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Over the Garden Fence

Spring FAQs from the Master Gardener Help Desks

Our Master Gardener Help Desks are now open for the season, and visits, phone calls, and emails have started out strong. Here are some of the highlights in the last couple of weeks:

Weather related to landscape plants

Q:        Is it too late to prune oaks to help prevent the possible spread of oak wilt?

A:        Best range is November through February. This keeps us clear of oak wilt season. As of this column, we are really too close to sap flow to risk it.

Q:        What are the guidelines for applying dormant oil sprays to my apples?

A:        Dormant oils should be applied to the point of run-off when there will be temperatures that remain above freezing for 24 hours or more. The oils work by smothering overwintering adults and insect eggs found in cracks and crevices of the bark and exposed on twigs and branches.

Q:        So, what is the difference between renovation pruning and renewal pruning on my landscape plants?

A:        In short, “renovation” is the removal of all branches as near to the soil line as possible to allow for all new growth to emerge from the crown. Often done to recover shrubs that have become totally overgrown. “Renewal” pruning allows a homeowner to recover a somewhat overgrown shrub over a period of three to four growing seasons. The goal is to remove a percentage of the older growth down to the crown or very close. Older wood can be diseased and harbor insects, and it is normally the taller growth. By systematically removing older growth over time, the plant will be reduced in overall size, have a better shape, and if a blooming shrub, provide a better show of flowers. Both types of pruning should be done right now before sap flow begins up into the stems.

Weather-related issues of insects of all kinds

Q:        Why have we started seeing ants and boxelder bugs inside already?

A:        Insects, and insect relatives like spiders, have begun to come out of winter hibernation. The warmer their surroundings, the sooner they show up. Any insect that took cover on a southern or western exposure will be the first ones out and about. Once the home wall warms to a consistent temperature, the insects will become mobile again, and begin to show up just like they did last fall until cold weather stopped movement. Inside they are just a nuisance as they cannot survive without a food source. Outdoors their activity is a lot slower having to deal with the changing daytime and nighttime temperatures. They will disperse into the yard as they are able to for the rest of the summer.

Squirrels, voles, field mice, and rabbits

Q:        We’re seeing [insert critter here]. Are they damaging our plants?

A:        Rabbits have been feeding somewhere all winter long and will be expanding their territory as weather warms. Before the grasses and weeds green up, dinner will be our perennials, thin-barked trees and shrubs, etc. Field mice damage is most often found at the base of shrubs and the surface of roots. Vole damage in the lawn goes away as the bird feeder gets put away and normally does not require repair. Ground squirrels are not the same and be seen all summer long. Squirrels will be digging in beds and the lawn looking for their buried treasure from last fall.

About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.