After I wrote a post about cutting blue mist spirea to the ground in spring as part of spring cleanup, one question I received was, “Will cutting it to the ground delay flowering?”
Be sure to check out this video about how to cut back or prune blue mist spirea in spring.
July and August are the height of blue mist spirea’s bloom time. So let’s see what actually happened.
Cut to New Growth
Here are two blue mist spirea shrubs that were only cut to the new growth in spring. The day this photo was taken, they had been in bloom for about one to two weeks. Also notice this pruning method maintained the maximum size of the shrubs. They are large and full.
Cut to Ground Level
Here’s a healthy, vigorous blue mist spirea that was cut to the ground in spring. In the photo, which was taken on the same day as the photo above, you’ll notice that the flowers are just beginning to open.
So, the pruning method did indeed delay its bloom. How much later? About two weeks. Also, notice the shrub itself is a little smaller than the shrubs that were cut to the new growth. It’s about 6-10 inches smaller on all sides. However, it has a nice, full branching pattern with lots of flowers just about to open. You could prune it to the new growth in future years to allow it to regain its full size.
Cut to Ground Level in Shade
Here’s a dark knight spirea that is growing in a much shadier environment. I cut it to the ground this spring, and it has not fully recovered its original size, nor has it bloomed. It has a few flower buds on it, but I don’t expect it to bloom much this summer.
Cutting it to the ground did not kill it, but its recovery has been much slower. I’ve seen this same reaction on multiple spireas, both blue mist and dark knight, in shady locations that were cut to ground level. In fact, the slow recovery also occurred when I cut some alpine currants growing in the shade of a building to the ground.
It will take 2-3 years for this plant to regain its full size and entire set of flowers. Ultimately, there’s a more pronounced drawback to this pruning method for spireas (and other deciduous shrubs) growing in shade.
So, even though cutting to ground level works well on plants growing in full sun, you might want to take into account the required recovery time for plants growing in shadier sites. Keep in mind dark knight spirea blooms a little later than the blue mist cultivar normally. In my yard today, there’s a blue mist spirea in full bloom, while the dark knight spirea is full of unopened flower buds.
To sum it up, here’s what I’ve learned about pruning blue mist spirea during spring cleanup. This same information generally applies to dark knight spirea as well.
- To maintain a shrub at its largest possible size, prune only to the new growth.
- To reduce a blue mist spirea’s size and rejuvenate its branching pattern, cut off all the stems at ground level before the new leaves emerge in spring.
- Even if a plant is growing from one central stem, and you cut the main stem with a pruning saw at ground level, it can recover.
- Cutting a healthy blue mist spirea to ground level will delay its flowering by about two weeks.
- Dark knight spirea naturally blooms a few weeks later than blue mist spirea.
In addition, for plants growing in shade:
- If you cut a blue mist spirea growing in a shady location to the ground, it will take it 2-3 years to fully regain its full size.
- The shadier the location, the slower the recovery.
- If you want to rejuvenate the branching pattern of the plant, the time for recovery may be worth the cost of the recovery time.
- For plants with an attractive branching pattern, it’s probably better to prune them only to the new growth.
The great thing about plants is, as long as you keep experimenting, you’ll never stop learning!