Ornamental Onions Allium

Allium, commonly referred to as ornamental onions, are bulbous herbs that are characterized by their onion or garlic odor originating from their long, basal foliage. The genus contains hundreds of species and include the ornamental ones plus the garlic and onions we grow for food. Many are native to the northern hemisphere where they can be found growing in dry, mountainous regions. Although they are cultivated within the landscape, in nature ornamental onions can be found growing in forests and are present as a weed in disturbed areas. The genus contains approximately 700 species; most of which bloom between late spring and early summer. 

The easiest method of propagation for ornamental onions is division as they are easily grown from bulb offsets. These should be divided and planted in spring for the best results. Sowing from seed is also an option but some seeds may take years to germinate. After flowering, the foliage may look unwell so the leaves should be cut back to revive the plant’s interest. To protect plants over winter months, dig and store any non-hardy species. 

Ornamental onions are great for border gardens, rock gardens, edible gardens, or as a mass planting. They should be planted in full sun in rich, sandy loam well-drained soil at a depth of 5-8 inches and 6-12 inches apart. They bloom in late spring to early summer.

Pests, Insects, and Other Plant Problems: Overly damp conditions leave ornamental onions prone to fungal issues, including bulb rot, white rot, rust, and mildew.

VIDEO created by Andy Pulte for “Landscape Plant Identification, Taxonomy and Morphology” a plant identification course offered by the Department of Plant Sciences, University of Tennessee.