We were unable to water our rhododendron (4 feet high, purple flowers) for about 7 weeks, through some very hot weather. Now the leaves and flowers are mainly wilting, going brown and falling off. We've tried soaking it really well 3 or 4 times but it's made no difference. There's a tiny bit of sprouty new growth right on the top. What do I do? Cut back to very old wood? I don't want bare twigs with a few leaves at the top.