Planting alliums

Where to plant Allium bulbs?

Apart from some edible species such as A. ursinum or wild garlic, which tolerate partial shade and the cool soils of woodland areas, these Mediterranean bulbs thrive in full sun. It is best to plant your alliums in a sheltered spot to protect their stems, especially for the taller varieties.

They appreciate all types of light soil, even poor, dry, or stony soils, as long as they are perfectly drained; they dislike heavy, waterlogged soils in winter, which can cause the bulbs to rot. They will thrive and rebloom for many years in well-drained soil but may only last a few years in compact, heavy, or clay soils.

Fully hardy, they can overwinter underground even in colder regions. Once well established, they will rebloom for many years.

They can be planted en masse or individually, in the middle or at the back of perennial or shrub borders, in edgings, rockeries, or in pots. Edible species such as garlic (Allium sativum), onion (Allium cepa), shallot, or chives (Allium schoenoprasum) are, of course, best reserved for the vegetable garden!

Think about post-flowering. In borders, plant alliums alongside various perennials such as Delphiniums, Eryngium, or ground-covering plants (Hardy Geraniums), which will take over the flowering display and hide their yellowing foliage. They also pair beautifully with ornamental grasses and with peonies and roses.

Alliums pair well with all kinds of perennials. Here, the grey tones of an Eryngium giganteum highlight the violet inflorescences of an Allium schubertii.

When to plant allium?

Allium bulbs are planted in autumn, from September onwards, when the soil is still warm. The ideal time to plant them is before the end of November, to allow them to establish strong roots before the onset of severe frosts. If you’ve “missed the boat”, don’t worry: you can still plant your alliums until the end of January, as long as the ground isn’t frozen. However, keep in mind that late planting may delay their flowering.

Which allium for which location?

Alliums comprise over 700 species and adapt to all types of gardens thanks to their great diversity. They vary in height, ranging from tall species, measuring between 80 cm and 1.50 m, to medium-sized species of 45 to 75 cm, and down to compact, low-growing species of 20 to 40 cm. Their flowers, in spherical or loose umbels, offer diameters ranging from 5 to 40 cm. This diversity allows them to be used to structure flower beds or adorn more intimate spaces such as borders or pots.

Structuring Flower Beds with Tall Alliums

Tall alliums, such as Allium christophii or Allium ‘Globemaster’, are perfect for the back of flower beds. Plant them in groups for a spectacular effect and pair them with low-growing perennials to create contrast and harmony.

Brightening Borders and Pots with Small Alliums

The most compact alliums, such as Allium moly, Allium karataviense, or Allium sikkimense, are ideal for borders, rockeries, or small spaces. Allium moly, with its bright yellow flowers, naturalises easily and is well-suited to wild areas or pathways. Allium karataviense, on the other hand, charms with its compact habit and ornamental foliage, perfect for pots or small flower beds.

Allium sikkimense, vigorous and perennial, is used in rockeries or borders

At what density should they be planted?

The planting density of alliums mainly depends on the size of the bulbs and the desired visual effect. If you’re aiming for a natural look, plant them in small, irregular groups. For a spectacular display, opt for dense planting in large numbers.

For a harmonious result, we recommend planting at least five bulbs of the same variety. Depending on the species and bulb size, plan for a density of 15 to 150 bulbs per m². Smaller bulbs, such as those of low-growing alliums, can be planted in greater quantities to cover a dense area. Conversely, large bulbs of tall alliums, like Allium giganteum, should be planted in groups of 4 to 10 bulbs, spaced about 10 cm apart.

When planting, ensure proper spacing and avoid letting the bulbs touch each other! They should be spaced at least half their width apart. Smaller bulbs can be planted very densely, spaced 5 cm apart, medium-sized bulbs 15-20 cm apart, and very large bulbs around 30 cm apart.

How to plant alliums?

Start by selecting healthy, intact bulbs. A few traces of mould are harmless; however, if the roots appear to be in poor condition, it’s better to discard the bulb.

In the ground:

• Clear the soil of weeds and stones.
• Loosen the soil to a depth of 20 to 30 cm using a spade or garden fork.
• Add organic matter, such as well-rotted manure, dried blood or crushed horn, to enrich the soil. The richer the soil, the larger the Allium will grow and the more floriferous it will be in subsequent years.
• Dig holes using a trowel or bulb planter, to a depth equal to three times the height of the bulb (e.g., a 5 cm tall bulb should be planted 15 cm deep).
• If the soil is heavy or clayey, improve drainage by placing a layer of sand or gravel at the bottom of the planting holes. You can also mix in some light potting compost with the soil.
• Plant the bulbs with the pointed end facing upwards, ensuring they do not touch each other.
• Respect the spacing between bulbs: 5 to 10 cm for small bulbs, 15 to 20 cm for medium-sized ones, and up to 30 cm for large bulbs.
• Cover the bulbs with a layer of soil equivalent to twice their height.

Whether in the ground or in pots, Alliums demand perfect drainage

In pots:

Allium bulbs can easily be grown in pots to enjoy their blooms on terraces or balconies. As with planting in the ground, drainage must be impeccable.

• Choose a deep pot with drainage holes to prevent waterlogging.
• Spread a layer of clay pebbles at the bottom.
• Add potting mix to the pot, ideally a blend of half garden soil, a quarter potting compost, and a quarter gravel or pumice.
• Plant the bulbs with the pointed end facing upwards, spacing them slightly and covering them with two to three times their height in soil.
• Water lightly after planting.

Mass planting

• Excavate an area of the flowerbed or lawn to a depth of 10 cm using a spade or garden fork.
• Arrange the bulbs according to their size, spaced 5 to 30 cm apart.
• Cover the bulbs with soil or the cut turf.

If planting in a lawn, cut out sections of turf, place the bulbs, and then reposition the turf after planting.

Don’t hesitate to plant Alliums en masse: guaranteed impact! 

How to care for them?

The tallest species, such as Allium giganteum, may require staking to keep their flower stems upright, especially in windy areas.

Watering alliums should be moderate. During the growing season, water only if the soil is very dry, up to twice a week during prolonged dry spells. In summer, when the bulbs enter dormancy, it is essential to keep the soil dry to avoid any risk of rot.

To encourage beautiful flowering, we recommend applying some fertiliser in spring, when the flower stalks begin to emerge. Use a specific fertiliser for flowering bulbs or enrich the soil with well-rotted compost or another organic amendment. This not only promotes the current flowering but also ensures the healthy development of the bulbs for future years.

After flowering, the faded flower stalks can be cut using secateurs if you wish to preserve the bulbs’ reserves or prevent self-seeding. However, if you appreciate the decorative aspect of the dried flower heads, you can leave them in place to extend their visual interest in the garden.

The foliage should only be cut once it has completely yellowed and dried. This allows the bulbs to replenish their energy reserves for the next flowering. Once the foliage has withered, it can be safely removed without harming the plant.