October may bring cool or warm days, sun or clouds, and our first frost of the season. The last few flowers on New England asters (Symphyotrichum novae-angliae) and showy goldenrod (Solidago speciosa) signal the end of the blooming season. A few pollinators (mostly male bumblebees, some wasps, and a few butterflies) are still active early in the month, but not at the end. Several common animal species (chipmunks, woodchucks) go into hibernation in October. Bird activity and migration is marked by feeding on grass and forb seeds and the arrival of dark-eyed juncos, a “winter” species for our area. Fruit and seed dispersal by animals and wind continues for late-blooming plant species. Native garden tasks include trimming edges of garden beds (to prepare for snow removal), seed harvesting, weeding, removing seeds before dispersal on native plants that have proven highly aggressive in the garden (e.g., pale Indian plantain, Arnoglossum atriplicifolium) or that grow where they are not intended (“right plant, wrong place”).
How to winterize a native plant garden? At the Arboretum, we leave most of the plant material in place throughout the winter. Fruits and seeds provide for plant reproduction and support local wildlife with food. Plant stems and leaves may harbor or protect overwintering insects. Plant material provides cover for wildlife, which in turn supports predators like coyotes and birds of prey. Soil is covered and protected from erosion and drying. In the Arboretum native plant garden, the remaining plant material helps define the paths and trails, which prevents trampling and damage when the garden is blanketed with snow. In late winter, we use prescribed fire in some areas and trim others to make way for new growth. In the meantime, we enjoy seeing plant structure, branching, colors, and patterns as early winter approaches.
I am grateful for strong interest in last month’s column on container gardening with native plants, and for your feedback. Some readers asked for advice on how to care for containers during winter. One of our experts leaves the plants in place in large containers over the winter, and he especially enjoys the native grasses backlit by low-angle afternoon sunlight. In late March or early April, he clips the dried stalks to six inches and removes the coarse material. Some clippings can be left on the soil. He may add some light organic compost in April, but no chemical fertilizers. If needed, it is best to add soil during the growing season, to prevent damage to the crown and new buds of the plant under the soil surface. Our other expert sometimes moves her containers next to her building before snow, but not always. She reports that they survive most of the time, even during severe cold like we experienced in 2019.
In summer 2020, two monarch and milkweed experts tried growing swamp milkweed (Asclepias incarnata, two-year-old plants) in large pots. The plants thrived, grew to full size, bloomed profusely, and set good seed, despite the hot and dry weather in August, even though this species grows best in moist soils and wetlands. Monarchs and pollinators made many visits to the container plants. The gardeners watered the plants regularly, but not as often as they thought would be needed. They will monitor those containers to see if the plants survive the winter. These are great examples of how simple experimentation and monitoring can help you understand your site and learn more about the plants. Sharing what you learn benefits everyone. Enjoy fall and its many transitions in your garden!
—Susan Carpenter, native plant gardener