Q. Will it hurt evergreen trees to put woodchips around them as mulch if the chips are from recently chipped up trees and branches (green)? Bob Heacock – Harleysville, PA
A. Over the years there has been some controversy over using fresh wood chips as you describe in the landscape. The issues of soil nitrogen depletion from the mulch, disease transmission from the source material, oxygen depletion have all been raised when using fresh (not composted or aged) mulch. Most current though in the agricultural extensions and colleges indicates that nitrogen depletion from fresh mulch only affects the surface of the soil where at the mulch/soil interface. This means that established plants that have extensive root systems below the soil surface will not be affected. Disease transmission is rare, especially if you use hardwood mulch (from deciduous trees) on evergreen trees, as is in your case. If you know the source of the recently chipped trees and branches to be disease free then the chance of this being an issue is remote. The thickness of the mulch would need to be quite deep to prevent gas exchange between the soil and the atmosphere above. If you are mulching within normal ranges of 2-4 inches this will not be an issue. So I would say that your evergreens would benefit from the fresh mulch.