Answer: You didn't describe where they are in the garden, how much sunshine they're getting, how much water, etc. so I can only guess. If the edges of the leaves are turning crispy brown, the most common causes are too much sunlight or too much/too little water. Japanese maples cannot tolerate hot afternoon sunshine but they love growing in dappled shade. If you haven't yet planted them, move them to a more protected spot. If you have planted them, you might want to provide some temporary protection from afternoon sunshine and then plan on moving them this winter when they are dormant.
Best wishes with your new maples!
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