Perennials: to chop or not?

Well it seems as though the gardening season is progressing at an alarming rate- is it really October??? We are now on to fall gardening tasks, and one of the main tasks is cutting perennials back (not to be confused with pruning trees and shrubs which I addressed in my previous post, Temper your Enthusiasm). At this time of year, I am often asked: “what should I cut back”? I am going to try to answer this question as concisely as possible in this post (no promises).

Before getting into the nitty gritty, however, I should first start with the other question that I am often asked which is “when should I cut back my perennials?”. In general, I wait until things are well on their way to dying back on their own. Right now, plants are gathering up some last rays of sunshine (as are we!) and beefing up their energy reserves in their root systems to help them survive the winter and have the ability to flush out new growth in the spring. Letting perennials go through this natural process allows the plants to properly prepare for winter. Usually when the leaves have turned colour (which is a sign that the plant is no longer photosynthesizing or making energy) is when I start whacking things back; this is usually (but not always) shortly before or shortly after the first frost.

What to Cut Back

Now… the all important question, what should we be cutting back? Using these 6 questions about your perennials can help point your secateurs in the right direction:

1) IS IT EVERGREEN?

Let’s face it. We don’t always grow perennials for their floral display. Take Heuchera (coral bells) for example, many cultivars of this perennial are not winning any awards for blooms- A+ for effort, but no awards. So what does this plant have going for it? Foliage! Not only do Heuchera come in all sorts of gorgeous foliage colours, the leaves of coral bells persist year-round. They are evergreen (or ever-purple, or ever-chartreuse or ever-pink…). Other examples of perennials in the evergreen category include various species of Helleborus (Lenten rose or Christmas rose), Bergenia, and Yucca. Additionally, there are also some perennials, such as Leucanthemum superbum (shasta daisy) whose flower stems die down while their basal foliage remains evergreen. So as the saying goes ‘if you’ve got it, flaunt it’ and these plants have got it…foliage in the winter, that is! Leave these perennials standing tall! Sure they may look a little ratty come spring (depending on the kind of winter we are served and the growing conditions that the plants are subjected to) but the fact of the matter is that they have the potential to look nice, even during the winter months. In areas with unreliable snow cover (ahem… southern Ontario) this can be a really nice addition to the garden.

Evergreen perennials (closckwise from top left): Bergenia sp., Heleborus sp., Heuchera sp., and the basal foliage of Leucanthemum sp.

2) DOES IT RETAIN IT’S STRUCTURE?

Some perennials, such as many ornamental grasses will retain their structure well into the winter months. These perennials will not only add structure to the garden but some gorgeous texture too (see ‘ornamental features’ below)! Other perennials such as Hosta spp. will essentially turn to mush come the first hard frost, while Polygonatum spp. (Solomon’s seal) will drop it’s leaves and loose it’s graceful form in the process. In any case, I am going to make the assumption that no one finds an indistinguishable mess of mushy leaves to be attractive. If your plants seem to crumble as soon as the cold weather hits, cut them back! It will be one less clean-up job to do in the spring and your winter garden will thank you for improving her aesthetics!

The hosta- a beautiful addition to the shady garden, absolutely useless in a winter garden.

3) IS IT WOODY?

Some perennials develop woody stems such as Perovskia atriplicifolia (Russian sage) or Lavandula (lavender). These are guaranteed to retain some structure in the winter and pruning for these two perennials is best left to the spring anyway. Leave them up and enjoy having some added structure to your garden!

4) DOES IT HAVE ORNAMENTAL FEATURES?

Beautiful texture? Ornamental seed pods? Pretty dried flowers? These are all features that look oh so beautiful when touched by a frost or coated in a light dusting of snow. Remember- winter is a beautiful season, if a plant has something that can help capture this beauty, then let it be!

Ornamental grasses and perennials such as bugbane, Sedum and Joe Pye weed have seedheads that capture a dusting of snow beautifully. *Remember, if you have a plant that tends to seed itself prolifically, you may want to chop the flowers before they go to seed*

5) DOES IT HAVE WILDLIFE VALUE?

Many perennials produce seeds valued by wildlife (especially birds); some of the more common ones include species of: Echinacea (coneflower), Rudbeckia (black-eyed Susan/gloriosa daisy), Sedum (stonecrop), Eupatorium (Joe Pye weed and boneset), Helenium (sneezeweed) and Heliopsis (false sunflower). Leave these perennials standing over the fall and winter months and you can feel good about providing a food source for our feathered friends.

Some perennials with wildlife value (clockwise from top left): black-eyed susan, stonecrop, coneflower and sneezeweed

6) IS IT DISEASED?

Did you notice anything funny on the leaves of any of your perennials this year? Perhaps a white fuzzy coating or little rusty pustules or unusual blotches? If you suspect that a perennial in your garden was diseased, it is best to cut it down (or even dig it out). Often diseases will overwinter in the garden on diseased plant material; this can become a source of infection for the next season. Cut anything suspicious down and DO NOT compost it. If it is a re-occuring problem, it may indicate that the plant is not growing in its optimum conditions (stressed plants are more prone to diseases) or it is a problem that the perennial is particularly susceptible to. If you have plants that seem to be hit by disease year after year, it may be time to think of some more robust replacements (an excellent task for the winter!).

Even though this Phlox would retain some structure over the winter, it is diseased and should be cut down.

OK OK, so that may not have been overly concise but I hope it helped! Remember- if you are not sure what to do with a certain perennial, you can always leave it alone to see how it fares the winter months. It can often be surprising what plants look attractive in the winter. So don’t be too hasty in chopping down all your perennials- right now you are the designer of your winter garden!