While monarch butterflies migrate south for the winter, the majority of native insects overwinter right here in Greater Columbus, usually hiding in plain sight. Butterflies and moths such as swallowtails, fritillaries and the luna moth overwinter in chrysalids, cleverly blending in with leaves and dead plant stalks in the garden and home landscape.
Fireflies and native bees hide in leaf litter or create burrows underground in garden areas and stay within an inch or two from the surface of the soil. Some bees spend the winter and lay eggs in natural cavities such as hollow stems of plants such as coneflower, some varieties of sedums, and even ornamental grasses. How we clean up our gardens and planting beds in the fall can have a detrimental effect on the populations of beneficial insects and pollinators in our gardens next spring. Garden Cover
Fall is an important time in lawn and landscape maintenance as many insect and disease problems encountered during the current growing season may survive until next season on or in plant debris. Cultural practices completed before winter arrives can ensure a healthier landscape next spring, but these same practices can also have a detrimental effect on beneficial insects, birds and the environment. The challenge for gardeners is knowing which plants to remove this fall, and which to leave until next spring.
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All diseased plants and any dead or rotting plant material should be removed in fall so that pathogens that cause plant diseases do not survive the winter in decaying plant material. Certain plants such as peonies, bearded iris and lilies should be cut down to a height of 3 inches to prevent harmful boring insects from overwintering in the foliage.
Likewise, any weeds should be removed in fall, hopefully before their seeds have dispersed.
Many perennials such as coneflowers, sedums, black-eyed Susans, Joe-Pye weed can provide both a place for beneficial insects to overwinter and an important winter food source for seed-eating birds such as finches. Allow the seed heads of these plants to ripen until they turn brown and split open. This will also allow some plants to self-sow, providing more flowers in your garden next spring.
Some flowering annuals such as marigolds can also provide winter cover for insects and a food source for birds, so consider leaving these plants standing in the fall if you can stomach their black appearance after the first hard frost.
There is an ecological benefit to leaving some leaves on the ground in shrub, annual and perennial plant beds and vegetable gardens as the leaves will add some nutrients and organic matter to the soil as they decompose this winter. A layer of leaves will also help moderate soil temperatures encouraging root growth of newly planted perennials and shrubs and preventing soil heaving caused by cycles of freezing and thawing.
By leaving a shallow layer of leaves in planting beds, you will be providing winter cover for spiders, slugs, worms, beetles, millipedes, mites and other organisms that provide food for chipmunks, turtles, birds and amphibians.
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However, I would be wary of leaving a significant layer of fallen leaves on the lawn as they can easily smother cool-season grasses that may not go dormant until January, depending upon the weather this winter. The best method for leaving fallen leaves on a lawn is to chop the leaves with a mulching lawn mower so that the small leaf particles settle into the thatch layer between individual blades of grass.
If you do not have garden beds in your home landscape where you can accumulate leaves for insect and wildlife habitat this winter, you might choose to allow leaves to remain on just a small portion of your lawn area, creating an insect and wildlife overwintering zone.
In the spring, wait as long as you can to clean out dead stalks and grasses in garden beds, as these may be the home of overwintering insects. Ideally, home gardeners should wait until it is time to mow regularly since it is likely that the overwintering bees will have emerged by then to take advantage of early blossoms. If possible, it is even better to wait until apple trees are blooming, because mining and bumble bees will be first to emerge and enjoy apple blossoms.
So put the pruners down, put your feet up, and grab a pumpkin spice latte instead of completely cleaning your garden beds this fall. In addition to the ecological benefits of leaving dead plant material standing, dead plant stalks and ornamental grasses also add visual interest to an otherwise barren landscape in the winter months.
Rain Fly Mike Hogan is an associate professor at Ohio State University and an educator at the OSU Extension.