Are Ornamental Alliums Annual, Biennial, or Perennial Plants?

Thinking of adding allium to your garden, but aren't too sure if they will come back each season? In this article, certified master gardener Laura Elsner takes a deeper look at the life cycle of ornamental alliums so you'll know what to expect when you add them to your garden this season.

Written by Laura Elsner Last updated: October 2, 2023 | 3 min read

Contents

Are ornamental alliums perennial? Will they come back every year? When creating a garden or adding new plants to a garden, it is important to know the types of plants you are getting.

Planting a bed full of annuals but expecting them to come back year after year (aka perennial) will lead to frustration and disappointment. So where do ornamental alliums fall into this spectrum? Will you see them bloom year after year, or be disappointed next season?

Let’s examine each planting category further to determine if planting alliums is right for your garden.

The Short Answer

Alliums are considered herbaceous perennials. They grow in USDA hardiness zones 3-8. They will come back every year and can even multiply if they are planted in their ideal conditions.

The Long Answer

Multiple alliums are shown with small, white clusters of flowers attached to slender, upright, green stalks. a The leaves are long, narrow, tubular in shape and green in color. — Understanding the plant types is crucial when creating or adding new plants to a garden.

The Allium genus includes ornamental globe-shaped flowers and edible onions, garlic, and leeks. The lifecycle of each plant depends on the species, your climate, and how you prefer to grow the plant.

What are Annuals, Perennials, and Biennials?

Close-up of an Allium flower which are small, star-shaped, and lavender in color. The clusters of flowers are spherical in shape. The leaves are large and green in color. — Depending on their growth cycle, plants are classed as biennial, perennial, or annual.

Plants are generally categorized as being either annual, perennial, or biennial. This has to do with the growth cycle of the plant.

Annuals complete their growth cycle in a single season. This means the plant will grow, bloom, and seed itself every season. A classic example of this is a marigold. While you might have marigolds growing every year, they are new plants grown from the seeds of last year’s marigolds.

We also will sometimes refer to tender perennials as annuals. This means the plant would be perennial in a higher USDA hardiness zone. But it freezes and dies in colder zone gardens. For example, coleus are technically tender perennials often considered annuals in lower zones.

Biennials take two seasons to complete their growth cycles. They will establish and grow in the first season, then flower and set seed in the second season. An example of this is carrots.

Carrots are actually biennial. You can plant and harvest a carrot in a single season. But if you want carrot seeds, you have to keep the carrot in the ground, and it will bloom and set seed in the second season.

Other biennial plants include foxglove and hollyhock. Again, you may think these plants are perennials because you will always have hollyhock growing in an area. But they are actually new plants that are growing in a continuous two-year cycle.

Perennials are plants that establish roots and grow from those roots every season. Some perennials live a long time. Peonies, for instance, are proven to live for over one hundred years!

There are different types of perennials. Herbaceous perennials die back every season and regrow. This includes hostas and alliums. There are also evergreen perennials that will remain green year-round. This includes bergenia and the ground cover candytuft.

About Alliums

There are rows of various Alliums. The second row is higher and taller, with spherical, lavender blooms clinging to their long, green stalks, as opposed to the first row, which is still young and has little flowers. The Alliums in the following row have white blooms, and the remaining rows have a combination of lavender and white blossoms. — Alliums typically refer to ornamental species with grass-like foliage and round, multicolored flower orbs.

Now let’s dig into alliums. Alliums are a large genus of plants. They include garlic, onions, and chives. However, here we are discussing the ornamental allium varieties grown for their flowers.

This includes Allium giganteum, A. hollandicum, and A. schubertii, to name a few. They have grass-like foliage on the bottom and round orbs of flowers that are comprised of many tiny flowers. They come in lots of different shapes, sizes, and colors.

Alliums are bulbs that are planted in the fall. They require a period of cold dormancy before they can grow. Purchase or acquire bulbs and plant them as deep as about three times the bulb’s diameter.

Water them in well and then forget about them. You can plant them in the ground or into containers. For container-grown alliums, make sure you are in zones 5 or higher for them to survive the winter.

The plants will emerge from the soil in early spring. They will sprout grass-like foliage at first, then a flower will rise from the center and bloom. Generally, you will get one bloom per allium bulb (this is variety dependent).

As the flower is in bloom, the bottom foliage will start to turn brown and fade. After the flower blooms, it will turn into a seed head. The stalk and bottom foliage will easily pull out of the ground when it is ready. It has finished for the season. Next year the allium will grow all over again.

Growing Allium

Three small, brown, spherical allium bulbs that resemble onions have a dry, papery outer layer that covers them to preserve the inner layer. Their bases are being planted on top of a dark soil surface. — Any well-draining soil will do; just don’t allow the bulbs to dry up or sit in overly wet conditions.

Alliums are a fairly easy plant to grow. As outlined above, they are a bulb that is planted in the fall.

Plant your allium bulbs in an area that receives full-part sun. If they aren’t getting enough sun, they will not bloom. Partial sun is the sweet spot. Too much full sun and the blooms will fade faster.

Alliums require a medium amount of water. Make sure to water the bulbs when you first plant them thoroughly. Then just your regular watering schedule for your perennial garden beds should suffice.

Don’t let them dry out. On the other hand, don’t let the bulbs sit in soggy conditions. The bulbs will rot. Loose, rich soil is best, but allium will do ok in sandy or clay soil. As long as the soil can drain, it should work well.

What Makes Alliums Perennial?

Multiple allium bulbs planted on the ground are shown. They small, white, and oblong in shape. At the top of the bulbs are fleshy, green shoots that will grow into a stem and eventually a flower. — These perennial plants store energy in bulbs, growing and dying back each year.

Alliums are perennials because they will grow and die back to the same bulb and continue this cycle year after year.

Make sure to allow your allium to keep its green foliage as long as possible, this is how the plant gains and stores enough energy to grow again the next spring.

What Zones Are Alliums Perennial In?

In the center of a field of plain green grass, a variety of plants bearing beautiful flowers and green leaves have been planted. Alliums are noticeable for their large, spherical lavender blossoms. — These plants require a cold dormancy period to grow, thriving only in zones 3-9.

Alliums are perennials in zones 3-9. They do not thrive in zones higher than that because they require a period of cold dormancy to grow.

While there are a few varieties that don’t mind a warmer winter, they aren’t as vigorous without it!

How Many Years Will Alliums Last?

A close-up of many round, spherical, or domed Allium flowers that are composed of several tiny individual flowers grouped tightly together in a dense head. On long, slender, fleshy stalks, lavender flowers are held high. — The bulbs develop underground and can generate new growth in about five years.

The lifespan of this plant is variety-dependent. A good estimate is around five years. But this doesn’t mean you’ll have no allium in 5 years. The bulbs multiply underground. So you’ll have new bulbs growing if they are in their ideal conditions.

It could be environmental factors if your allium disappeared in only a season or two. Too much water will rot your bulbs. They cannot handle sitting in standing water.

Another reason could be the bulbs have divided, and they are getting too crowded. In the fall, lift the bulbs out with a trowel, shovel, or garden fork. Take all the small bulbs surrounding the main bulb out and transplant them in different areas in your garden. Or give them away to friends and neighbors.

Final Thoughts

Alliums are wonderful herbaceous perennials to add to your garden. They grow and bloom in the spring. Allium will come back year after year. They require minimal effort and will reward you with big beautiful blooms.

Are Ornamental Alliums Annual, Biennial, or Perennial Plants?

The Short Answer

The Long Answer