How to Grow Allium Bulbs

11/06/25

Written By Susie Curtis

Allium flowers add texture and colour that improve any style of garden. These architectural flowers are perfect for punctuating borders and cut flower displays, but if you’re wondering how or when to plant allium bulbs, Johnsons is here to help. In this guide, we will cover the essentials of how to grow allium bulbs, going step by step through everything you need to know to bring these delightful globes of colour to your garden.

Why Grow Alliums in Your Garden?

Alliums bring beautiful bursts of colour to a display, but they also come with a range of tangible benefits to your garden:

Pollinator-friendly: Alliums attract bees and butterflies, turning your garden into a haven for pollinators and the ecosystems that depend on them.
Deer/rodent resistant: Thanks to their pungent scent, alliums deter the animals that would otherwise munch through your garden, protecting your blooms in the long term.
Drought-tolerant: No longer let the weather dictate the vivacity of your garden thanks to alliums' ability to go long periods without water once planted in the ground.
Great for cut flowers: The powerful colour of alliums makes them an ideal addition to your cut flower garden.

When to Plant Allium Bulbs

The best time to plant allium bulbs in the UK is in the autumn, from September to November. This is because the soil is still warm enough to encourage root development, but the autumn brings cooler temperatures that stop early shooting and higher rainfall ensures the bulbs have enough moisture to get them growing. Getting bulbs established in autumn allows them plenty of time to grow before the springtime bloom.

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How to Grow Allium Bulbs: A Step-by-Step Guide

Over our years of experience growing and caring for allium bulbs, we’ve identified the steps needed to grow healthy, beautiful alliums:

Step 1 - Choose the Perfect Spot: Find a space in your garden that receives full sun and has well-drained soil. These conditions are vital for healthy allium growth. The majority of bulbs will rot if they sit in waterlogged conditions, so ensuring good drainage is key.
Step 2 - Prepare the soil: Before planting, we’ve found that adding grit to your soil aids drainage, while providing compost supports with nutrition.
Step 3 - Planting Your Bulbs: There are two critical things to consider at this stage. The first is spacing, as you must ensure that your allium bulbs are at least 7.5 cm/3 in. apart (or 20 cm/8 in. for taller alliums). The second is the planting technique, as your bulbs need to be planted to a depth of three times the height of the bulb. Remember to plant them with the pointed end up!
Step 4 - Watering: Water your bulbs initially after planting, but note that allium bulbs are drought-tolerant and can therefore grow without additional watering. The Autumn and Winter rain should suffice.

Growing Alliums in Pots

Alliums are versatile in their beauty, looking amazing in pots as well as in your garden. For planting and growing your allium bulbs in pots, we have a few tips and tricks:

Pot Size: Allium bulbs prefer deep pots, and drainage holes are a must. We recommend a pot of about 45 cm/18 in. in size.
Compost Mix: General-purpose, peat-free compost works perfectly for growing allium bulbs, though we also recommend adding 20% horticultural grit to support healthy drainage.
Watering regime: Water regularly after potting; however, be wary of the compost becoming waterlogged. Keep an eye on drainage to guarantee healthy growth and prevent rot.

Allium Siculum Nectaroscordum Flower Bulbs

How to Look After Alliums

In our years of growing healthy and beautiful alliums at Johnsons, we’ve found that knowing how to look after allium bulbs is about much more than watering and waiting. Here are our essential expert tips:

Watering & Feeding

As we mentioned earlier, allium bulbs are drought-tolerant, meaning they can go without additional watering for quite a while. However, we suggest watering your alliums during prolonged dry spells that may occur during the spring, just to ensure they stay hydrated during their blooming weeks. We also advise that you support growth with high-potassium feed, as this supports bud and bloom strength.

What to Do With the Leaves

It can’t be overstated how important it is not to pick off your alliums’ leaves! Leaves start to look untidy before flowering, and by leaving them, you can supply next year’s bulb with a source of feed. If you don’t like the look of the leaves in your garden, we suggest companion plants like geraniums to hide the foliage.

After Flowering

Once your allium has successfully bloomed, leave the seed heads. Your garden will benefit from the architectural structure they sustain during the colder months. However, if you do want to get rid of them, they can also be deadheaded.

Do Alliums Come Back Every Year?

If you’ve successfully planted and grown your allium bulbs, you may be hoping they come back next year. Well, we’ve got good news for you, because alliums are certainly perennial, returning each spring thanks to the beautiful process of naturalising. This term refers to the way in which alliums and plants like them spread and multiply over time, creating naturalistic swathes of colour throughout your garden.

Expert's Choice: Top Allium Varieties from Johnsons Seeds

Can’t decide which allium bulbs to go for? Here are our top Johnsons Seeds picks for the perfect alliums to transform your garden!

For an intoxicating pop of blue, we can’t think of a better option than Allium caeruleum. With its densely packed, azure blue flower heads, this bulb complements a range of summer perennials.

Does your garden need a little bit of glam rock? Look no further than Allium cristophii, an almost avant-garde member of the Allium family. With its spiky, star-shaped flowers, this Allium species glistens in metallic lilac, flowering late and lasting a long time. It also looks fantastic when kept for Christmas decorations!

Imagine a tiny globe of bright pink brilliance, and you’ve got Allium sphaerocephalon. Its egg-shaped flower head opens from the top downward, revealing sensational dark-pink flowers that bring something different to any gardening scheme.

Troubleshooting Common Problems

Got a question or concern about your allium bulbs? Fear not, because we’ve got you covered with our quick-fire answers!

Yellowing Leaves: Don’t worry, this is perfectly normal! This is just the bulb recouping energy in preparation for next year.
Bulbs Not Flowering: This is due to your bulb either not getting enough sun or being planted too shallow in its soil bed.
Wilting and Rot: This is likely due to onion white rot, a disease which affects alliums and, unfortunately, cannot be controlled.

Frequently Asked Questions (FAQs)

How deep should I plant allium bulbs?

A general rule to follow is that allium bulbs need to be planted at a depth of around three times their height, ensuring they have enough room to root with respect to their size.

Can I leave alliums in the ground all year?

Yes – allium bulbs are nice and hardy, meaning they can withstand the colder temperatures of winter. In fact, they rely on this dormant period for their perennial growth.

What can I plant with alliums to hide the foliage?

There is a range of options we suggest here, including varieties of hostas, astilbe, geranium, and alchemilla mollis.

Explore Our Allium Bulb Collection at Johnsons Seeds

With the knowledge provided in this guide, you are now ready to breathe colour and vibrance into your garden with our range of allium bulbs. Autumn planting, soil drainage, plenty of sun – these principles are your roadmap to a garden bursting with variety, and we know that in following them, you will soon be rewarded with the terrific springtime bloom.

Ready to create your own spectacular display? Explore our full range of high-quality allium bulbs and find the perfect varieties for your garden today.