When to Plant Allium Bulbs for Beautiful Blooms in Spring, According to Experts

Allium bulbs blossom from the spring into the early fall, adding charm, texture, and color to the garden. They produce globe-shaped flowers in a range of pink, purple, and blue hues. However, these bulbs need to be placed in the ground at the right time in order to produce vibrant blooms. Here, we spoke to experts about when to plant allium bulbs, as well as how to properly care for them.

Varieties

Rhonda Kaiser, founder of Southern Home and Farm and author of The Vintage Farmhouse Garden, recommends Allium giganteum (‘Globemaster', ‘Gladiator’) because they have big purple globes on tall stems that add spark and texture to the garden—they're also great cut flowers.

Peggy Anne Montgomery, horticulturist with FlowerBulbs.com, suggests growing a combination of varieties. "By mixing different [ones], gardeners can stagger bloom times and keep the garden full of color from spring to fall, while also providing continuous food for pollinators," she says.

When to Plant

Allium bulbs should be planted in the fall so they can bloom in late spring.

"The best planting time for alliums is when soil temperatures are consistently 50 to 55 degrees Fahrenheit at bulb depth—cold enough to prevent sprouting, but warm enough to promote rooting," says Kaiser.

Place them in the ground before the first frost. "If planting late in a mild climate, pre-chilling bulbs in the refrigerator for 4 to 6 weeks can help mimic the cold period they need," says Laura Root, the senior merchant for live plants and hard goods at Jackson & Perkins.

It's important to pay attention to the soil temperature when planting. Bulbs planted in warm soil may have their dormancy period interrupted, which can lead to weak or failed blooms.

How to Plant

When planting bulbs, you need to consider how deep you place them in the soil and how you want them to look when they bloom.

"A good rule of thumb is to plant the bulb about two to three times as deep as it is tall, and space them roughly 6 to 8 inches apart, depending on the variety," says Linda Vater, plant expert at the Southern Living Plant Collection.

Bulbs need ample space to grow without overcrowding, so consider their size when determining how many to plant together. "Groupings of 12 to 25 small bulbs or three to six large bulbs create the most attractive displays," says Montgomery.

Allium bulbs combine well with herbs, adding more texture to the garden. "In a mixed border, I like to tuck them in among spring-blooming shrubs, as well as catmint, salvia, and chartreuse-colored foliage; areas where their strong vertical forms can really pop against softer textures," says Vater.

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Care Instructions

Allium bulbs are easy to grow as long as you provide them with adequate sunlight and water, as well as the proper soil.

"Once established, alliums require minimal care, and are naturally resistant to critter damage, pests, and diseases, which is one of the biggest issues with bulbs," says Montgomery.

Water

Allium bulbs need plenty of water when they're first planted and do best with moist soil. "Water well after planting, then keep the soil lightly moist until dormancy, and mulch to prevent heaving," says Vater. Heaving is when bulbs push up to the soil surface, which can be caused by temperature fluctuations, planting depth, and even the variety. 

When bulbs go through their dormancy period, they shouldn't be watered. "As soon as the soil freezes, stop watering, since bulbs are in their resting period and should not have too much water—or else they will rot," says Kaiser.

Sunlight

Plant allium bulbs in an area that receives ample sunlight. "In a garden bed, place them where they’ll receive at least 6 hours of direct sun a day," says Root.

Soil

These bulbs prefer well-draining soil. Plant them in beds or borders with good drainage or areas amended with sand or compost, says Root. Avoid planting them in clay soil, she adds.