Alliums and why you need to snip the seedheads off

Plant profile: Alliums

If you’ve ever wondered at the purple lollipop-like flowers, blooming amongst roses and peonies, you’re not alone. Every time I see someone encountering these flowers for the first time, they’re fascinated at their vibrant colour and perfectly round shape. These plants are alliums, commonly known as ornamental onions. They are part of the onion family, although I wouldn’t try eating them.

 

They’re easy to grow in sunny locations (6+ hours of direct sun per day), don’t need lots of moisture, and are generally considered hardy from zones 4 to 9.

 

Most alliums you’ll see in gardens are purple, but pink and white varieties also exist:

 

Very few pests and diseases seem to bother them, and they are beloved by bees and other pollinators:

 

They have two downsides, in my opinion. One is their foliage. The only time the leaves look good, is in very, very early spring, when they first emerge from the ground, at about the same time as early blooming tulips:

 

The leaves are a lovely bright green at that point. Unfortunately, by the time they bloom, the leaves are already starting to turn brown and flop. The next photo shows some of my alliums in full bloom, next to a tree peony–note that in the bottom right you can see that the foliage is already fading:

 

If you see this happening to your alliums, don’t be concerned that they’re sick or infested–the plant just doesn’t need its leaves any more and is getting rid of them. Alliums grow from a bulb, much like tulips. The only purpose of leaves is to make energy to store in the bulbs so that the plant can grow and bloom again next year. Alliums seem to be more efficient than tulips in creating energy, as they’re done with their leaves a lot sooner.

 

Even though these fading leaves are ugly, you shouldn’t remove them until the plant has completely died down. See my article on how to get your tulips to bloom again for the full explanation of why.

 

So the ugly foliage is the first thing I don’t love about alliums. The second is that they self-seed very aggressively.

 

When I first started my garden in Toronto I bought a big bag of Allium ‘Purple Sensation’ (110 bulbs maybe?) at a warehouse club and was surprised at how well priced they were. I now know that this is a warning sign: when you can get a lot of a plant for a low cost it means that plant is very easy to reproduce. Maybe too easy…

 

I planted them and was delighted with their blooms. Then the blooms matured and developed beautiful seed heads.

 

The purple fades but that lovely lollipop flower shape, swaying in the breeze above other plants, is lovely. Some people like the shape so much that they spray paint the flower heads. I saw these in the gardens of Riverwood Conservancy:

I don’t love this look myself, but everyone has their own taste.

 

 

But don’t be lulled by the prettiness. Get out your secateurs and cut off those seed heads before they ripen!

If you don’t they will spread like grass through your garden. I have literally pulled up fist-fulls of baby alliums every spring. And I’ve been cutting off those seed heads for years, ever since I figured out their dastardly ploy. If you have a meadow, that many alliums would be lovely. But if you’re trying to grow anything else alongside them, the allium seedlings will try to choke them out.

 

I don’t think all varieties of allium self-seed as aggressively as ‘Purple Sensation’. I’ve had one Allium ‘Christophii’ (a variety with a huge flower) for at least 5 years and have left the seed heads on every year–I think I now have 4 plants, all growing very close by the original one.

 

I keep one bed that’s primarily allium ‘Purple Sensation’ and weed it out from most of the rest of the garden. As the alliums finish, I fill in the area with zinnias and sometimes dahlias. This is what the bed looks like once I’ve chopped off all the allium seed heads:

It’s not pretty, but thankfully the plants will be fully finished with their leaves in another week or less, and the zinnias and dahlias will start to grow and take over the space.

 

Would I recommend planting alliums in your garden? Absolutely! They’re great plants. The Perennial Plant Association has even chosen an allium, Allium ‘Millenium’, as their 2018 Perennial Plant of the Year. Just be sure to snip off the seed heads before the seeds ripen!

4 Comments

  1. Patricia on June 17, 2018 at 3:24 pm

    Try growing Allium ‘Ambassador’ or ‘Globemaster’ . These don’t seed. Plant toward the back and grow perennials at least 2ft. tall in front. The alliums look lovely and the perennials hide the brown foliage. No more problems!

    • Barbars on March 25, 2023 at 5:33 pm

      I cut the flowering top off my mom’s purple allium last year (22) after it was finished flowering. I put that top in a bag and it is completely dried out.

      Will this produce seeds I can plant in a flower pot in order to produce a plant so I could eventually plant in the ground?

      I live in Southeastern WA in a high desert climate. July & August are the hottest months of over 100-115

      Spring has sprung here. We are seeing Temps now high 50’s – 60’s now.

      I’d like to have some of my mom’s allium to start a bed along my backyard fence line. I have no flowering beds in my yard.

      Please advise me what to do.

      Thank You.

      Barb

      • Jennifer on May 31, 2023 at 8:05 am

        Sprinkle them around, they will grow. There won’t be flowers the first year, but in subsequent years, as the bulbs gain strength (leave the foliage on them until it has completely died off–that’s what’s feeding the bulbs), you will have flowers.

  2. Teresa on April 13, 2024 at 11:51 am

    Thanks for printing this. I finally theorized that the alliums were choking out my iris, but couldn’t find any supporting articles. I now will be digging my entire front bed as I prefer my iris to the alliums. I might put some in another place where the summer perennials come up after the alliums are mostly died back.

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