Answer: Fall is really the best time to transplant your maples. If you're going to keep them in containers, you can use any good potting soil or even a 50-50 mixture of garden soil and potting soil. The leaves of Japanese maples can develop crispy margins if they are exposed to hot afternoon sunshine or if they receive too much nitrogen fertilizer (which shows up as scorched leaves). It sounds as though your trees are getting mostly shade, but you might want to watch and see just how much direct sunlight they are actually receiving. The leaves are also susceptible to wind burn. Maples like moist but not overly wet soils. I feed mine with a half-strength dilution of liquid fertilizer every 2-3 weeks during the growing season. This method provides a constant souce of nutrients without the possiblility of overfertilization. You might try this method to avoid root burn.
Hope this information helps you determine just what is causing the leaf scorch in your maples so you can avoid the same problems next summer.
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