I learned last week (on this thread) that certain plants are poisoned by having a Walnut tree close by.
Do You have one?
http://gardening.about.com/od/gardenproblems/qt/Black_Walnuts.htm
Just an FYI
I’m going to have to replant my apple tree.
I wish I had a walnut tree. I’m in the Texas Hill Country. The only things that grow naturally here are juniper, live oak, mountain laurel, and cactus.