When to Plant Allium Bulbs

Allium bulbs should be planted in the autumn, from mid-September to early November in the UK. This gives them time to establish roots before winter while staying dormant until spring. Alliums are hardy and thrive in cold conditions once planted, so even late autumn planting is suitable—just ensure the ground isn't frozen or waterlogged.

When and How to Plant Allium Bulbs

Plant allium bulbs in full sun and well-drained soil. Dig a hole about three times as deep as the bulb is tall—generally around 10 to 15cm for most types. Space bulbs at least twice their width apart to prevent overcrowding. Place the bulb in the hole with the pointed end facing up, cover with soil, and water well after planting. Raised beds or sandy soil are ideal, as alliums dislike wet roots.

Why Plant Allium Bulbs in Autumn

Autumn planting allows alliums to develop strong root systems before winter sets in. The cool, moist conditions are perfect for root growth, which helps the plants get off to a strong start in spring. They then stay dormant through winter and emerge with dramatic flower heads in late spring to early summer.

Benefits of Planting Alliums

Alliums offer bold, architectural interest and are loved by pollinators. Their tall stems and globe-like blooms add structure to borders and contrast well with softer planting. They’re also deer- and rabbit-resistant, low-maintenance, and can thrive in poor soils. Once established, they multiply over the years and are ideal for naturalising.

When to Expect Growth

After autumn planting, alliums begin root growth but won’t show visible foliage until early spring. Flowering typically occurs from May to June, depending on the variety. Once flowering ends, the seed heads can be left for visual interest or collected for dried arrangements.

Instructions

Choose a sunny spot with well-drained soil. If your garden is heavy clay, improve it with grit or organic matter to avoid rot. Plant the bulbs with the flat side down and pointed end up. After covering with soil, water in lightly unless rain is due. Avoid planting in shallow or soggy soil—this leads to failed growth or bulb rot over winter.

Caring for Alliums After Planting

Alliums require little care once planted. They dislike waterlogged soil, so avoid overwatering. During dry spells in spring, a light watering helps bud development. There’s no need to feed unless your soil is very poor—then a low-nitrogen fertiliser in spring can help. Once flowers fade, leave the foliage until it yellows and dies back naturally.

Should You Deadhead Alliums?

Deadheading isn’t essential, but removing spent blooms can neaten the display and prevent self-seeding if that’s not desired. However, many gardeners leave the seed heads for their ornamental value. They add structure and look striking in dried arrangements or left standing in the garden.

What Happens If You Plant Alliums Too Late?

If allium bulbs are planted too late—after the ground is cold and wet—they may rot before rooting. Even so, it’s worth planting them late rather than storing them. If you've missed the ideal window, plant as soon as possible. Never wait until spring—spring planting doesn’t give them time to establish, and you’re unlikely to get flowers.