Answer: If the branches are gray, there's not much hope for your champaca. These trees need perfect drainage (which I'm sure your slope provides), but they also need deep watering - something your sprinklers may not be providing. The planting hole should be deeper and wider than the rootmass and the planting area should be improved with organic amendments to help hold moisture deep beneath the soil surface, where the roots are. After your sprinkler runs on a regular schedule, dig down into the soil to see how deeply the moisture penetrates. You may be surprised at how shallow the moisture remains. If you decide to replant, be sure to amend the soil with compost, aged-manure, etc., and then plan to hand water your trees until the roots become established. After the first year, the roots should be established enough that you'll only have to water deeply once each week. Building a watering basin beneath each tree might help; you can flood the basin, allow it to drain, then flood a second time. This method of watering will concentrate the water over the rootmass and allow it to slowly trickle down, wetting the entire root mass.
Best wishes with your landscape!
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