By Dave Shiley, Extension Educator-Local Food Systems and Small Farms

I am not sure where the summer went, and the fall is going by just as quickly. Cooler night temperatures should help bring out fall tree colors.  This week I wanted to pass along some answers to fall tree questions I have received in the past couple weeks.

The first question I wanted to talk about is “when to prune trees?”  Several residents have asked if they can start pruning their deciduous trees now.  The short answer is to prune deciduous trees in the winter, after they are dormant.  There are several reasons behind this recommendation.

In regards to oak trees, pruning during the active growing season can cause “bleeding” or release of sap from the fresh cut wound.  This can attract beetles to the wound.  The problem occurs when the beetle has previously fed on an oak tree with the disease called Oak Wilt, and feeding on your oak tree could transfer this disease to your tree.  If you have to prune an oak’s broken or damaged branch during the active growing season, apply a pruning wound sealer immediately after cutting the branch.  When pruning during the winter as recommended, do not use a pruning wound sealer.

When pruning other species of deciduous trees, such as maple, the recommended pruning time is winter during tree dormancy.  If deciduous trees are pruned in the fall, they may respond to the branch removal by sprouting new growth, especially when heavily pruned.  The can be a problem because this new growth may not have time to mature or “harden” before freezing temperatures arrive.  Freezing temperatures will kill this new growth and require additional pruning next year.

Another common tree care question has focused on watering newly planted trees.  If you planted a tree in the past two years, continue to provide supplemental watering to the tree when precipitation is less than one inch during a two-week period.  Tree roots will continue to grow this fall even after leaves have dropped, and until the soil is frozen.  Therefore, continue watering newly planted trees during dry periods through November.

Don’t forget to mulch newly planted trees too.  A recommended practice when planting a tree is to apply a layer of mulch over its root system.  This reduces evaporation of water from the soil making more available to the tree.  However, mulch applied incorrectly can potentially kill your newly planted tree. 

Never pile mulch against the tree’s trunk. Think about the shape of a bagel when applying mulch.  There should be very little mulch on the ground within two inches of the trunk and then taper it up to 2 to 4 inch depth.  Extend the mulch layer out to a width equal to the spread of the tree’s branches. 

Finally, it is not too late to plant a tree this fall, but get it into the ground in the next week or two.  Mulch and water the tree as previously described.  If you have other tree or horticulture questions, contact the University of Illinois Extension office in Champaign at 217-333-7672.  You can reach me at 217-543-3755 in Arthur.

For more information, contact Dave Shiley at 217-543-3755 or dshiley@illinois.edu