11 Tips For Growing Allium in Pots or Containers
Are you adding ornamental allium to your container garden this season? These purple flowering plants are extremely beautiful and easy to grow. In this article, certified master gardener Laura Elsner shares her top tips for growing ornamental allium in pots or containers this season!
Alliums are one of my favorite perennials. They are unique with their wands of flowers hovering over your spring garden. These popular fall-planted bulbs are extremely easy to grow.
Simply plant them in the late fall and watch them grow in the spring. If you are short on space, live in a condo or apartment with no yard, or just want to bring these beauties closer in your space, consider planting them in containers.
Alliums are actually fairly simple to grow in containers. Move forward with the following tips, and you’ll have them growing in containers in no time.
Plant at the Right Time
Allium bulbs are best planted in containers during late autumn for spring blossoms. They do require a period of cold dormancy in order to grow in spring.
You can plant them in early spring, but you will end up with less spectacular blooms, which isn’t what you’re after in a container. So put this task on your fall to-do list. This also is when allium bulbs come into stores and are available to order online and in catalogs.
You can plant them in containers and then just leave them off to the side in the winter. If you live in an area with harsh winter (zones 3 and 4) try placing them in an unheated garage or shed. Just make sure to check on them periodically, so they don’t dry out completely.
Another option is to purchase them in the spring as plants from the garden center. They can be carefully transplanted into containers. Some varieties, such as allium ‘Millennium’ are rhizomes (this variety forms a clump). This variety can be planted at any time.
Choose the Right Container
Your container is important when planting alliums. You will want a container big enough that the bulbs won’t be touching in the container (I’ll get into varieties and bulb size in #7). You also want to be able to plant the bulbs as deep into the soil as you would in the garden.
Another consideration is the material of your pot. Terracotta pots have plenty of air flow. They also can absorb excess moisture and release it when the soil dries out. Allium likes evenly moist but never wet soil. Terracotta is a good choice for a container.
Plastic, metal, and fiberglass containers are fine too. But depending on their color and the location you have them in, they can absorb sun and really heat up. This will mean more watering and perhaps shorter-lasting blooms.
I will say, whatever material you choose, make sure they have adequate drainage. Gravel in the bottom of a pot doesn’t count. They need a hole or holes in the bottom, for excess water to drain. Or else the bulbs will rot.
I don’t recommend placing gravel or shards of pots to block the bottom. A nice large opening at the bottom is necessary. You can put a piece of mesh over the hole if you don’t want the soil to come out at the bottom.
Pick The Right Container Location
When your allium is growing and blooming, you will want to make sure that they are getting part-full sun. I think eastern exposures are ideal. They will get the gentle morning sun and then some shade in the heat of the afternoon. This will be the spot where your allium blooms will last the longest.
Too much hot sun and your allium blooms will fizzle out fast. They will also need to be watered a lot more often. On the other side, too much shade and your allium won’t bloom. You might get some stringy foliage but no blooms.
When overwintering your allium, it does not matter where you place them as long as they are kept in 40F (4C). Do not bring your containers indoors or into a heated garage.
Use The Right Soil
Allium likes loose free draining soil. When planting into containers, garden soil does not work. Even if you have alliums growing in your garden, the soil will not work in containers.
An all-purpose potting mix is best. This is light and fluffy and meant for containers. It will absorb and release moisture as needed.
You can top-dress potting soil with some compost or worm castings to replenish the nutrients in containers if they’ve been in them for more than one season. When you water, all those yummy plant nutrients will seep into the plant.
Plant Depth Based on Variety
There are a few things to know when planting allium bulbs in containers. The first thing is depth. The variety of allium will determine the depth. The general rule of thumb is to plant the bulb three times as deep as the bulb’s diameter.
This is important because not all allium bulbs are the same size. Some of the large alliums (e.g., ‘Ambassador’) have fist-sized bulbs and will need to be planted much deeper than a typical garlic bulb-sized allium (e.g., ‘Purple Sensation’).
There are even smaller varieties (e.g., ‘Drumstick‘) that have marble-sized bulbs. The size of the bulb will determine the planting depth and the size of the container you will need.
The next thing to know when planting allium is which way to plant them. An allium bulb is essentially a garlic (same genus). They will have a flat bottom with hairy sprouts on the bottom. Then the top will be a point. When planting your bulbs, make sure the flat hairy side is facing down and the pointy side is facing up.
Finally, make sure you are spacing your bulbs in the container. They can be close, but they should not be touching.
To plant, start by filling the bottom of your container, leaving the amount of room for the required planting depth of your bulb. Lay the allium bulbs flat side down, not touching. Then pour the rest of the potting mix onto them to cover them. Finish by giving them good deep water.
Stick to a Strict Watering Schedule
Alliums in the garden don’t really require much extra water. But containers are a closed system so you will have to pay attention to watering.
After you first plant the bulbs, water them in well. In the winter months when they are dormant, they will need less water. Make sure they don’t dry out completely. But also watch that they don’t get too wet and rot.
In their active growing period, just ensure that they are evenly moist. The frequency will depend on factors such as the location of your pot, the size of the pot, and if it receives rainfall. I would check on them every other day or so until you get into a groove and know how often to water. Allium will get droopy when they need a drink.
Do not overwater. They will rot and turn to mush. Stick your finger into the soil to determine if it needs watering.
Pick a Container Sized Variety
While any variety of allium can be planted into pots, I find some varieties lend themselves to container growing better than others.
Large varieties such as ‘His Excellency’, ‘Globemaster’, and ‘Gladiator’ are great for gardens. However, these are really tall varieties, and their bulbs are large. You will need very large containers in order to get them planted deep enough.
Regular-sized allium such as ‘Purple Sensation’ are good choices for containers. They have smaller flower heads on long stems. Or try a white variety like ‘Mount Everest’ for a formal green and white display. If you are looking for something a little different for containers, here a few varieties that are shorter and sturdier.
This variety is great for containers because it is essentially three alliums in one bulb. ‘Party Balloons’ sprouts three separate stalks of flowers out of a single bulb.
All the flowers are slightly different heights, so it is an instant arrangement. The bottom foliage is also broader, which adds interest to a container.
This variety is just as the name suggests, a graceful beauty. It’s a small allium that only reaches 18″ in height. The small balls of flowers are white six-petaled stars.
Then it has purple stamens that add a perfect hint of color. The bottom foliage is grassy. It looks great in containers.
‘Drumstick’ allium bulbs are very small, and you can fit a lot of them in a container. Or you can use a small container to create a small arrangement. This variety has egg-shaped oval blooms that are a burgundy color.
‘Ostara’ is a stubby variety that only reaches 12″, perfect for containers. But despite its small size, it has large burgundy blossoms that reach 4-6″ in diameter. The foliage is broader and adds extra interest to the container.
Disguise Browning Foliage
There really isn’t much to be done while your alliums are growing and blooming. They don’t require any extra fertilizer besides the top dressing of compost material in the early spring.
As allium grow, the bottom foliage starts to emerge and then the long slender stalk will rise, and it will emerge from its bud. The whole process is lovely.
The only downside to allium is that the bottom starts to turn brown by the time the flower blooms. You have a few options to deal with this. You can trim the brown out. I will take a sharp pair of scissors and prune the brown tips. Trim on an angle, not a blunt cut, so it looks natural.
Another option is to plant a variety that has foliage that stays nicer longer. ‘His Excellency’ allium apparently stays greener longer.
Finally, another option is to plant something that will hide the browning bottoms. This is much easier to do in the garden. But it is possible in a container. Plant a hydrangea in the front of a container with allium in the back. The tall stalks will rise above the hydrangea, but the grassy foliage will be covered.
Provide Post-Blooming Maintenance
Allium is a spring-blooming perennial. As with most perennials, it grows, blooms, and then dies back. Alliums die back very soon after they bloom. So, what happens next?
I like to leave my alliums as long as I can. The blooms may have finished, but the spent blossom still looks good for a couple of weeks or so after. Soon the bloom will topple over or start to look bad. You have a few options.
One of my favorite options is to have containers full of allium that can be moved. Have them as spring containers mixed with other bulbs and/or spring flowers.
Let them grow, and then put them in a less visible area in the garden where they can spend the rest of the summer. Just make sure to remember to water them. If you have an irrigation system, just leave them in a garden bed to get watered.
Another option is to have your allium in a pot with other plants that can take over the show after they’ve finished. You can buy an inexpensive dracaena plant (the green spike) and place it in the hole the allium left. Then have other flowers grow around.
Or you can have them planted behind large plants, like roses or hydrangeas, that will cover the plant, and you won’t even notice they are there anymore. Remember, with these options, you will need large pots to accommodate all the roots of all the plants.
Or you can simply pull your allium out of the pot and create a new arrangement. You can always plant your allium in the garden, and they can grow next season. Or save the bulbs in a paper bag and plant them again in the fall.
Companion Plant for Color
Alliums look great in a pot on their own, but they also look wonderful when they are planted with other plants. Let’s look at some companion plants that look great in containers with allium.
Pansies and Violas
This is a perfect pairing if you ask me. The allium rises up, and the little violas or pansies grow around them in the container. Both these flowers fade in the summer, but they look great in spring. The pansies will grow up and hide some of the dying bottoms of the allium.
Sweet alyssum is another cool spring loving plant. It smells wonderful and is great for containers. It fills and spills out of pots. Sweet Alyssum will fill in the understory of the pot, and with allium in the center. When planted with allium, it’s a light, airy, whimsical combination.
Other Spring Bulbs
Grab a big terracotta container in the fall. Or prepare your containers in the fall. Add a combination of allium bulbs, daffodils, grape hyacinth, hyacinth, and/or tulips etc. Make sure to account for their height when planting.
Taller things in the back and middle then short bulbs in the front and edges. Then either move the prepared container to its spot and move it off to the side after it blooms and let it overwinter.
Or pull up all the bulbs once they bloom and die and store them in sawdust or paper bags in a dark room, and plant them again. Or plant them in the garden and get new bulbs in the fall. Let the foliage die back naturally so they can get enough energy stored to grow and bloom the following season.
Overwinter When Necessary
After your allium has grown and died back in its pot, it is ready for the winter. It is important to let your allium die back naturally. Don’t yank it prematurely. The plant is photosynthesizing and making energy to grow next year. If it looks bad, try and hide it with another plant or move the container.
Allium cannot be overwintered indoors or in heated garages or a heated greenhouse. They require a period of cold dormancy. If you live in zone 3 or 4 I recommend bringing the container into an unheated garage or shed.
The winters are too cold for allium in containers in zones 3-4. Or you can dig the container into the ground before it freezes (don’t do this with terracotta, it will break). For all the other hardiness zones leave the container out.
Don’t let the pots dry out completely, but don’t let them get waterlogged and soggy. Once spring comes, new shoots should emerge. Start watering more and enjoy your allium all over again.
If you’ve been toying with the idea of allium in containers, I say go for it. Start with a less expensive variety and experiment. You’ll be a pro in no time. Use these tips as your guide. They are an unexpected surprise in a container, and they will get noticed by everyone visiting your garden!