University of Vermont
Department of Plant and Soil Science

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PERENNIAL PLANT FEATURE: ALLIUMS

Leonard Perry, Horticulture Professor
University of Vermont
   
Alliums (said as al-e-UMS) are often known as ornamental or flowering onions, yet this name doesn’t really do justice to this easy-to-grow, hardy, perennial grown from bulbs.  This was the first year that the National Garden Bureau named a Bulb of the Year, and the winner was the ornamental Alliums.
   
Ornamental alliums, as contrasted to their vegetable kin (onions, leeks, garlic and chives to name a few), are grown for their usually globe-shaped flowers, made up of many individual star-shaped florets.  These are atop stems that arise from a basal clump of leaves, ranging from wide to narrow depending on the species.  Leaves of many go dormant later in summer when perennials take over the show.
   
Allium stems can range from one to five feet high, again depending on the species or cultivar (cultivated variety).  Most are grown from bulbs, ordered from spring until fall, and planted in the fall for bloom the following season.  The widest selection is usually found in catalogs and online.  Depending on species, bloom time can range from early summer to fall.
   
The showiest and perhaps most popular, and most often seen alliums, are those with large flowers, 5 to 10 inches wide on stems 2 to 4 feet high.  The aster-violet ‘Globemaster’ and lavender-blue ‘Gladiator’ bloom in late spring to early summer, after the daffodils and tulips.  ‘Stratos’ is similar to ‘Gladiator’, only with slightly larger and paler flowers.  These all combine well with bearded and Siberian iris.  When planting, space bulbs 8 to 10 inches apart, and plant 6 to 8 inches deep with the pointed side up.  ‘Ambassador’ is similar, blooming just after these though, and with rich purple flowers.

The first to bloom though, before these larger ones, is the most widely planted allium ‘Purple Sensation’.  Its raspberry-purple softball-sized flower heads are on stems 2 feet or so tall.  Blooming about the same time as ‘Purple Sensation’, with similar size flowers and nice combined with it, is the white ‘Mount Everest’.  Consider combining these with columbines.
   
Also blooming about the same time in early spring is the golden garlic or lily leek (Allium moly) with golden, starry flowers in clusters atop one foot stems.  Or combine it with the cultivar ‘Powder Puff’, having large lavender-purple globes on stems about one and one-half foot high.
   
One of my favorite alliums, blooming in late spring, is the tumbleweed or Schubert flowering onion (Allium schubertii).  Flowers are fist-sized, rose-purple, and with a unique shape—a spidery, wide oval with individual floret stalks of unequal lengths—similar to an exploding fireworks. This heirloom dating to 1843 gets one to two feet high. Plant one bulb per square foot.  Similar is ‘Spider’, only blooming mid-summer with deeper violet flowers, and the less hardy (USDA zone 5 minimum) Stars of Persia.
   
Much smaller flowers, only one inch across and a unique clear blue, are held one foot or more high on the heirloom blue globe onion (Allium caeruleum).  Space these about 3 inches apart when planting.  They contrast nicely in many areas with early peonies. The nodding onion (Allium cernuum) also blooms early summer, its unique dainty pink flowers nodding or hanging down. It is one of about 100 species of alliums native to North America.
  
Blooming later—late June in many areas—is the drumstick allium (Allium sphaerocephalon).  The wine-colored egg-shaped flower heads, resembling drum sticks, are produced on two foot high wiry stems.  This heirloom, dating back to 1594, contrasts nicely with many lilies and early daylilies.
   
Also appearing in late June, and often lasting until August, is the new cultivar ‘Summer Drummer’.  Its purple and white globe flowers, the size of grapefruits, are held on stems 4 feet or more high.  Interplant this with daylilies, ornamental grasses, or perennial geraniums.  Slightly lower in mid-summer, with pink flowers, is ‘Pink Jewel’. Even lower—about one foot high—is the yellow allium (Allium flavum). You may find several other good mid-summer blooming alliums such as the purple ‘Millenium’ or the light pink ‘Sugar Melt’.  Use caution with both the yellow and Moly onions, which can self-seed prolifically and are even invasive in some areas. 
   
For an unusual effect, ‘Hair’ allium has tentacle-like green flowers at all angles from a rosy base.  Circle onion is so called from its twisted blue-green leaves giving a corkscrew effect, from which the deep pink flowers arise. 

For late summer, garlic chives (Allium tuberosum) is at home both in the herb garden, and as an ornamental for its pure white flowers under two feet high.  ‘Ozawa’ Japanese onion begins blooming in September when the bees are looking for blooms.  The orchid pink flowers are held under two feet high.
   
These are a few of the more popular ornamental alliums, depicting a range of heights, colors, and bloom times.  Most are hardy to USDA zone 4 (minus 20 to 30 Fahrenheit winter minimum temperature), and are drought tolerant.  They’ll grow in most soils, as long as soils are well-drained.  They prefer, and bloom best, in full sun.  Fertilize on top of the soil after planting and each year as shoots emerge.  Use an organic fertilizer, or one formulated just for bulbs. 

Alliums have few, if any, problems bothering them, including deer and rodents who don’t like the taste of onions. Consider alliums, too, not just for gardens but for cut and dried flowers.


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