We planted ground cover ceanothus in gallon cans in March of 2012. They all established and started to grow and put out new growth. Now one by one they are dying. First some of the branches turn brown and then is seems to spread. They are not on drip irrigation. The soil is clayish, and I always expect to lose a few plants but it seems to be spreading. We had the best luck with the plants on a hill, but those are staring to go as well. What concerns me most is that after one plant dies, the one next it is does. It does not appear ran dom. Help!