaching for more light, which can make the stems stretch, weakening them which can be responsible for drooping.

Why do my Alliums have yellow-tipped leaves?

Not enough nitrogen can cause yellow tips, as can some diseases such as onion white rot and downy mildew. Yellowing at the bottom of the leaves can indicate too much heat and not enough water BUT yellowing is not always a sign of problems and can be part of the natural life cycle of the plant especially if you are reaching the end of the flowering period.

It could also be caused by water management if yellowing before the time of blooming, or deficiencies such as lack of nutrients before blooming.  I like to plant Alliums at the mid to back of my border so smaller shrubs hide the yellowing leaves as the lifecycle initiates.

Are they poisonous to humans?

They aren’t generally toxic to humans, but as ornamentals bulbs, they are not grown with the intention of eating them, so I suggest you avoid doing so.

Are Alliums poisonous to pets?

Unfortunately, the chemicals within alliums are toxic to cats and dogs. So, if your pet digs in the garden then please don’t plant them.

The lovely pompom blooms of Alliums create wonderful interest in garden borders. If you have any questions about this or any other plants you want me to do a video on, please subscribe to my YouTube channel and leave a comment below one of my Google Questions videos.

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