Answer: Japanese maples prefer filtered sun or shade most of the day. If you can find a spot that provides a bit more shade, the leaves will be less prone to sunscald. Brown, wrinkled leaves can indicate sunscald and/or fertilizer burn. Plants in containers are quite susceptible to fertilizer build-up, even from slow release granules. Too much water can cause problems which show up on the leaves, as well. Here's what I would do: move the tree to a location that is shaded from sun from at least noon on; water thoroughly, then allow the top inch or two of soil to dry out before watering thoroughly again (you can count the number of days this takes and then reset your sprinkler system so that it waters only that often). Instead of using time-release fertilizer, feed your maple with a water-soluable fertilizer, diluted half-strength and applied every 2-3 weeks during the growing season. Feeding in this way provides an almost constant source of nutrients to the roots of your plant.
Hope this information helps!
Q&A Library Searching Tips