With their classic, plump flower heads, which seem to hover like purple clouds above other plants, alliums are one of the highlights of the summer garden. You might be surprised at the range of flower shapes and colours available among these ornamental onions – bright blue, white, gold, darkest purple and pale pink hues, as well as pendulous flowers, flat blooms and enormous flower heads like fireworks.
How to grow alliums
Plant bulbs at 2½ times their own depth in autumn and space them about 8 inches (or 4 inches in the case of smaller bulbs such as A. triquetrum). Some alliums have rhizomes (underground stems) instead of bulbs – these are the ones that look more like spring onions than dry bulbs on arrival. Plant these in autumn just below the soil surface and 4 inches apart.
Alliums aren’t too fussy, but a sheltered spot with well-drained soil in full sun is their ideal position.
For impact, plant alliums in groups. Create a year-long display with spring bulbs and hellebore hybrids in spring that will die down to make way for late-flowering herbaceous perennials, such as Japanese anemones, that will hide any untidy allium leaves and provide colour once the alliums are over.
To keep alliums tidy, gather up the dead leaves in early summer and remove any stems that become detached at their bases in late summer. Although all on trial stood up well, in a very exposed site you may need to provide support for stems. Keep an eye out for rust and cut back diseased foliage. Alliums are hardy in Britain and can be left in the ground all year round.
Some of the most noteworthy ornamental alliums include:
- Ornamental garlic (A. aflatunense) – lovely lilac-colored, spring-blooming type.
- Giant onion (A. giganteum) – one of the largest blooming species, with globe-shaped flowers that grow up to 5 feet or more.
- Golden onion (A. moly) is beautiful, especially when placed in a rock garden. Its yellow, star-like flowers make an impressive sight in the garden when planted in drifts too.
- Bride’s onion (A. neapolitanum) – spring-blooming with star-shaped white flowers and narrow, green leaves.
- Rosy garlic (A. roseum) – with its sweet-scented pink blooms, this allium species is great for adding to beds and borders.
- Drumstick allium (A. sphaerocephalon) – these have reddish-purple globes and fit in nicely with companion plants like hosta. Their blooms, even once faded, still remain attractive throughout fall and winter.