10 of the best: top-performing alliums for late spring colour
Perennially popular alliums, also known as ornamental onions, are grown for their showy flower heads that bob pleasingly above the planting line in late spring and early summer. Available in a wide array of sizes and shades of blue, purple, white and even yellow, alliums are planted as bulbs in autumn (although some, such as Allium albidum, have rhizomes). However they can also be bought as containerised plants from garden centres in April.
Not just good for gardens – being favoured by bees and other important pollinators – alliums also make a striking cut flower; but be sure to change the water regularly to dull the onion scent. Even when dying back, the dried seed heads of alliums continue to provide sculptural interest, but the leaves can become unsightly so consider planting low-lying shrubs and flowers at their base, such as pheasant’s tail grass.
Between 2013 and 2016 the RHS trialled more than 100 allium varieties at RHS Garden Wisley, complementing its earlier trial of shorter rock garden alliums. Below are its pick of the statuesque stunners that have won the much-coveted Award of Garden Merit (AGM).
1. Allium hollandicum ‘Purple Sensation’
The small, vivid rosy-purple flowers form crowded spherical umbels. It is reliably perennial and combines well with grasses in a gravel border.
2. Allium cristophii
This vast ball of tiny star-shaped, rosy-violet flowers grows to 20cm wide and is a much-loved feature in borders. Flowers in late June leaving highly attractive seed heads for late summer interest.
3. Allium ‘Mount Everest’
Statuesque 'Everest' has a sturdy seed head and proved to be the best of the white alliums. Each globe is made up of 50 or more flowers with a green eye and it looks particularly striking in among its purple peers.
4. Allium ‘Globemaster’
This reliable long-flowering allium has deep violet flowers with a bright green stem. One of the top performers in the RHS trial, after several years the flowers are smaller but more numerous.
5. Allium jesdianum ‘Early Emperor’
One of the earliest to flower in May, ‘Early Emperor’ has a contained habit and deep purple, starry flowers that contrast with the white of the stamens.
6. Allium ‘Powder Puff’
Shorter than the majority of its peers, tennis-ball sized ‘Powder Puff’ is an ideal choice for patios or at the front of borders. Its name hints at its refined, delicate-looking flowers.
7. Allium ‘Purple Rain’
With a fast-growing habit, long-lasting flowers that increase in intensity and excellent seed heads, ‘Purple Rain’ was labelled the best in trial. Great for the back of borders and to follow on from ‘Purple Sensation’.
8. Allium sphaerocephalon
Later flowering than most – in July and August – this variety, commonly called ‘drumsticks’, is egg-shaped with dense heads of lime-green flowers. The flowers gradually turn crimson-maroon to reddish brown and are an old favourite for wilder borders and beds.
9. Allium flavum
Small, bell-shaped golden-yellow flowers cascade from the stem bearing a striking resemblance to the agapanthus. Clump-forming and grows to 40cm.
10. Allium caesium
Naturally inhabiting deserts and dry fields, the light blue A. caesium can be described as a miniature allium growing to just 1in (2cm) across. Its green-veined violet blue flowers add a splash of colour when planted en masse in beds and borders.
For more information about alliums or the Award of Garden Merit, visit rhs.org.uk
