Contributing editor Steve Silk replies: Cleaning up the garden in fall is worthwhile only if you want a healthier and more attractive garden, a bigger compost pile, and a jump on the spring season. So I try to make time for it every year in late November or early December.
The most compelling reason for a fall cleanup is that it helps keep the garden free of pests and diseases. All kinds of insects, critters, and unwelcome organisms can overwinter in rotting foliage matted on the ground. Iris borers, for example, are wormlike critters that hide away for the winter in iris foliage, particularly that of bearded irises (Iris germanica cvs.), only to increase and unleash an onslaught the next season that can eventually wipe out an entire planting. And fallen, rotting peony foliage can harbor botrytis, a fungal disease that can cause, at the very least, misshapen, blemished flowers. Both problems are easily avoided by cutting down all iris and peony foliage in late fall and removing it from the garden.
Basically, I try to get rid of everything that falls or flops to the ground. If nothing else, it can provide shelter for voles and other rodents that might feast on my perennials during the lean winter season. I’ve heard of folding foliage over a plant’s crown to protect it during winter dormancy, but I’d never try that on a plant that might be prone to damage from winter wet, which I’ve found to be far worse than low temperatures for marginally hardy plants.
With all that mushy foliage gone, the garden already looks more attractive. I spare the drier, twiggy remnants of plants like Sedum ‘Autumn Joy’ or ‘Matrona’ that lend sculptural, though skeletal, form to the garden in winter. I also leave most ornamental grasses alone, as well as plants such as coneflowers and black-eyed Susans that provide winter food for birds. Most Caryopteris and Nepeta species I leave because their bare branches look attractive sticking out from a few inches of snow. My rule of thumb is to at least consider leaving alone anything that’s still standing, unless its bare branches are unattractive.
With all that junk hauled away from the garden and the seasonal bounty of fallen leaves, my compost pile grows to epic proportions by late fall. With the addition of a truckload or two of manure from a nearby stable, my heap cooks merrily all winter.
The last step of my clean up is to place a 2- or 3-inch-thick layer of crumbled leaves around anything I planted earlier that fall. I try to wait until the ground freezes to do this, but I sometimes get impatient enough to go ahead and do the job earlier. Here in Connecticut, we have lots of open winters with temperatures seesawing between freeze and thaw. The mulch helps stabilize soil temperatures and prevents plants from being heaved out of the ground.
Finally, my fall cleanup efforts are rewarded in spring, as I have that much less work to do during its frantic first few weeks. When the weather warms, I just cut back anything that needs it that wasn’t guillotined in the fall, run a rake through the beds, and I’m ready for a new season.