Giant onion is a superb flower, with amazing ornamental floral scapes.
Short list of Giant onion facts
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).
- Proceed to group 10 or 15 bulbs close together to create clustered spots of color.
- Plant bulbs more or less 8 inches (20 cm) apart.
- Refer to our guidelines on planting bulbs
- Learn how to plant bulbs in clay or flooded soil
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
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 by Michael Levine-Clark under © CC BY-NC-ND 2.0
Flowering Giant onion by Ralph Nowack under Pixabay license