Question
I purchase a weeping cherry this past spring and planted it, all has been great.  However, in the past several weeks the leaves are turning yellow.  I'm in southern California and our weather has been extremely hot, but nothing else has changed.  It's on a slight hill so has great drainage and good mulch of about 2"" around it.  Doubt it's lack of water and I can't imagine in this heat that's it's too much water.  Please help.

Answer
A tree needs about 1 inch of water per week. Most sprinkler systems for lawns produce a lot less than this and the grass will get most of the water. The extreme heat will require more water. I would place a pan under the tree and turn the sprinkler on and when the pan has 1 inch of water in it stop. Do this every fourth day until it rains and the weather gets a little cooler. Fertilize the tree with 10-10-10  fertilizer at the rate of 1 lb of fertilizer per inch of trunk diameter scattered around the tree and watered in good.