Allium

Choose by flower-head size, plant height and color. Small alliums (about 20–30 cm) suit rockeries and containers; medium types (40–60 cm) fit mixed borders; tall types (80–120 cm) work at the back of beds and as cut flowers. For color, pick purples/blues for a strong focal point, white for contrast or a restrained palette, or a mixed selection for varied displays. Also consider bloom timing—Alliums flower in late spring to early summer—so plan companions to cover before and after their bloom.

Alliums prefer full sun and well-drained soil; avoid waterlogged locations that cause bulb rot. Plant bulbs at a depth of about two to three times their height. Space bulbs according to size: small 8–12 cm, medium 12–20 cm, large 20–30 cm apart so flower heads have room to show. If you have heavy clay, improve drainage or use raised beds or grit in the planting hole.

Plant in autumn before hard frost. Apply a balanced bulb feed at planting or a light fertilizer in early spring. After flowering deadhead the spent flower stalks to avoid unwanted self-seeding, but do not cut the leaves—allow foliage to yellow and wither before removing so the bulb stores energy for next year. Divide crowded clumps every few years after the foliage dies back.

Use their strong spherical flowerheads as architectural accents—group bulbs in odd numbers and layer small, medium and tall types for depth. Plant Alliums among lower perennials or groundcovers to hide dying foliage. They work well in borders, containers and as cut or dried flowers. As a bonus, their onion-scent makes them less attractive to deer and many pests.