We planted 3 five foot crepe myrtles about four months ago. They all leafed as soon as it got warm but all the leaf tips are brown and crisp. We always have either a cold or hot wind blowing. Also, our soil is very alkaline. We live in central Tx. What can I do to make them grow and turn green? We also have six other myrtles that are about eight feet tall that were here before that are doing fine.