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How to Grow: Alliums
full sun, part sun
Bloom Period and Seasonal Color
Spring to early summer in colors of white, pink, yellow, and purple
Mature Height x Spread
6 to 36 inches x 10 to 12 inches
Attract beneficials, drought tolerant, deer resistant
Alliums are a broad group of plants in the onion family. While we’re all familiar with good common food crops, such as onions, leeks, and garlic, there are many alliums that are grown just for their ornamental characteristics. The ornamental alliums are a diverse group. Some are only 6 inches tall producing dainty flowers, while others can stretch to 3 to 4 feet tall with 8-inch diameter flowers that are packed in a dense head. Most of these bulbs bloom early in the season providing a dramatic accent to spring flowering plants. I love seeing tall alliums popping up among my perennial flowers in spring. Combine their tough nature with deer and animal resistance and you get a reliable bulb that will bloom for years.
Where, When and How to Plant
Alliums are hardy in our region depending on the type. Select varieties hardy to your zone. Plant alliums in fall when you would tulips, daffodils and other spring flowering bulbs. Plant in a full sun location on well-drained, fertile soil. Alliums will grow in part shade, but may not flower as well. Plant bulbs 2 to 3 times their diameter deep. For example, a 2-inch diameter bulb should be planted 4 to 6 inches deep. Space the bulbs 3 to 8 inches apart, further apart for larger bulbs.
Alliums grow best in a fertile soil, so amend the soil with compost when planting and spread a light layer over the planting area each spring. Keep the bulbs well weeded and watered. Once established they’re drought tolerant. Alliums that a marginally hardy in our area should be mulched in fall with bark mulch to protect them for winters’ cold.
Regional Advice and Care
Stake tall varieties of alliums to prevent the flower stalks from flopping over. Dead head spent flowers in summer after the blooms have passed or let them form seeds and self sow in the garden. Self sown allium seedlings will need a few years of growing to get to the flowering stage and can become weedy if you don’t thin out the seedlings in summer. Let the foliage naturally yellow and dieback in summer before cutting it to the ground.
Companion Planting and Design
Alliums grow best tucked in a perennial flower border to “pop up” around other spring blooming flowers, such as peonies, iris, catmint, and geranium. You can also plant the large flowering varieties en mass for a dramatic effect or short varieties in a rock garden to complement other low growers such as columbine and sedum.
‘Purple Sensation’ is a large-flowered variety that grows 2 to 3 feet tall producing 4-inch diameter purple blooms. ‘Globemaster’ and ‘Gladiator’ alliums grow even taller (4 feet) with even bigger diameter (8 inches) with purple flowers. ‘Mt. Everest’ is a white flowered version. Drumstick alliums only grow 1 to 2 feet tall and produce 2-inch diameter reddish-purple blooms. Allium moly grows 8 inches tall with yellow flowers in loose clusters.
Excerpted from my book, New England Getting Started Garden Guide.