Giant onion, simply magnificent flowers

This allium is a superb flower, with amazing ornamental floral scapes.

Short list of Giant onion facts

NameAllium giganteum
FamilyLiliaceae (lily family)
Type – perennial

Height – 8 to 40 inches (20 to 100 cm)
Exposure – full sun
Soil – ordinary

Flowering – May to July

Easy to grow, it is perfect in flower beds and also in pots or garden boxes to decorate either a terrace or a balcony.

Planting giant onion

Giant onion is planted in fall more or less 4 to 5 inches (10 to 12 cm) deep in light soil.

  • Giant onion loves high sun exposure.
  • Soil must be light and drain well, and poor soil is ok.

A good way to know how deep to plant it is to multiply the height of the bulb by 3. If it is 2 inches (5 cm) tall, plant at a depth of 6 inches (15 cm).

Pruning and caring for giant onion

Caring for giant onion is extremely easy, since the needs of this perennial bulb plant are not complicated.

In both pots and in the ground, they will bear nice flowers without asking you to care for them.

  • Cut wilted flower scapes as they die off, cutting the stem off as short as you can.
  • Only cut leaves back when they have already turned yellow because that is when the bulb is stocking up on nutrients for the next blooming cycle.
  • No need to add fertilizer.

Note that giant onion leaves tend to turn yellow before or after the blooming of the large umbels, and so it helps to plant ground-covering perennials around the giant onion plants, to cover the wilted leaves and only let the flower stem stick out.

As for pot-growing giant onion, remember to water regularly because water needs are higher due to the fact that potted plants tend to dry off faster.

All there is to know about giant onion

A close-up of a giant onion flower, not yet fully open, with dark pink blooms.Giant onion is a perennial that grows quite easily and which will produce very beautiful purple blue flowers that can be up to 8 to 12 inches (20 to 30 cm) across.

Native to Europe and Asia, this ornamental onion belongs to the same genus as the following species: edible garlic, onion, shallot, chives and is in the same family as leek.

Giant onion varieties all boast superb flowers bunched up in balls and the size and color of this ball depends on the variety.

In flower beds or along edges, and also along a wall or simply plunked in the middle of the yard, the ornamental impact of this plant is guaranteed!

  • Allium giganteum, thanks to its tall bearing, is perfect to line the back of a flower bed.

It is also used in flower bouquets, because the foliage and the flowers both can be used to make appealing bouquets.

Smart tip about giant onion

For the taller species you can stake the stem to keep it from folding under the wind. Nice for this is to use bamboo, it is perfectly suited and actually enhances the visual impact of the plant.


Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Giant onion opening up shared by Michael Levine-Clark under © CC BY-NC-ND 2.0
Giant onion flower shared by Capri23auto under © CC0 1.0

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