Valued for their firework displays that supersede the cacophony of tulips, alliums have rightly become a stalwart of the garden and a familiar addition to our borders in late spring. Not only are their flowers rich in nectar and attractive to bees and other pollinators, but the spherical inflorescences add colour and architectural form to borders when in flower, and their intricate dried seedheads persist through to autumn. Now, thanks to continued breeding and recent introductions, there are new cultivars of these attention-grabbing blooms that arrive a little later to the party, and we can enjoy alliums in our gardens all summer long.
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Most alliums prefer a spot in full sun in reasonable, free-draining soil but some, including Allium angulosum and Allium nutans, will take richer conditions and a little shade, while Allium ursinum (wild garlic) thrives in deep woodland. All alliums generally fit into one of two groups: those that are bulbous and have a resting dormant period after flowering; and those that are clump forming, growing through spring and summer with persistent foliage.
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- How to grow summer-flowering alliums
- When to divide summer-flowering alliums
- When to plant summer-flowering alliums
- The best summer-flowering alliums to grow
- Where to buy summer-flowering alliums
How to grow summer-flowering alliums
Alliums are relatively easy to look after and can be reliably perennial if grown correctly. They perform best in free-draining conditions, as they dislike sitting wet in winter and during their summer dormant period, so avoid heavier clay soils. National Collection holder Jackie Currie recommends lifting the fussier varieties, such as Allium atropurpureum, allowing them to dry and bake as they would in nature, before replanting early autumn, to ensure a good display.
For the clump-forming types, it’s best to treat them like a herbaceous perennial, buying container-grown stock and planting in spring or late summer to a depth where the surface of the soil matches that of the potted plant. You may find some suppliers send them out as bareroot plants in early spring, which can be quite good value. These should be planted or potted immediately on arrival to a depth where the pale bulbous section sits below the soil surface, with only the newly emerging leaf tips visible.
When to divide summer flowering alliums
In time, clumps may become congested. These should be lifted and divided. For bulbous types this is best done in summer after flowering. Use a border fork to carefully lift and dislodge the bulbs, selecting and replanting the biggest and relocating any leftovers. Herbaceous types tend to be happier as dense clumps, though you can lift and divide in spring and late summer if needed. Simply dig up the entire clump, before using a couple of forks to gently split into smaller sections, before replanting or potting.
Some alliums are vigorous self-seeders or multiplying with the production of bulbils that are produced in the soil or in the centre of the flower. Generally, only a handful of the bulbous ornamental types and culinary varieties, such as chives, are a problem. Prompt deadheading after flowering, before the seeds are ripe and have dispersed, will help ease the problem.
When and how to plant summer flowering alliums
For bulbous types, plant dried bulbs soon after purchase in late summer or autumn to a depth of approximately three times the height of the bulb.
Alliums a can be grown in containers. Good drainage is key and they’re best grown in a soil-based compost such as John Innes No.3.
Summer-flowering allium pests
Ornamental onions are generally pest and disease free. Fungal diseases, such as mildews and rusts, can be a problem, more so on edibles grown close together. Removing affected foliage and improving growing conditions will help. Their strong taste makes them less desirable to deer, rabbits, slugs, mice and pigeons.
How tall are summer-flowering alliums
They range in height from 25cm to around 90cm, making them well suited for the smaller garden or at the front of the border, as well as in containers. They also work well in gravel gardens and naturalistic plantings, where Allium senescens subsp. glaucum will appreciate the drier conditions. In contrast, Allium angulosum and Allium nutans will sit happily below a rose in a lightly shaded spot.
What to plant with summer-flowering alliums
When pairing them with other plants, it’s best to select plants that are also well behaved and won’t smother them. In a cottage-garden-style setting, you could include summer-flowering Calamintha nepeta ‘Blue Cloud’, Origanum ‘Rosenkuppel’, Nepeta racemosa ‘Amelia’ and contrasting Hylotelephium ‘Red Cauli’, along with some of the small lighter salvias such as Salvia ‘Nachtvlinder’ or Salvia ‘Blue Note’.
For a more natural look, plant medium-to-large varieties alongside well-behaved ornamental grasses such as Miscanthus nepalensis, Molinia caerulea ‘Moorhexe’ or Panicum virgatum ‘Shenandoah’, including the lovely white umbels of Ligustrum lucidum, zesty Euphorbia seguieriana and Serratula tinctoria var. seoanei, perhaps with Phlox x arendsii ‘Hesperis’ and Symphyotrichum ‘Little Carlow’ for additional late colour. At the front of a hot, sunny border, the smaller varieties will sit well alongside bearded irises, Origanum ‘Bristol Cross’ and Verbena officinalis ‘Bampton’.
Summer-flowering alliums in brief: fact file
What Allium is a genus of more than 1,000 species that include cultivated onion, garlic, shallots, leeks and chives. The summer-flowering species featured here are largely ornamental plants, sometimes known as ornamental onions.
Season June to late August. Size Heights vary from 5cm to 2.2m. All heights and spreads given here are approximate. Conditions Sunny to light shade in free-draining loam.
Origins Throughout North America, Europe, Asia and parts of northern and southern Africa.
Hardiness Hardy throughout the UK and suitable for gardens in USDA zones 4a to 8b. *Holds an Award of Garden Merit from the Royal Horticultural Society. †Hardiness ratings given where available .
The best summer-flowering alliums to grow
Allium angulosum ‘Summer Beauty’
Numerous spherical clusters of soft lavender-pink flowers appear elegantly on thin stems above lush strappy mid-green leaves throughout summer, from July to August. Clump- forming type. Height and spread: 45cm x 25cm. RHS H6, USDA 5a-8b†.
Allium ‘Millennium’
A great selection that offers tight rose-purple flowers during July and August. These are held in attractive pompoms over healthy bottle-green foliage that remains throughout summer. Clump-forming type. 90cm x 15cm. RHS H6, USDA 5a-8b.
Allium atropurpureum
A species that produces possibly the darkest flowerheads of any allium, with flat-bottomed spheres of sumptuous blackcurrant-purple stars held openly on sturdy stems from mid-June to July. Bulbous type. 40cm x 5cm. RHS H5.
Allium sphaerocephalon
The classic drumstick allium with tight heads of dark-purple flowers held on tall, upright, thin stems with fine foliage, flowering from June to July and into August. Bulbous type. 90cm x 15cm. AGM*. RHS H6, USDA 4a-8b.
Allium pskemense
A rare allium, thought to be closely related to the cooking onion, with fresh spheres of greenish-white flowers from June to August. Its sturdy tubular stems stand high above glaucous green foliage. Bulbous type. 80cm x 30cm. RHS H6.
Allium tuberosum
Garlic chives are an attractive edible plant that work well in ornamental plantings, with small white star-shaped flowers appearing numerously over the thin green leaves through July to September. Clump-forming type. 45cm x 30cm. RHS H5.
Allium thunbergii ‘Ozawa’
One of the latest-flowering alliums with deep lilac- pink flowers that open from globular buds in autumn and are held loosely on thin stems above grass-like foliage. Clump-forming type. 90cm x 15cm. RHS H5.
Allium senescens subsp. glaucum
A charming species with soft purplish-pink flowers from May to August, held high above a tight nestof silvery-green, grass-like foliage. Clump-forming type. 25cm x 25cm.
RHS H6.
Allium angulosum
Numerous spherical clusters of soft lavender- pink flowers appear from paler buds from July to August, elegantly held on thin stems above elongated mid-green leaves. Clump- forming type. 45cm x 25cm. RHS H6.
Allium amethystinum ‘Red Mohican’
A taller cultivar with maroon-purple-coloured flowers that sit tight in a cluster, with a characteristic tuft on the top giving this plant its name. Bulbous type. 1m x 20cm. RHS H5.
Allium vineale ‘Hair’
Unusual hair-like extensions grow from a purple centre during July, held on tall thin stems. Great for cut flowers and as a novelty, though bulbils form in the flower making it good at colonising gardens. Bulbous type. 65cm x 10cm. RHS H5.
Allium flavum
Loose hanging clusters of citrus-yellow flowers appear from May to July, contrasting beautifully with the glaucous, grass- like foliage below. One for a naturalistic gravel area. Bulbous type. 40cm x 5cm. AGM. RHS H5, USDA 6a-8b.
Where to see and buy summer-flowering alliums
- Jackie Currie 11 Oak Close, Chiddingfold, Surrey GU8 4SA. National Collection holder; opens garden by appointment. plantheritage.org.uk
- Cotswold Garden Flowers Sands Lane, Badsey, Evesham, Worcestershire WR11 7EZ. Tel 01386 833849, cotswoldgardenflowers.co.uk
- Kevock Garden Plants Kevock Road, Lasswade, Midlothian EH18 1HX. Tel 0131 454 0660, kevockgarden.co.uk
- WS Warmenhoven A Dutch family nursery specialising in alliums. Mail order only. warmenhoven.co.uk
