Blue globe onion

Blue globe onion: how do you recognise it?

Habit

Thin, stiff stems of 40–50 cm above a few leaves; barely 10 cm wide.

Leaves

Two to four narrow, grass-like leaves that wither around flowering time.

Flowers

Dense, round heads of 2.5–4 cm packed with star-shaped, sky-blue flowers, in June–July.

Fruit

Small capsules with black seeds; sometimes tiny bulbils also form among the flowers.

Bulb

Small, 1–2 cm; planting depth 8–10 cm.

Flowering: June–July · Plants: September–November

Why grow it?

• A rare, clear sky blue in June–July, a colour few bulbs can offer.
• Bees and butterflies visit the flowers.
• Takes up almost no space: you can tuck it in anywhere among perennials and grasses.
• A charming cut flower for small posies.
• Very hardy and easy on dry, sunny soil.

Blue globe onion: where does it grow best?

• Full sun.
• Free-draining sandy or loamy soil, neutral to chalky.
• Dry to normally moist: in wet winters the bulbs rot. Mix grit into heavier soil.
• Plant in groups of at least twenty, 5–8 cm apart, among low grasses or perennials that hide the dying leaves.

Light

Sun

Soil type

Sand or loam

Acidity

Neutral or chalky

Moisture

Dry or normal

Size

0.5 m tall, 0.1 m wide

Hardiness

Hardy (to -25 °C)

Goes well with

• Feather grass: Fine, swaying stems among which the blue globes seem to float.
• Blue fescue: Low, blue-grey tufts that hide the dying leaves.
• Sun rose: Low yellow flowers in the same dry, sunny spot.
• Yarrow: Flat yellow heads beside the blue globes, also loved by butterflies.

Blue globe onion: when and how to plant it?

Plant in September–November.

1. Plant the bulbs in September–November, as long as the soil is not frozen.
2. Dig a wide, shallow pit 8–10 cm deep, so you can plant a whole group at once.
3. Set the bulbs pointed end up, 5–8 cm apart, in groups of at least twenty.
4. On heavier soil, put a layer of grit in the bottom of the pit.
5. Cover with soil and firm lightly; water only if the soil is bone dry.
6. Keep the bulbs out of reach of children and pets before planting.

Care

Watering

Rarely needed; only in a very dry spring.

Feeding

Not needed; on poor sandy soil a little compost in March is enough.

Leaves

Let the leaves die back naturally after flowering, so the bulbs can store food.

Deadheading

Leave the heads if you want it to self-seed a little, or cut them off.

Cutting

Cut the stems when half the flowers are open and change the water often.

Tip: Plant in groups of at least twenty bulbs among low grasses: only in a group does the blue really come into its own.

Blue globe onion: when to prune it?

When: No pruning is needed. After flowering you can cut off the spent stems; always let the leaves die back naturally.

How:

• Cut off spent stems or leave the dry heads standing.
• Only remove the leaves once they are completely yellow or brown.
• In late summer, simply pull the dry stems out of the ground.

Caution: Do not cut the leaves while still green: the bulbs weaken and flower less.

Pruning calendar and basic rules

Propagation

Offsets

After a few years the bulbs form offsets. Lift the clump once the leaves have died back, separate them and replant in autumn.

Bulbils from the flower head

If tiny bulbils appear among the flowers, pick them in summer and plant them shallowly in a pot or in the border.

Seed

Sow ripe seed in autumn in a pot left outdoors. Seedlings flower after 2–3 years.

Blue globe onion: how does it get through the winter?

Hardy to −25 °C.

• Very hardy, to about −25 °C: in Belgium the bulbs simply stay in the ground.
• Wet soil is the biggest danger: plant in a free-draining spot or mix grit into the soil.
• In a pot: stand it against a wall in winter, out of the rain.

Diseases and pests

• Bulb rot: Bulbs that fail to come up or are soft in wet soil. Plant them in a drier spot or in gravel.
• Yellow leaves at flowering: Normal for ornamental onions. Hide the leaves among low grasses and let them die back.
• Slugs: They eat the young leaves in spring. Pick them off in the evening.
• Fewer and fewer flowers: The group is too crowded or too shady. Lift the bulbs once the leaves have died back and replant them more widely spaced, in sun.

Through the year

• March: Leaves emerge. Compost on poor soil.
• April: Watch for slugs.
• May: Flower buds appear.
• June: Flowering begins. Cut stems for a vase.
• July: Flowering. The leaves die back. Pick bulbils.
• August: If needed, lift and separate crowded groups.
• September: Plant bulbs.
• October: Plant bulbs. Sow in a pot outdoors.
• November: Plant the last bulbs.

Edible and useful

Not edible. Ornamental onions are true alliums, related to onion, garlic, leek and chives, and like them they are poisonous to dogs and cats: all parts, especially the bulbs, contain sulphur compounds that damage the red blood cells and can cause anaemia. Cats are more sensitive than dogs, and the signs (lethargy, pale gums, red or brown urine) sometimes appear only after a few days. Horses, sheep and other livestock can fall ill from them too. Even though the leaves and bulbs smell of onion, they are not grown as vegetables: do not eat them, and never store the bulbs with the kitchen onions, as they are not meant for eating and may have been treated with pesticides. Do not plant them where your dog digs, keep loose bulbs out of reach of pets and children, and do not put a vase of alliums where your cat chews the stems. If your dog or cat has eaten a bulb or leaves, call your vet, even if it shows no signs yet. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• Caeruleum means sky blue: a pure blue is rare among ornamental onions.
• In the wild it grows on the steppes of Central Asia, with hot, dry summers and harsh winters: that is why it copes so well with frost and drought.
• Ornamental onions are related to onion, garlic and chives, and they too smell of onion when you bruise a leaf.