Ornamental Onions

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Nearly all of the estimated 500 to 600 species in the genus Allium are native to the Northern Hemisphere, yet only a dozen or so of the ornamental spe­cies are widely available. Many are characterized by round, puff-ball heads of flowers, and they range in size from tiny plants suitable for the rock garden to strapping giants.

One onion rises above them all—A. giganteum. It’s a mainstay of Dutch bulb catalogs, which routinely display the obligatory photo of a child holding onto the stem of this 4- to 6-foot purple lollipop of a flower. (This picture is so common that I sometimes wonder if they actually ship a blond child with large orders.)

I’ve been immune to the dubious charms of A. giganteum. Its image almost put me off ornamental onions altogether. “I only like the ones I can eat, and they belong in the vegetable garden,” I used to tell myself. I’ve learned, little by little, to eat my words. Ornamental onions vary considerably in color, size, and form. Undemanding in their cultural requirements, they make rewarding additions to beds and bord­ers. I begrudgingly admitted a few to my perennial plantings, and they gradually won me over with their good looks and usually gracious manners.

As my interest in ornamental onions grew, I discovered how easy they are to grow. No back-breaking labor is required to get them into the ground, as most are planted just a few inches deep. They can take clay or sandy soil, although most thrive best in well-drained sandy loam. All demonstrate at least moderate drought resistance, and most will rot if overwatered. Alliums are quite hardy throughout the country and are best planted in autumn. Most grow well in pots if suitable quarters such as a cold frame can be provided in the winter in the northern states. They are rarely bothered by diseases or pests. I’m hard pressed to remember so much as an aphid on any allium in my garden. Some, however, attract butterflies and bees. Most alliums are long-lived and rarely if ever need dividing. Most will self-sow in moderation; only a few are intent on world domination.

The foliage is insignificant or even negligible on most ornamental alliums; there’s no giant death scene such as that put on by prima donna bulbs such as tulips and daffodils. The leaves of many species have all but disappeared by the time the flowers bloom, so a companion plant is an aesthetic necessity to cloak the bases of the naked stems. It’s possible to exploit this trait to advantage. An ideal way to showcase smaller alliums is to plant them beneath front-of-the-border, shallow-rooted pe­ren­nials such as creeping veronicas or phlox or in the spaces between larger clump-forming perennials such as cranesbill, catmint, or lavender. The tall, thin-stemmed species can be given a spot among lower-growing companions for an airy and often whimsical ­effect.

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