Posted by Aaron Barton on Mar 4th 2023

Allium (Ornamental Onion)

Tidy, colorful, and uniquely fragrant, Allium (AL-ee-um) species, or ornamental onion, are stunning mid-season bloomers that shine in low sunny borders or edging, cottage gardens, and other sunny garden spaces. Especially impactful when planted in large groupings, ornamental onion’s appeal expands beyond perennial beds, serving as a wonderful addition to annual container arrangements and great as either fresh or dried cut flowers as well.

Belonging to the Amaryllis family, Amaryllidaceae, Allium is a massive genus of well over 500 species native across temperate regions of the northern hemisphere, distinguished by their true bulbs and onion or garlic aroma and flavor, imparted by the production of cysteine sulfoxide compounds, the potency of which is directly related to the soil’s sulfate content, helping to also keep deer and rabbit feeding at bay.

Despite their name, ornamental onion should only be admired for their phenomenal blooming displays, blooming from mid-summer to late summer, often into fall. Not to be confused with the fall-planted, spring-blooming large Allium bulbs, ornamental onion produce multiple blooms high above the foliage on leafless scapes or stems arising directly from the bulb. Blooms are spherical two- to three-inch firework-like umbels of star-shaped pink or purple flowers which bloom progressively from the outside inward. After blooming, spent stalks may be removed or left to develop attractive black seed pods for winter interest, or cut for use in dried arrangements (just be sure to keep them away from pets!).

Forming lush clusters as their bulbs slowly form offsets, Allium produce up to 12 flat, succulent green upward-facing leaves per bulb, maturing to an attractive mound 18-24” tall and wide. One of the most popular cultivars available, the heavy-blooming ‘Millennium’ glows with midseason rosy purple blooms, blooming slightly later than ‘Windy City,’ another excellent cultivar offering a slightly more compact plant of only about 16” tall and wide with early lavender blooms atop rigid, dark green scapes.

Allium prefer full sun conditions in moist, well-drained soil, tolerant of drought and high salt conditions, but will not tolerate poorly drained soil or consistently wet conditions.

Happy planting!