Types of allium: the most beautiful ornamental onions

The giant onion and round-headed leek are probably the best-known and most popular species of allium in our gardens. This beautiful bulbous plant has many more varieties to offer, however.

Ornamental onions belong to the allium family and decorate the garden in very different ways. Whether in the form of small, oval flowerheads as in the round-headed leek (Allium sphaerocephalon) or in the form of large, purposeful flower spheres as in the giant onion (Allium giganteum). We present an overview of the most beautiful Allium species and varieties.

Ornamental onion varieties and species: How many are there?

The genus Allium includes about 800 species. Among them are many vegetables, spices, and even about 40 species that serve us mainly as ornamental plants. Allium species occur worldwide, but the majority occur in the Northern Hemisphere. Doubly useful species include wild garlic (Allium ursinum) and chives (Allium schoenoprasum), which, in addition to their delicious taste, bring with them an ornamental value not to be ignored.

The most beautiful allium varieties and species at a glance

From this fascinating variety of species and varieties, we have put together a nice selection for you.

Giant onion (Allium giganteum)

The special feature of the giant onion is its flower balls, which average up to 12 cm in size and bloom fantastically from June to July. Its leaves can grow as long as 45 cm. In full bloom, giant onion reaches a height of up to 150 cm and tolerates temperatures down to – 17 °C. This species likes to stand alone or in small groups of 3 to 5 plants in a well-drained to fresh soil. Giant onion is also one of the most important parent species for many tall-growing ornamental onion hybrids.

Star of Persia (Allium cristophii)

Star of Persia is one of the ornamental onion species with the largest flower spheres. These can reach a diameter of up to 25 cm and have purple, star-shaped individual flowers. This species blooms from mid-June and in this state reaches a height of between 20 and 40 cm. Plant the bulbs at a distance of 30 to 50 cm, i.e. about 5 to 10 plants per m². Star of Persia only tolerates temperatures down to – 11 °C.

Tip: Star of Persias are wonderful for dry bouquets because the petals hold up even when dried. In many species, these fall off, which is why there only the seed head can serve as an ornament.

Schubert’s allium (Allium schubertii)

Schubert’s allium grows comparatively low and is most notable for its bizarre, loose flower sphere. It grows to a height of 40 to 50 cm and has a flowerhead diameter of 35 cm. At the same time, this species prefers to stand solitary. Therefore, plant a maximum of 6 plants per m². Theoretically, this species should easily survive temperatures down to – 17 °C. Still, treat Schubert’s allium to winter protection of brushwood or foliage to get them safely through the frosty temperatures.

Bulgarian honey garlic (Nectaroscordum siculum subsp. bulgaricum)

Strictly speaking, this species no longer belongs to the Allium genus (formerly Allium siculum) – but as an allium, this beautiful variety should not be missing from our collection. Bulgarian honey garlic stands out from other Allium species with its funnel-shaped, pale purple flowers. It reaches a height of 80 to 100 cm and should be planted with a planting distance of 30 cm, i.e. a maximum of 11 plants per m². It shows off its special flowers from May and tolerates temperatures down to – 17 °C. Bulgarian honey garlic prefers a well-drained and permeable site, as well as a soil rich in lime.

Round-headed leek (Allium sphaerocephalon)

Round-headed leek is one of the most popular ornamental species. It reaches a height of 70 to 90 cm and bears dark purple flower balls from the end of July, which reach a diameter of 4 cm. Due to its manageable size, 16 plants per m² can be planted without any problems. This species can overwinter at temperatures as low as – 28 °C and, unlike most species, is evergreen. Round-headed leek is wonderful for dry meadows, i.e. nutrient-poor but species-rich meadows. Nitrogen-rich fertilising should be absolutely refrained from, otherwise the plant will tend to buckle.

Note: Bulgarian honey garlic and round-headed leek are examples of Allium species that require calcareous soils. That is, they in no case tolerate too acidic soil – rather, the pH should be close to 7 or slightly higher. Garden lime can be used to neutralise natural soil acids and also benefits many soil organisms and soil structure. To determine if your garden soil is too acidic, soil pH tests can be used.

Yellow garlic (Allium moly)

Yellow garlics also take on a slightly different flower form and bloom a brilliant yellow, even in sunny locations. Yellow garlic grows up 20 to 30 cm in full bloom. This species is very frost resistant and tolerates temperatures down to – 40 °C. It germinates abundantly, which leads to numerous stocks. It is therefore very suitable as a wild perennial and may be planted densely with 200 to 400 plants per m². The variety Allium moly ‘Jeannine’ is very special among the Allium plants due to its two flowerheads per bulb.

Very-dark purple onion (Allium atropurpureum)

Let us stick with dark purple flowers and get to purple allium. Its flowers form a flower umbrella rather than a sphere. Flowering begins in June, with a growth height of 80 cm. Ideally, plant a maximum of 16 plants per m² at a distance of 25 cm. Temperatures as low as – 17 °C are no problem. Purple allium is excellent for drying and keeps well as a cut flower in water.

Blue-flowered onion (Allium caeruleum)

As its name suggests, the blue-flowered garlic bears blue flower balls. They bloom in June and reach a diameter of 4 cm. Growth height is 40 – 50 cm. Despite the fact that blue-flowered garlic is very frost-hardy and survives temperatures down to – 40 °C, it loves especially warm and sunny places. Therefore, make sure that there is no shading competition nearby. Waterlogging should be avoided at all costs. With a plant spacing of 20 cm, 25 plants per m² are able to grow well.

Black garlic (Allium nigrum)

Here the name is misleading. Except for its seeds, there is nothing black on black garlic. It bears beautiful white, semicircular flowerheads that reach 5 inches in diameter and keep well as cut flowers. This species in no case tolerates waterlogging and heavy soils. Black garlic likes to stand solitary, but with a maximum of 5 other neighbours per m². With a comparatively higher fertilisation requirement, it blooms from May to June and reaches a height of 60 cm. For example, our organic Plantura Flower Food is very suitable for allium plants.

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The NPK ratio of 4-2-7 is tailor-made for ornamental onions. With its long-term effect, two fertiliser applications per year are enough to bring the plant well through the season. Spring and late summer are ideal – this is when demand is highest.

Kara Tau garlic (Allium karataviense)

Last but not least, we would like to introduce you to the noble Kara Tau garlic. Its pale, purple flower balls grow up to 10 cm in diameter and appear as early as April. Its greenish-greyish foliage harmonises with its pale flowers. In flower, this species reaches a height of 30 cm and survives temperatures of – 17 °C. Up to 11 plants per square metre can be planted. Soils that are too rich in humus are not tolerated by this species and lead to bulb rot in winter. Ideal locations for are rather dry, for example, rock gardens.

Kara Tau garlic varieties:

• Allium karataviense ‘Red Giant Star’: It bears pale, wine-red flower globes with a growth height of up to 25 cm. The flowering period extends from May to June. Frost-sensitive ornamental onion tolerates maximum temperatures down to – 1 °C, so it is often cultivated in tubs. It likes to stand alone and is one of the more costly Allium species.
• Allium karataviense ‘Ivory Queen’: This variety with pure white flowers grows to a height of up to 30 cm. In this case, the diameter of the flower is from 15 to 20 cm. With a flowering period starting in May, ‘Ivory Queen’ tolerates temperatures as low as – 23 °C. 12 to 15 plants per m² provide enough space for healthy growth.

Allium hybrids

• ‘Ambassador’: Purple-pink flowers with a flowerhead diameter of 10 to 12 cm characterise this ornamental onion. When in bloom, it reaches a growth height of up to 130 cm and blooms from mid-June. ‘Ambassador’ likes to stand alone and tolerates temperatures down to – 17 °C. Ideally, plan for a maximum of 2 plants per m².

• ‘Mont Blanc’: It blooms from mid-May with white flowers and a flowerhead diameter of 8 cm. Its growth height when in bloom can range from 80 to 100 cm. ‘Mont Blanc’ is very nitrogen demanding compared to other ornamental onion species and tolerates temperatures as low as – 11 °C. Most tall-growing species like to stand alone or at most in small groups. As a guidance, consider 10 plants per m².

• ‘Gladiator’: This Allium hybrid reaches a growth height of 130 to 150 cm when in bloom. In mid-May, the purple-pink flowers appear with a flowerhead diameter of 10 to 12 cm. ‘Gladiator’ also likes to stand on its own – a maximum of 3 to 6 plants per m². This species tolerates temperatures down to – 11 °C.

• ‘Mount Everest’: These plants are true loners and should only be planted two per m². From the beginning of June, the white flowers appear with a flowerhead diameter of 8 to 10 cm, reaching a growth height of 100 to 120 cm. ‘Mount Everest’ survives temperatures as low as – 17 °C.

• ‘Purple Rain’: It blooms from the end of May in purple with a flowerhead diameter of 10 to 15 cm. During flowering it reaches a growth height of 80-120 cm. ‘Purple Rain’ can survive to – 17 °C and likes to stand in small groups – maximum 4 plants per m².

• ‘Globemaster’: This ornamental onion has a distinctly sturdy stem and shows its purple flowers from the beginning of May. At this time it can reach a growth height of up to 100 cm and a flowerhead diameter of 25 cm. Plant only 2 specimens per m² to ensure a distance of 60 cm. Temperatures as low as – 17 °C are no problem for ‘Globemaster’.

Are you planning to plant alliums? Learn about how to plant, when to plant, and how best to care for alliums in our dedicated article.