If you grow dahlias (and I recommend you do, if you have a sunny spot available), the best way to keep them blooming is to continually cut the flowers.
Either pick them for cut flower arrangements, or leave them on the plant to enjoy in the garden but then remove the flowers as soon as they start to get past their prime. This process of removing the spent flowers is called deadheading.
There are a couple reasons to deadhead, but the main one is that it avoids having the plant waste energy trying to make seeds, which leaves it more energy to produce new flowers. It also makes the plant look better and gets rid of hiding spaces for earwigs and slugs (who both seem to love aging flower petals).
Removing the old flowers can be done with secateurs or scissors or, for small to medium size dahlias, just by snapping the old blooms off with your fingers.
Is it a bud or a spent bloom?
Some people have difficulty telling the difference between a spent dahlia bloom and a new flower bud, especially once the petals have fallen off the old flower. The two are somewhat similar, but once you realize what you’re looking at, it’s easy to tell the difference. Let’s compare a bud and a bloom on one of my favourite small flowered red dahlias.
This is the bud of a dahlia flower. See how the end is flat, and it looks like it’s all packed compactly together, ready to explode with petals? It looks all closed up, like it has not been opened yet. Do not cut this off.
Spent Dahlia Bloom
This is a spent dahlia bloom. The end is somewhat pointy, and it looks like a party cracker that’s already exploded—it’s finished. Remove it.
This is also a dahlia bloom from the same plant that is past it’s prime. It’s pretty in a decaying way, but it needs to go to make way for the next batch of flowers.
I’ve been taught to snip dahlia flowers off long before they get to this point. Not only will the overall plant look better, it will spur on more fresh blooms sooner.
The dahlia in this picture (also from the same plant as the others above) is still quite fresh (please ignore the little nibbles on the ends of the petals–darn earwigs!), but the yellow centre is starting to show, so it has started on a downward trajectory. When dahlia blooms are at their peak you can’t yet see the centres.
To the right of the flower is a bud that is just about to open–you can tell it’s a bud because the end is more flat than pointy, and it still looks taut. It’s ready to take centre stage as soon as the other bloom finishes.
I don’t have a photo of this particular red dahlia at its peak, but I can show you another dahlia that is looking perfect in my garden today:
Isn’t that an amazing flower? This is dahlia ‘Cafe au Lait’ and it’s still very fresh. I hope it lasts this way for a few days, although it’s very hot here this week so we’ll see. However, there are many buds on the plant, so it looks like it will be a gorgeous August in this corner of the garden!
The Bottom Line
We only grow dahlias to see their amazing flowers, so investing a minute to check them over every few days and deadhead them is a worthwhile investment of gardening time.