purple allium flowers

How To Plant Allium Bulbs: A Complete Guide To Growing Ornamental Onions

Ornamental alliums are a delight in the garden, and one of my favorites of the spring-flowering bulbs. Allium bulbs are easy to grow if you follow a few simple steps. In this guide, I’m going to share with you everything you need to know to grow beautiful allium flowers, year after year.

How to plant allium bulbs

Although alliums flower from late spring to early summer, the bulbs are planted in the fall. Allium bulbs need a period of cold to flower, and planting in the fall gives them a full winter to achieve this cold dormancy. After this period of dormancy ends, alliums will provide you with weeks of stunning flowers.

Alliums are easy to grow, deer resistant, and a favorite of butterflies and hummingbirds. Alliums need full sun to bloom and are a garden perennial. Think long term when planting your alliums, because they will return year after year with their cheerful globes. Taller varieties need shelter from the wind, and shorter varieties belong in the front of beds, where they won’t be hidden by taller plants.

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Alliums are a great addition to both pollinator gardens and cut flower gardens. The flowers will last for weeks in a vase and provide interest in the garden long after the flowers have gone to seed. Some gardeners even spray paint their alliums after the flowers fade, to provide additional pops of color to their late summer garden. 

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What are allium flowers?

Alliums, also known as ornamental onions, are sphere shape pops of color in the summer garden. Alliums are long lasting, easy to grow, and make excellent cut flowers.

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Allium flowers come in many beautiful varieties, and several different heights and sizes. Some varieties of allium tower over the garden, while shorter alliums add a splash of interest to the front of flower beds.

Giant alliums, such as Gladiator or Purple Sensation, have tall stems reaching up to 60” tall. The flower heads can reach 5” inches across. These alliums are eye-catching even from great distances. Giant allium should be planted in a sheltered spot, to avoid damage during heavy winds.

Smaller varieties, such as Drumstick allium or Blue Allium add texture and interest to flower beds. These typically grow 2-3 feet in height, with flowers growing in a 1”-3” diameter. Planting several types of alliums together, in different colors, heights, and size, make a stunning addition to the spring garden.

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When to plant allium bulbs

Alliums can be planted in both spring and fall, although fall is the preferred time. Alliums do best when planted in their dormant state. For planting alliums in the spring or fall, plant according to the directions below.

When to plant allium bulbs in pots

Planting allium bulbs in pots is the same as planting in the ground. Fall, during their dormant state, is preferred, but spring is a second best option.

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How to plant allium bulbs:

  1. Choose the right location. Alliums prefer well-drained soil, and need full sun to bloom. For best results, choose a planting location with good drainage, and avoid heavy soil, lots of clay or too much shade.
  2. Dig a hole. Alliums are best grown in clumps or drifts, as they are more impactful to the landscape planted in groups. To plant in groups, lay your alliums on the surface of the soil in the pattern you’d like the flowers displayed. Each bulb should be 3x it’s width apart from the other bulbs. Mark this area with a shovel. Set the bulbs aside and dig a narrow trench inside your marked area that is 2-3 times as deep as the size of the bulb. Note: Alliums should be planted at a depth that is 2-3 times as deep as they are wide.  For bulbs that are 1 inch wide, plant them 2-3 inches deep. Bulbs that are 2 inches wide need to be planted at a depth of 4-6 inches, and so on.
  3. Add bone meal to planting hole. Bonemeal is an excellent organic fertilizer to boost the growth of spring flowering bulbs, such as alliums, daffodils, and tulips. Add 1tsp to the planting hole of each bulb or sprinkle 1 tsp per bulb in the planting area before placing the flower bulbs in your trench. You can find bonemeal here, or at your local garden center
  4. Place alliums in planting hole. Alliums are planted with the flat side down and the pointy end facing up. Cover them with soil, and lightly pat the soil in place. Water them well after planting. Next spring, you will be rewarded with their eye-catching blooms!
purple allium flowers
Alliums are striking in the garden and add unique interest to the landscape

How To Grow Allium Flowers

After planting, alliums can pretty much take care of themselves. Occasionally they may need staking, especially if you live in an area with high winds.

Keep them evenly moist during the growing season. Be sure to avoid soggy soil, as this can cause the bulbs to rot.

Removing the flower clusters is fine in either the dry or fresh state, but keep the foliage intact. The foliage needs to turn and yellow and die back on its own, as it’s storing nutrients for next year’s blooms.

Allium flowers can be left in place all winter long. They offer winter interest during the cold season, when most of the garden has died back or is covered in snow.

How To Grow Alliums FAQ

Can I grow alliums in containers?

Alliums do well in pots and look stunning in containers. When planting in pots, use an all-purpose potting mix and a well-draining container. Allium bulbs can be planted a little closer together in containers than they would be in the ground.

How long do alliums bloom?

Alliums bloom from late spring to early summer, with a long bloom time for each flower. Allium flowers can last anywhere from 2-4 weeks, making them a great choice for early summer blooms.

Are alliums good cut flowers?

Alliums make great cut flowers. They stay fresh for weeks and are a unique addition to a cut flower display. They’re sturdy stems make them easy to arrange in a vase. Cut them when their flower buds are ¼ to ½ open. This will give you the longest display of flowers in the vase, as they’ll continue opening after cutting, as the older buds fade.

How long do alliums last in a vase?

Fresh alliums can last 2 weeks in a vase, with proper care. The trick is to cut them before all the flower heads have opened, so new buds are opening as the old buds fade. Each bud lasts for 4-5 days, with the entire flower head blooming for up to 2 weeks. Alliums also make excellent dried flowers. 

How do you keep alliums fresh?

To keep alliums fresh and prolong their vase life, cut the stems on an angle and place into fresh water immediately. Every 2-3 days, replace the vase water with fresh water. After a full week, cut a centimeter off the bottom of each stem, on an angle, and place back into fresh water. Alliums should last up to 2 weeks in vase if properly cared for.

Do allium bulbs multiply in the ground?

Alliums are clump-forming perennials and will multiply on their own. Large bulbs begin multiplying 1-2 years after planting, while smaller bulbs multiply after 2-3 years. Alliums also form seed heads, which can be collected and replanted, although the seeds won’t be true to the parent plant.

How deep should you plant allium bubs?

Allium bulbs should be planted at a depth twice to three times as deep as the length of the bulb. For bulbs that are 1 inch wide, plant them 2-3 inches deep. Bulbs that are 2 inches wide need to be planted at a depth of 4-6 inches, and so on.

Do alliums bloom the first year?

Large allium bulbs will bloom the first year after planting. Smaller allium bulbs, and alliums grown from seed, may take 2 years to begin blooming.

How many allium flowers per bulb?

Each allium bulb produces one flower head atop one sturdy stem. Each flower head is made up of many individual flowers in the shape of a globe.  

Are alliums deer resistant?

Being a part of the onion family, alliums are very deer resistant. Deer have sensitive noses and tend to avoid plant they find “stinky.” This includes alliums and makes them an excellent choice for gardens with deer pressure.

Do alliums attract pollinators?

Alliums are a great way to attract bees, butterflies, and hummingbirds, who are drawn to the eye-catching allium blooms. Planting alliums will attract pollinators to your yard, and their beautiful blooms are an excellent addition to a pollinator garden.

Do alliums come back every year?

Alliums are perennials, which means they return to the garden year after year. Alliums will even form new allium bulbs after several years. These bulbs can be dug up and planted elsewhere in the garden, where they will return the following year.

Are alliums drought tolerant?

Alliums are tolerant of dry periods and prefer to be on the dry side to prevent bulb rot. Alliums grown in containers will require more watering than alliums planted in the ground. If planting in containers, choose a well-draining soil mix and water when the top 2 inches of the soil feels dry.

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How To Plant Allium Bulbs: A Complete Guide To Growing Ornamental Onions

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