How to Plant, Grow and Care For Ornamental Allium
Thinking of adding Allium to your garden this season, but aren't sure where to start? Allium can act as a lovely ornamental, but also a wonderful companion plant. In this article, certified master gardener Laura Elsner walks through everything you need to know about Allium, including tips for maintenance and care.
Alliums are a large genus of plants that include familiar plants like garlic and chives. However, when gardeners speak of allium, we generally mean the ornamental varieties that are grown for its beautiful flowers. Allium is often sought after for its well-known, beautiful purple blooms.
Alliums are a fairly low-maintenance perennial bulb. They are planted in the garden during the fall and will produce beautiful flowers in the spring.
So, if you’ve decided that you’d like to grow allium this season but aren’t sure where to start, you’ve come to the right place. Keep reading to learn all about this popular perennial bulb and its care.
Allium Plant Overview
Plant Type Perennial
Native area Northern Hemisphere
Hardiness Zone 3-8
Exposure Part sun-sun
Plant Spacing Variety dependent
Planting Depth 3x as deep as bulb diameter
Height 5″-6′ (variety dependent)
Width 6″-2′ (variety dependent)
Watering requirements Moderate
Pests Allium leaf miner
Diseases Rot, Powdery Mildew
Soil Type Light, hummus
Attracts Bees, butterflies
Plant with Hosta, hydrangea, pansy, tulips
Allium is the Latin word for garlic. It is a bulb with a pungent, unmistakable garlic smell. Allium was essentially only used as food, a flavoring, and medicine throughout history.
It was used throughout the northern hemisphere by many ancient civilizations. It only became popular as an ornamental plant in the 19th century.
Alliums are members of the Amaryllidaceae family. This family includes other monocots such as daffodils, amaryllis, clivia, and agapanthus.
Allium is a large genus with over 700 species. Some estimates are higher, while some are lower. It is hard to define species of allium, and there are still ongoing debates about its taxonomy (taxonomy in the plant world is constantly changing).
Let’s get into how to obtain these popular perennials for your garden. There are a few ways to get your hands on these popular plants and a few different ways to propagate them.
This is one of the easiest ways to get alliums. They are fall-planted bulbs. Your local garden center will carry them at the same time they get other bulbs like tulips and daffodils. Another option is online or through catalogs.
You can browse through the pages and pick the ones that catch your eye. Once selected, they will be delivered according to your USDA hardiness zone so you can get them planted in time.
If you or your neighbor already have allium planted, they are easy to divide. After their foliage dies back, I will stick a popsicle stick or something to mark the placement of the plant. Then in the fall, I will take my pitchfork and lift the allium.
You will see the big main bulb. Around it, there should be some offsets. They might just be cloves or small bulbs. Grab those and transplant them into your garden. The small cloves may take a season or so to get blooming, but it’s a free way to get more plants.
If you notice plenty of foliage but no flowers, the plant might need to be divided. Lift the bulbs up and take all the tiny bulbs and cloves and transplant them or give them away.
You can purchase allium plants. Some varieties, such as Star of Persia, often come as a plant in the spring. Check your garden centers for these and purchase and plant them in the spring.
Some allium can be grown from seed. Some varieties are sterile. It will take a few years for a seed to become a flower. So I don’t generally recommend starting them from seeds.
Also, the seed will probably not look exactly like its parent plant. Bulbs are definitely the way to go unless you’re looking to grow a lot of alliums or if you’re the seed-starting process.
If you are into seed starting, collect the black seeds from the seed pods after your allium has bloomed. When starting the seeds, they will need to be cold-stratified first. Pop them into the fridge for a month prior to planting them.
Then just plant them as you would any seed. Use seed starting mix and place the seeds on the tray, keeping them evenly moist. Cover them and place them in the dark to germinate. A heat mat or on top of an old refrigerator will help them germinate. Once the seedlings emerge, place them under grow lights and watch them grow.
Make sure you harden your seedlings before moving them outside. This means introducing them slowly to outdoor life. It takes about a week, and seeds grown indoors that will transition outdoors need to be hardened off.
Start by placing them in a shady spot for a few hours and bring them in. Then slowly add more time outside and then more hours of sun. Then start leaving them out overnight. Keep them watered throughout this transition. If at any time they start wilting and shriveling, move them back to the shade or back indoors and try again.
Alliums are bulbs that are planted in the fall. To plant them, dig a hole that is three times as deep as the diameter of the bulb. Or according to the planting depth on the package. So a large ‘Gladiator’ allium bulb will need to be planted much deeper than a tiny ‘Drumstick’ allium bulb.
Dig the hole, and then I always add a small handful of bone or blood meal or a mixture of both (whatever I have on hand) into the hole.
Make sure to plant the bulb with the flat hairy side facing down and the pointed side facing upwards. Do not plant them upside down. Bulbs will find their way up and out of the soil if they are planted upside down. But that takes energy, and you want that energy spent making beautiful blooms.
Space them apart according to the package directions. I tend to plant a lot of them close together. But you can also dig a trench to plant them. Place the bulbs, so they are close. But make sure they are not touching.
Fill in the holes with soil and water them well. Then wait for them to emerge in the spring. I rarely have a problem with them appearing in the spring. Squirrels don’t like allium and tend not to dig them up, unlike tulip bulbs that they steal and eat. If you find your allium isn’t coming up, the site you chose may be too wet, causing root rot.
Not all alliums are fall-planted bulbs. Allium ‘Millennium’ is a clumping variety that is grown from a bare root or as a typical perennial plant. These can be planted at any time.
How to Grow
Alliums are an easy perennial to grow if you have them growing in ideal conditions. Let’s examine these conditions further.
Alliums require full-part sun conditions. You’ll find that full sun is usually the go-to recommendation. However, I find some full sun conditions too intense. You will find that they will fizzle out quickly in too much heat and sun.
This has to do with the quality of the sunlight. Full sun is fine, but the hot afternoon sun can be too intense. Late afternoon and morning sun are far better. If you do have your allium planted in full sun, be prepared to water them more often.
I think partial sun is the sweet spot for growing allium. Morning sunlight is great, so an eastern exposed garden would be ideal.
Alliums do not grow in shade conditions. Don’t even try. You will end up with some stringy foliage but no blooms. If you experience this, simply dig them up in the fall. Move them to a sunnier location.
Alliums aren’t too picky about soil. In an ideal world, they prefer nutrient-rich, loose soil. But I’ve grown them in heavy soil, sandy soil, soil with little nutrients. They will still grow and bloom. All I will say is the soil must drain.
They will rot if they are left in standing water. If you want a great perennial garden, I recommend amending your soil with plenty of compost, aged manure, worm castings, or sea soil. Most of your perennials, including alliums, will thank you.
If you are growing in containers, use an all-purpose potting mix. Do not use garden soil. It is too heavy for container growing.
Water your allium when you first plant them in the fall. In the spring, they won’t require much extra water unless it is extremely dry in your area. If planted in full sun, you will need to provide extra water so they last longer.
I have a drip hose snaking through my perennial garden, and I turn it on for a couple of hours a week (if we don’t receive enough rainfall).
In containers, water to keep them evenly moist. Don’t let them dry out, but don’t let them get too soggy. Make sure you have proper drainage holes in your containers to drain excess water, so they do not rot.
Climate and Temperature
Alliums are hardy in zones 3-8. They require a period of cold dormancy in the winter.
If you are growing in containers, leave the containers outside or in an unheated garage or shed. You cannot bring them indoors or into a heated garage or greenhouse.
Asides from the bone and/or blood meal I add to the hole when planting my bulbs, I do not fertilize. But I do top-dress all my garden beds with organic matter in the fall. This provides all the nutrients your garden needs all summer long.
It doesn’t have to be much, just a thin layer. The rain and snow melting will allow the nutrients to seep in. This can also be done in the early spring.
Alliums need a bit of maintenance in your garden. They will sprout and grow in the early spring. You will get spectacular blooms, and then the plant will die back.
Right when the bloom starts to open, the bottom foliage will already be starting to die back. This brown foliage is unattractive in a spring garden. I recommend trying to cover it with other plants so all you see is the flower rising from its stalk.
I like to use hostas for this, but hydrangea, sweet woodruff, and peonies (and lots of other plants) can hide the bottom foliage.
If you want to get into the realm of high maintenance, you can take a sharp pair of scissors and prune any brown tips on an angle. Once the foliage has completely died back, you can pull it.
After allium blooms, I tend to leave them in my garden. The seed heads are interesting. When I’m going through and weeding my garden, I will give them a gentle tug. They easily release when they are ready to come out. Don’t pull too hard, or you’ll pull the whole bulb out. That means it’s not ready.
Now that you understand the mechanics of allium care let’s move on to design.
There are lots of ways to add alliums into your garden. They can be added as pops through your garden beds. I recommend planting small clusters of three, five, or seven bulbs. Odd numbers are more visually pleasing.
They also look good in rows for a more formal look. I recommend a large variety such as ‘Ambassador’ for a stately look. Plant them in rows with another plant at their feet to cover the bottom foliage. A low boxwood hedge works great.
Some of the shorter varieties, like ‘Schubertii’ make great border plants. Plant these stubby flowers up front along garden borders and pathways.
Alliums also do well in containers. If you are short on space or want to do a special spring container, alliums work great. Plant your bulbs in the containers in the fall, leave them outside, and they will emerge in the spring.
There are lots of different varieties of alliums. They come in different sizes, colors, and textures. You will be sure to find one that suits your tastes and needs in your garden. Go to a specialty garden center or browse garden websites and catalogs to get your hands on some of the more unique varieties.
‘Globemaster’ is the big boy of all the alliums. The flowers rise 4′ in the garden. They have big tight purple orbs of flowers. What makes this variety stand out is the size of those blossoms. They reach up to 10″ in diameter! They put on a great show in the spring.
‘Purple Sensation’ is the common garden variety. I find bags of these bulbs in almost all the garden centers in the fall. They grow up to 3′ high and have nice dark purple orbs of flowers.
‘Mount Everest’ is similar to ‘Purple Sensation’ in size and shape, but with one dramatic difference. The flowers are a creamy white color. I like to mix a few of these in with purple varieties to add a bit of depth and dimension to the garden.
‘Party Balloons’ is a fun variety, great for containers. This is a single bulb that produces three stems with three separate flowers. The flowers are all slightly different heights, so it creates a perfect bouquet in a container.
Alliums look best when they are part of a garden. They look great with lots of perennials and shrubs. Here are a few of my favorite companion plants to pair them with.
Hostas and alliums are a match made in heaven. Alliums are up and out of the ground in early spring. I think they are quite lovely at this time. Some varieties have little reddish-pink tips.
Then as they grow and the flower stem starts to emerge, the bottom foliage will start to die back. It will then slowly start to turn brown. Luckily this is around the time hostas get up and out of the ground. As the allium bloom, the hostas will be out and able to cover the dying allium foliage.
I love large varieties of hosta, like ‘Sum and Substance’. They will really grow up and hide the bottom foliage on an allium.
Low hedges give a really formal look and will hide the bottom of your allium. It’s really up to you and your zone to decide which low hedge will work best. Boxwood, rosemary, or cotoneasters all come to mind.
You can really prune these plants into perfect tight low hedges. Plant your allium in the middle. Large ‘Globemaster’ allium planted behind them will provide a real whimsical and dramatic look.
Hydrangeas are another large plant that can cover allium. The big balls of hydrangea flowers are the perfect companion for allium. For lower hardiness zone gardeners, Annabelle hydrangeas are a perfect choice.
They bloom later in the season and will fill in and cover the spots where the allium have bloomed and died back.
Sweet Woodruff is a fluffy ground cover plant. It has small glossy green foliage. In spring, it is covered in white star-shaped flowers. It looks great with alliums rising up through it. It’s a whimsical plant pairing.
Pests and Diseases
Alliums rarely have problems with pests or diseases. This perennial is naturally resistant to deer and other critters because of their pungent garlic odor, making them a great bulb choice. Slugs and snails also tend to avoid them.
But there are a few pests and diseases that can affect your alliums. Here are a few of them and ways to treat them.
Allium Leaf Miner
Allium leaf miners will destroy your plants. If you notice streaks of white, little dots in a line, this is a sign of allium leaf miners.
This is an adult leaf miner. The female will then lay eggs in the holes that she produced in the plant. Hatched larvae will feed on the stems and leaves of the plant.
Once they have these puncture wounds, it leaves them prone to bacterial infections like rot, which will cause them to topple and die. These little flies with orange heads can do a lot of damage.
Cleaning the foliage away from the plant after it has died back can help prevent the leaf miners from getting into the foliage. If you see signs of them, spray with neem oil or an insecticide to help prevent them from laying eggs.
A common Allium disease, bulb rot can cause problems. This bacteria will rot your bulbs, and then the whole plant will turn to mush and rot away. It is best to prevent this from happening. Make sure to plant your allium in its ideal conditions.
That is full-part sun and nice loose soil that can drain freely. Bulbs in wet soil are almost certain to develop rot. Unfortunately, there isn’t much to do once your bulbs have rotted. Either amend the soil, so it drains.
This includes adding coconut coir or peat and compost to loosen the soil. But if it’s just a boggy spot in your garden, find a different planting location.
I do find that sometimes allium foliage can get powdery mildew. The foliage dies back quickly and isn’t the main feature of the plant. So from that standpoint, it isn’t much of a problem.
However, it can spread to other plants and become a bigger deal. Start by removing all the foliage that has died back from your allium.
Do this as soon as possible if they have powdery mildew. You can also spray the foliage with a fungicide formulated for powdery mildew if this is an ongoing problem. To prevent powdery mildew, try watering your plants directly at the soil line instead of overhead. Wet foliage is more susceptible to diseases, including powdery mildew.
Frequently Asked Questions
Do Allium bulbs multiply?
Yes! Allium bulbs multiply underground. If you notice your plants aren’t blooming, but shoot up lots of foliage, it is time to split them. Lift the bulbs with a pitchfork or spade in the fall. Move them around the garden or give them away.
What does an allium look like when it starts to grow?
Alliums are quite pretty when they first emerge from the ground. They are monocots, so they have grass like blades of foliage. Sometimes they will have reddish purple tips. Then as they mature a long stalk will grow and it will burst open.
When do alliums bloom
Alliums bloom in the spring. However there are exceptions. Allium Millennium comes to mind. It is a clumping variety that blooms later in the summer. If you add these to your garden you will extend the blooms in your garden.
When should I plant allium bulbs?
Allium bulbs should be planted in the fall. You can plant them in the early spring but they won’t fully develop their blossom. Fall planted bulbs should bloom the following spring no problem. This also happens to be when they are available to purchase from garden centers.
How many flowers does one allium bulb produce?
This is variety dependent. But for the classic allium that has a long stem and purple ball of flowers (e.g. ‘Purple Sensation’), one bulb will make one flower.
Do alliums like sun or shade?
Alliums need sun in order to bloom. They will not bloom in shade gardens. Part sun conditions, in my opinion, is the sweet spot for for these perennial bulbs. Protection from the hot afternoon sun will prolong the blooms and they will require less frequent watering.
Alliums are one of my favorite flowers in a spring garden. I find a place to add them into almost all of the gardens I tend to. When you have many garden tasks in the spring, it can be a burden to get everything done. But things slow down in fall, and planting alliums is a great fall project.
Unlike some perennials that take years to establish (peonies!), an allium bulb, if planted correctly in ideal conditions, will produce blooms the following spring. They are unique and wonderful flowers to add to the garden. Have fun playing with different varieties and creating a landscape that you love.