Best method for planting alliums so they return ‘spring after spring’

Frances Tophill on how to look after alliums

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Alliums are hardy bulbs that can tolerate most soil conditions, making them very easy to grow from scratch in your garden. These striking flowers can be planted directly outdoors right now too, with plenty of time left to get them growing before autumn comes to an end. According to Sarah Raven, alliums will “magically return spring after spring” if planted correctly, and it’s very easy to get right.

How to plant alliums

Alliums are from the onion family which includes many familiar edible plants such as leeks and garlic, as well as attractive flowering types.

These ornamental varieties are a great addition to the garden, with their showy flowerheads making for an unbeatable pop of colour from spring through to the end of summer.

While the blue, purple, white, and pink petals require little effort to grow, there’s one key step that can make your floral display even better.

Plant in clusters or “drifts”

Spring and summer flowering bulbs are usually planted individually into beds and borders, though British gardener and author Sarah Raven advised against it while planting alliums.

She explained that one hole for each bulb works for a “dotty look”, though it is best to dig a trench to grow “good drifts” of alliums outdoors instead.

If you do want a more spaced-out display, plant bulbs in groups of two’s or three’s to allow the swathes of “sparkler heads” to really stand out.

While spacing is crucial to maximising the impact of these striking ornamental plants, soil conditions and planting depth are also key to growing a successful show of garden blooms.

Allium bulbs can be planted directly outdoors in September, October, and November, or indoors in January.

According to Sarah Raven, alliums will do best in heavy soil, with a two-inch layer of grit spread over the bottom of each planting hole or trench.

As a general rule, the hole should always be planted to at least twice the depth of the bulb, with a gap of at least three times the bulb width between each bulb or cluster.

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Leave enough space between each bulb

The best way to determine the planting depth of each bulb is to roughly measure each one based on the size.

However, there are a few guidelines you can follow to suit different types of alliums.

Sarah Raven said: “For small and medium-sized bulbs such as Purple Sensation, this is around 10-15cm deep and 10-15cm apart.

“For the larger varieties such as Purple Rain, it’s around 15cm deep, but at least 20-30cm apart as they need more space for their much larger flower heads and foliage.

“Giants like ‘Globemaster’ need to be 30-45cm part to accommodate their gorgeous heads.”

How to plant alliums in pots

Allium bulbs will grow well in both open soil and pots, but it is important to use good quality compost for the best results.

Sarah Raven recommended a “nice deep pot” to allow the strong, tall stems to thrive and support the striking globe-shaped flowerheads.

While it is always best to plant potted alliums at the same depth as ground-grown blooms, it may not always be possible with larger varieties.

In this case, you should try to plant each bulb with at least 4cm of compost beneath it, and plenty of space around each one to grow.

Finish by top-dressing the pot with a generous layer of grit to enrich the planting site.

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