Continue grooming perennials, annuals, leaving some for winter interest
Continue to groom your perennials and annuals by removing yellowing foliage and spent flowers. Make note of perennials that have flopped and need staking so that a support system can be installed next spring before the plants actually need it. Gentle pruning back more vigorous perennials can help keep your border from looking overgrown. Cutting leaves off at the base can reduce the size of the plants without having them look pruned.
You may want to leave certain dried flowers on plants such as astilbe and coneflower for fall and winter interest. Goldfinches visit my coneflowers in the fall and eat the seeds.
Cicada-killer wasps are back
Cicada killer wasps have returned to my brick driveway right in front of the garage. They are making holes in the sand between the bricks in which they place annual cicadas paralyzed by a sting to lay their eggs on. These wasps will not bother you but do look intimidating. The males do not have stingers. There is no need to control them, and I am happy to see them back.
On alert for magnolia scale
This is the time of year to check for magnolia scale, an insect about the size of a pencil eraser. It’s typically found on the underside of magnolia branches; the scale is responsible for creating an overall thin condition on the tree. The scale exudes a clear, sticky honeydew after feeding on the plant. Black sooty mold is a fungus that grows on honeydew. Gardeners often notice the black mold on or under the magnolia before noticing the actual scale. This black mold on other types of trees can also indicate problems with other insects.
The mold itself is not the real problem. On small trees, simply pick off the scale and squash them. Other control measures include spraying with summer-weight oil, or applying an insecticide when the scale is in the active crawler stage, generally in early September. For trees with a history of magnolia scale, a late winter to early spring application of dormant oil will provide good control for the scale. If your tree is affected, provide extra water during summer to minimize stress. There is no need to use an annual spray program for magnolia scale — monitor your magnolia and treat as needed.
Flooded plants? How to manage
The Chicago Botanic Garden recently got more than 2 inches of rain. If your garden has flooded, give your plants some time to recover and remove any excess debris from the beds. The longer the plants were inundated with water, the more likely they would become damaged. Different types of plants will vary in their ability to withstand being flooded.
Hostas and daylilies that have been flooded at the Garden in past years did OK, while plantings of dahlias and salvia were quickly killed. Some shade trees may show early fall color as a stress response to being flooded.
If you’re unsure whether a perennial has died because of flooding, cut back the dead foliage and watch to see whether the plant pushes new growth over the next few weeks.
Any flooding damage to trees and shrubs will show up over the coming weeks. Any decision to remove plants will depend upon the extent of the damage, which is difficult to predict shortly after a storm. In most situations, it is not worth washing dried silt off the foliage of plants.
• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.