Days and nights are turning cooler, some trees are beginning to show autumn leaf color, and the growing season is drawing toward its end. But that doesn’t mean a gardener’s work is done.
“There’s still plenty to do,” said Sharon Yiesla, plant knowledge specialist at The Morton Arboretum in Lisle. Here are some outdoor tasks to consider for autumn.
Keep watering. “Plants are still in business, and that means they need a water supply,” Yiesla said. Perennials, trees and shrubs grow new roots in fall, even after they stop blooming or drop their leaves, so they need moisture in the soil.
Evergreens, in particular, need fall watering to protect them in winter. Unlike deciduous trees and
shrubs, they keep their leaves all year and don’t become completely dormant. “They need to be fully stocked with water to resist damage from drying winter cold and winds,” she said.
This September has been a dry month in Illinois, with little rainfall, so watering is especially important.
“Anything you planted this year is especially vulnerable,” Yiesla said. “Those new trees and perennials don’t have a lot of roots, and they really need water to develop their root systems. Trees also have their best fall color if they are well-watered.”
Assess your garden. While you can still see the foliage of garden plants and remember their blooms, consider what worked and what didn’t. Look for opportunities to improve the garden next year — perhaps by adding more late-blooming plants to support pollinators in summer and fall, or plants to fill in empty spaces or screen an unwelcome view. Make notes about what you would like to try out or do differently next year.
Plan for dividing and transplanting. Look for plants that have overgrown their space and need to be either moved or tamed by dividing. “In fall, you can divide spring-blooming perennials or summer plants that are past their bloom,” she said. “If a plant is still in flower, mark it so you’ll remember to divide it in spring.” Fall is also a good time to transplant most shrubs.
Prepare for winter pruning. It’s best to wait until winter to prune. Pruning in autumn would stimulate new growth at a time when plants are trying to slow down. But fall is a good time to make a note of shrubs that will need attention in the winter dormant pruning season.
Abandon annuals. Colorful container flowers and vegetable plants that are past harvest can go in the compost bin.
Cut some perennials back. “Remove anything that had disease or pest issues and dispose of it in the landscape waste,” Yiesla said. “You don’t need to remove all flower stalks. Leave some for winter interest.” Perennials such as echinacea not only have striking shapes in winter snow, but their seeds are feeding birds.
Get ready for frosts. Have old sheets, a light tarp, or plenty of fallen leaves handy to cover plants if an early frost threatens. “Our weather is becoming more changeable and less predictable,” she said. “It’s important to watch the forecast and be ready.”
Plant bulbs. Get daffodils, tulips, crocuses and other spring-flowering bulbs into the ground from late September through October. “While the soil is still relatively warm, they will be growing roots,” Yiesla said. “As the soil grows cold, they’ll will go dormant and wait to bloom in spring.”
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424,
mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.