Answer: You can prune the aspen trees in late winter or early spring before they leaf out. If you prune them now they will ooze sap which can invite insect and disease problems. Wait until they are dormant and you'll avoid both these problems. Sealing wounds isn't recommended and won't actually stop the sap flow. Sealing can stop the natural healing of a pruning cut. So, wait until late winter or early spring, and don't dress the wounds. Good luck with your pruning project!
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