Ask a Master Gardener About Trees

March 20, 2019

Questions from University of Illinois Extension, DeKalb County Horticulture Help Desk


When winter finally ends we are eager to get out there and begin our planting projects. Mosquitoes, heat and humidity are a distant memory. We are excited about the new season and know it will be better than ever.

Some of the most common early-season questions we get at the Horticulture Help Desk are about trees.

Q: If I remove a dead tree and have the stump removed can I plant another tree in the same spot?

A: It’s not recommended. Instead, plant the new tree at least three feet away from the old location. The mushrooms will love you.

Q: What type of tree should I plant to replace an ash tree that was destroyed by Emerald Ash Borer?

A: Unfortunately, it is difficult to recommend a tree without knowing where it will be planted. For help selecting the best tree for your situation see:

Start by looking at “About this Site.” It will help you make an informed decision about the best tree for your landscape.

It is estimated that tens of millions of ash trees have been killed throughout North America. People with woodlots wish there was an Emerald Buckthorn Borer instead.

Q: What makes holes in tree bark?

A: If the holes occur in straight lines, the damage is probably from Yellow-bellied sapsuckers during their spring and fall migrations. Extension says they can be scared off if you tie an inflatable snake in the tree during migration. Or, wrap previously damaged areas with burlap or other protective material, but do not leave it on during the summer. They favor pine, spruce, birch, sweet gum and fruit trees. It is unlawful to harm this bird. Somebody should tell the cat.

Insects that feed inside trees during their larval stage leave exit holes. Some insects feed deep within trees.  The Emerald Ash Borer tunnels just beneath the bark. Knowing the type of tree can narrow down the source of the holes.

Q: What kinds of evergreens are suitable for this area?

A: For a list of  the “Best Evergreens for Northern Illinois” –  pine, spruce, fir and broadleaf evergreens, see the website below. Spoiler Alert: Colorado Blue Spruce did not make the list.

Q: When is the best time to prune the trees in my yard?

A: Light pruning can be performed on most deciduous trees at any time. Heavier pruning is best done in late winter when it’s easier to see the structure of the tree, before new growth begins. Leave the climbing to a professional.

Oak trees should only be pruned in the winter months when they are dormant, to prevent the spread of the fungal disease, oak wilt. Maple trees bleed sap and should be pruned while the trees are dormant. Research has shown that tree wound paint has no benefit. If pruned correctly, the wound’s edges will begin to callus.

Q: The tops of some of my trees have started to die out over the last few years. What causes this?

A: There are many reasons for a tree’s decline. A local certified arborist should be called in for an on-site evaluation, especially if symptoms persist into the next growing season. For names of local arborists call the Extension Horticulture Help Desk at 815-758-8194.

Q: When should I plant a tree?

A: Spring is the best season to plant seedling-sized trees and also nursery trees that were container grown or balled and burlap. Over the summer growing season they will have time to develop a strong root system. See Extension Educator David Shiley’s website for tips on the planting and care of new trees:

Janice M. Weber – University of Illinois Extension, DeKalb County Master Gardener