by Jason Hill and Abbie Castriotta
As fall rolls through and the colors on the asters (Symphyotrichum species) and goldenrods (Solidago species) fade, it’s easy to be lulled into a sense that the growing season has finished. But that’s far from the case. Over winter, carefully managed flower gardens and yards will grow a crop of pollinators and other invertebrates for next year. These are the insects that will pollinate our gardens, and ensure a future supply of food for birds and amphibians after migration and hibernation is complete next spring. Indeed, the growing season has just begun and autumn is a critical time to think about how we can bolster insect populations around our homes.
First, fall is a great time to reassess the flowering plant diversity around our homes to ensure that blooming native plants are available as nectar resources for the many pollinators that are still active. For example, queen bumble bees (Bombus species) visit flowers through October as they gather nectar before heading underground to hibernate—ensuring your yard has blooming plants in October is an investment in future bumble bee populations. As of this week, local nurseries still have actively-blooming, native plants such as asters and goldenrods—the two groups of plants that likely support the most butterfly and moth species in our New England landscape, according to Entomologist Doug Tallamy at the University of Delaware. Many native flowering plant species require cold stratification for their seeds to germinate (e.g., Canadian Bunchberry [Cornus canadensis], goldenrods, Bloodroot [Sanguinaria canadensis] Beebalms [Monarda species], and Common Milkweed [Asclepias syriaca]), so for a thriving, pollinator-friendly yard next season, it is crucial to plan ahead and plant now. Check out the Wild Seed Project in Maine for native plant seeds that you can still plant this autumn.
Second, as our colleagues at the Xerces Society for Invertebrate Conservation like to say—leave the leaves! Resist the urge to manicure the space around your home and leave those leaves where they lay. Leaf cover on the ground over the winter protects bare ground from erosion and desiccation. Leaf layers more than 2 inches deep can sometimes smother lawns, so consider raking the early leaf falls and leaving the later leaves where they fall. Pile the raked leaves atop your gardens and flowerbeds, and use the leaves as mulch around shrubs and trees. Insect eggs, larvae, and adults take shelter among the leaf litter, so resist the urge to shred the leaves. Just a sampling of the myriad of insects and life stages that overwinter in leaf litter include the eggs of Great Spangled Fritillaries (Speyeria cybele), the pupae of Luna Moths (Actias luna), the larvae of Baltimore Checkerspots (Euphydryas phaeton) and Isabella Tiger Moths (aka Wooly Bears, Pyrrharctia isabella), and bumble bee queens.
Third, leave rigid standing dead vegetation as homes for insects that overwinter as eggs, larva, and adults. For example, leafcutter bees (Megachile species) and some mason bees (Osmia species) overwinter as larvae in the hollow stems of plants around our homes. So instead of leveling your perennial wildflower garden flush with the ground in the fall, put the sheers away and leave your seed heads and perennial flower stalks intact over winter. The following spring, cut the stems at a variety of heights between one and two feet, bundle the cut pieces, and stash the bundles in your yard to provide even more habitat for spring-breeding insects. If you feel really strongly about tidying up the yard in the fall, and you’re compelled to cut back perennial wildflowers, then consider the intermediate approach of leaving one to two feet of rigid stems intact. Here in New England, many butterfly species overwinter as chrysalises on standing dead plants, including some of our swallowtails (Papilio species), sulphurs (Colias species), elfins (Callophrys species), and skippers (Hesperiidae)—another reason to leave rigid dead vegetation. Furthermore, by leaving seed heads, you will be providing a food source for birds and other winter wildlife.
Take this as an excuse to ditch the rake, spend the weekend on the trails instead, and rest easy knowing that your yard will be a winter safe haven for biodiversity.
For more insight, check out Nesting & Overwintering Habitat for Pollinators & Other Beneficial Insects by the Xerces Society, Doug Tallamy’s book Bringing Nature Home from Timber Press at your local bookstore, and Heather Holm’s YouTube talk on creating insect habitat around your home.