Answer: Newly planted trees benefit from a minimum of root competition, so planting anything right around them is probably not a good idea for the first few years. Vines in particular can cause problems because they are heavy and can act like a sail in windy conditions causing extra stress on a young trunk and newly establishing root system; they also compete with the tree canopy for light and air. In your case, the Kwansan was apparently large enough to withstand the competition, but a smaller or less vigorous type of tree might not have been. Even though it is late in the season I would probably remove the vines because they will continue growing vigorously until frost; the tree will also continue pulling water and storing nutrients throughout the fall and will need all the resources it can get to come out of winter and go into spring in the best condition possible.
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