When plants begin browning soon after planting it is a good idea to check the moisture in the root balls of the plants. Sticking a finger into the root ball in a few places with give you a good idea of how wet or dry it is. How often have you been watering the plants? A typical watering schedule for newly installed plants would be to water daily for the first two weeks, every other day for two months, then weekly until established.

It is very important when watering newly installed plants to make sure that water is directed to the root balls of the plants, not just to the surrounding soil, since water will not move laterally from the surrounding sandy soil back into the more organic soil of the root balls. Hot, dry conditions like we have been experiencing recently make this especially important.

See this website for more information:

http://hort.ifas.ufl.edu/woody/irrigation2.shtml