A Little off the Top
Growing season is well underway and it is time for some plants to get a little haircut!
Think back to last season… seems like a long way away now, but if you flip through the files in your memory banks, perhaps you remember some floppy perennials in your garden? Ones that grew nicely at the start of the season and then upon flowering, or after a driving rain the plants decided to split open in the middle and lie down on the ground in all directions?
Perhaps this is ringing a bell and you are now thinking “ah, yes… those plants drove me CRAZY!”
Aside from staking up floppy plants (something that we will do later in the summer), there IS a solution for some plants to prevent ‘the flop’. It is a little technique called ‘cutting back’ (or ‘pinching’ if only the tips of the plant are removed).
The Technique
Essentially, ‘cutting back’ is exactly that- cutting back the stems of a perennial. Not all perennials can tolerate a prune like this but there are some common ‘floppy’ perennials that can, such as Sedum…
A clump of Sedum before and after being cut back (along with the clippings to illustrate how much of a ‘haircut’ the plant got!)
I also used this technique on some catmint (Nepeta racemosa ‘Walker’s Low’)…
Catmint before and after being cut back.
So how does ‘cutting back’ combat ‘the flop’?
By cutting down the stems of a perennial, the plant is forced to direct it’s growth elsewhere- which would be the next remaining buds on the stem (shown in the photo of the catmint below). When these buds begin to grow, the plant ‘branches out’ from these new growing points, ultimately leading to a fuller/bushier plant. The denser plant allows for the stems to rely on each other for some support to stay upright. [Now sing with me… “Lean on me… when you’re not strong…”}
A catmint stem before and after being cut back. The red dots show the new growing points for that stem. The cutting back of the stem ultimately forces one stem to branch into two.
Cutting back a perennial also leads to a shorter overall stem height. By forcing the plant to branch, the plant’s energy must be used to grow a greater number of stems. I like to think of it as each stem vying for the same resources. With more stems trying to grow, there is less energy available for each stem- which ultimately leads to a shorter stem height (as well as smaller flowers).
It is the combination of a shorter height and fuller plant that translates to a sturdier perennial that can resist flopping over!
An Added Benefit
Cutting back perennials has another consequence and that is a delay in flowering. Cutting back can be considered a ‘set-back’ to the plant, so it should be no surprise that it will take time for the plant to rebound from the prune and begin growing again from new buds. It must do this before it can actually attempt to flower! The time it takes the plant to rebound from the prune is responsible for the delay in flowering.
On the surface, this delay of flowering could be seen as a negative consequence but it can actually be used to your advantage! First of all, in the case of both the Sedum and the Nepeta, I have not pruned all the plants in my garden. That way some of the clumps will flower at their usual time and the pruned ones will flower later. (For example, two weeks after the initial prune of the catmint, the unpruned clump is ready to flower, the pruned clumps are still rebounding from being cut back.) The result? A longer overall flowering period for these perennials! This doesn’t just translate to a longer floral display for my appreciation. These plants happen to be located in a pollinator-friendly garden which means the longer bloom time presents a longer period of time when the ‘floral buffet’ is open for these important creatures. Dig in!
Catmint in a pollinator garden. The unpruned clump is on the verge of flowering, the other two clumps have branched out and begun growing from their new growing points (shown by the arrows). These two pruned plants will be delayed in their flowering.
So far, I have only cut back Sedum spp. and Nepeta this year. Some of the more common perennials ‘on deck’ for a haircut include:
Balloonflower (Platycodon spp.)
Aster
Chrysathemum
Beebalm (Monarda spp.)
Russian Sage (Pervoskia atriplicifolia)
Some other perennials that can be cut back to prevent ‘the flop’ (clockwise from top left): Platycodon spp. (balloon flower), Chrysanthemum spp., Aster spp., Veronica spp. and Echinacea spp. (speedwell and coneflower)
For more information on this topic, check out the amazing book by Tracy DiSabato-Aust called The Well-Tended Perennial Garden. (2006, Timber Press Inc.). In this book you will find a LOT more detail with respect to pruning perennials, as well useful lists that outline what perennials can tolerate pruning and at what time. Some all around good bedtime reading :)
More posts on perennial pruning in the weeks ahead!