I love it when the seasons change. During the approach to each equinox, I look forward to feeling a change in temperature, seeing the shift in the way sunlight falls, and watching the many ways that plants react to a new season. This year, our typically crisp autumn weather hasn’t been as cool as some years, but the nights will likely dip below freezing this week. With those colder temperatures, many more plants will enter dormancy or die back and, when we look at our garden beds, it's obvious that a seasonal change is afoot.
What to do? Should all those fallen leaves be whisked away in big dump trucks? Should those dead stems be cut down to the ground? Should the annuals get ripped out and tossed into the compost? As with many things, the answer I give to these questions is: it depends.
To find the best answers to my autumn clean-up questions, I start with a few more questions. How is the area of the landscape used? What is best for the health of the plants in the area? What is the ecological impact of any gardening action in the area? What are the aesthetic objectives of the area?
A residential turf lawn, a soccer field, and a meadow are all open spaces, but they have different uses and, therefore, different care needs. A rain garden at the edge of a suburban sidewalk, a residential garden bed with perennials and spring bulbs, and a bed of annuals may have similar ornamental uses, but each could proffer a very different ecological impact and have different plant health needs. Some landscapes have strict aesthetic parameters—housing associations and historic gardens come to mind—while others can be kept—or unkempt—according to the wishes of the property owner.
Dead plant material is full of potential nutrients for the growing seasons to come and can provide important habitat for beneficial insects and other fauna. Conversely, a thick layer of fallen leaves can smother plants (including turf grass) and a bed of dead-looking plants might not fit into everyone’s ideal of “winter interest.”
At Reeves-Reed we try to find a balance between all the questions I pose above. Our turf grass needs to be clear of leaves for visitors to safely walk, but we try to retain the fallen leaves for mulching planting beds. Some summer annuals will be turned to the compost pile when it’s time to plant seasonal bulbs in their stead, while others have already been dug up and prepared for winter storage.
The questions of when and how to cut back perennials is answered on a case-by case basis. The health of the plant is considered first, then factors of aesthetics and ecology are given more or less weight, depending on the location of the plant. If there is any suspicion that dead plant material might harbor disease over the winter—peony leaves are a bit notorious for this—then that plant should be fully cut back and all material sent to the dump. Other plants, when dormant, may have interesting seed heads that provide winter interest and may be a food source for migrating birds. Additionally, the stalks and fallen leaves of many dormant perennials serve as shelter for beneficial insects, which promotes greater biodiversity and supports a healthy ecosystem.