I have a bit of a love-hate relationship with cosmos, but thankfully, the love ultimately prevails.
My main issue? The harvesting. The stems are so thin, and the foliage is so bushy that it’s often awkward to find the right spot to cut. Over the years, I’ve started to enjoy harvesting them more, especially when I know I’ll end up with a huge bucket full, rather than just a few stems. Despite this challenge, cosmos are truly one of the workhorses of my garden.
Cosmos are easy to start from seed and come in a wide variety of beautiful colours. They come in singles, doubles, cupcake shapes, and more. Plus, they’re incredibly easy to save seeds from! (Though I’ve learned the hard way about the dominant outline trait—more on that below!)
No matter how they turn out, I love having a 40-foot row of cosmos. Keep reading for my best tips and tricks for starting, growing, harvesting, and saving cosmos!
How to Seed Start Cosmos in a Short Season
You can either start cosmos from seed or direct-sow them, though I don’t recommend direct sowing in a cold climate and short growing season. If you’re gardening somewhere with early frost or your yard runs cold, you risk not getting any blooms because they’ll take too long to mature.
If you’re somewhere warmer, just direct-sow them.
If you choose to seed-start your cosmos, you can do this anywhere from 4-10 weeks before planting out. 6 weeks is optimal, and 10 is extreme—I did start some seeds at 10 weeks this year, and somehow everything worked out really well. They started blooming in my garden when I started writing notes for this blog post in the third week of June!
How to Harvest Cosmos
Cosmos are cut-and-come-again, and when mine are in full production, I can aggressively cut them and then have blooms again in two to three days. They’re the gift that keeps on giving!
Make sure to cut as long a stem as possible, because if you keep cutting short stems you’ll get short new stems. I learned that the hard way when I was trimming the ones that were starting to die, and I was getting little itty bitty stems. So learn from my experience and always cut long!
Their vase life is not the most fantastic, but you can usually get at least five days. Just make sure when you pick your cosmos the centre has no or little-to-no fluffy parts. My favourite varieties to arrange with are the Double Click Mix and the Cupcakes Blush.
How to Seed Save Cosmos
I mark my favourite varieties with painter’s tape to save from seed, and then I let the bees do their thing. If I feel like the seeds are going to fall off and I’m not ready to collect them, I’ll put a mesh bag over the flower. The seeds are not ready until they are very easy to take off.
I used to argue that I often prefer the cross-pollination I get when saving seeds more than the legitimate varieties themselves. Little did I know that the outline trait in cosmos has extremely strong genetics, which tends to dominate everything else. Therefore, after this year’s experience growing cosmos from saved seeds, I retract my initial opinion!
The outcome was not all bad, but the outlined cosmos overwhelmed my garden, and they are not suitable for wedding orders, which make up the bulk of my business! This was not the cost-saving measure I’d hoped it would be. However, many people have loved these outlined cosmos, so I plan to sell my saved seeds under the name “Promiscuous Cosmos.” If you buy these seeds, you get what you get!
I also have to mention that the Apricotta genetics seem quite weak. I only have two miserly stems this year that resemble Apricotta, and I saved a bunch of seeds of that variety! I planted a ton of them, expecting a lot more of them to turn out… The result? Sad.
Cosmos are also prolific self-seeders, so don’t be surprised if you find a couple of volunteers where you planted them the previous year. I let my volunteers live, and I dig them up and move them to where I’m planning to plant my cosmos in that year in my garden.
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