How To Grow Allium or Ornamental Onion

Allium or ornamental onions are fantastic spring blooming bulbs that more and more savvy gardeners are tucking into their gardens. What's not to like about these cheerful bloomers? They are bone hardy if grown in well drained soil (sorry you clay garden folks – this is not your plant) and given a shovel of compost in the spring. They bloom regularly and if you control the early slugs, you are not likely to see any problems with this plant. And you have over 500 varieties to choose from – what could be better?


Because there are several different sizes of bulbs here, remember the general guideline to plant a bulb as deep as twice its length. So if the giant allium bulb is three inches high, then the bottom of the bulb goes six to nine inches deep.

My Favourite

My all time favourite of all ornamental onions is the Star of Persia or Allium christophii. Now, sometimes this one is sold under the name of A. albopilosum but it's the same plant. It is called the Star of Persia because of the fantastic seed pod that looks like a multi-pointed star.

Allium giganteum

Allium christophii

The flower is a metallic purple and beautiful and if you plant the bulb out in the full sun about four to six inches deep, this star will flower for years in your garden. Plant them four to six inches apart – and yes, you'll want more than one so just give in and order at least three to grow in a clump.They'll be about twenty four inches tall so do plant them where they will be easily seen.

Allium giganteum

Allium giganteum

Allium 'His Excellency'

Another truly spectacular show-stopper ornamental onion is Allium giganteum.(pictured)

This is truly a huge flowering bulb reaching forty eight inches tall on the stalk and producing a massive six inch blossom.

This one is quite hardy, is never bothered by pests (unless these pests are human or slugs) and easily grown.

Plant the bulbs four to six inches deep in a very sunny spot.

You want full sun with this one so the stems will stay stiff and upright.

Shade gardens will produce weak stems that flop over and there are few sights sadder than a flopped over allium when the flower is too heavy for the stem.

If you have to plant more than one of these ornamental onions, plant them at least eight inches apart. The plant breeders are using A. giganteum to give extra height and flower size to other hybrid bulbs. The best known of these is the cross between Allium giganteum and Allium stipitatum (native to Afghanistan) that is sold as 'Globemaster'. 'Globemaster' has a ten inch, silvery-violet blossom and will be a hit in any garden.

Smaller Variety

Allium moly is a smaller species that is well worth growing. A. moly is bright yellow and about ten inches tall. It begins blooming at the end of May to early June in local gardens and if planted in the full sun and 3 inches deep, it will live happily in your garden for years.

Allium moly

Allium moly 'Jeaninne'

In fact, if happy it will not only live where you plant it, it will live just about anywhere you don't want to weed it out of. (which accounts for why I haven't grown it before in my garden)

This is a bit of a spreader so do plan on weeding it out after a few years (I am). If you can find the cultivar 'Jeannine' purchase this because it has two flowering stems on each stalk rather than the single of the species. You'll get twice the blooms and twice the seeds.

This native of Southern Europe should be planted four inches apart. Plant about six in a small clump to get you started - after that move them around your garden or allow them to self sow to give a cheerful yellow show after the tulips are finishing.

One for hot and dry

Allium neapolitanum is a cheerful little bulb producing glistening star-shaped flowers held on 15 inch stems (give or take a few inches). The nodding buds open up to upward facing, glistening white flowers with yellow anthers. This is a bulb of the dry, open sunny spaces in Portugal and the Mediterranean. Do not put it in clay soils and do not grow it where it will get much summer moisture. Moist soils in the summer will simply kill it; it wants full, hot sun and baking, well-drained soils with no clay. While the flowers have a pleasant fragrance to them, as a native of southern climates, they can be a bit miffy in colder climates. Many gardeners do find however that they make excellent forcing bulbs.

Book cover spring bulbs

Most Interesting

The last, but not least, is Allium karataviense. This strapped-leaf shaped plant is well worth a place of honour in any rock garden or the front of a sunny perennial border. At eight inches tall, the four to six inch blossom is a bit unexpected but quite welcome in the early spring garden. There are a range of available colours - from pinks through violets - so grow them all. Plant these Alliums or ornamental onions three inches deep and three inches apart (you'll want lots of these) to give you a great show in the spring. If you've never grown them before, you'll be surprised by the almost lack of flower stem - the flower looks as if it were resting directly on the leaves.

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