Make sure that you are keeping them well watered.

Also make sure that you didn’t plant them too deep.  Get under them and brush away any mulch and soil away from the trunk several inches until you find the original soil that the plant came with and keep it that way. Soil or mulch piled against the bark stops the flow of moisture and nutrients from flowing through the bark from the roots below to the foliage above.  It like slowly strangling them.

You could also give them a boost by soaking the soil with a good soluable food like Jack’s All Purpoase Plant Food 20-20-20.