Question
I am having huge problems in my garden. This summer (and last) the majority of my plants drop their leaves after looking beautiful throughout the spring. It started again about a week ago just as it started to get warm. Leaves turn brown around the tips and edges, and they eventually fall off. The leaves normally fall off before the brown gets to the whole leaf. This is happening to my crape myrtles, asters, columbine, jasmine, potato bush and hibiscus. Some other plants are doing OK. I am good about watching how I water as the soil here in the Central Valley, California is clay based. Please help

Answer
Hi Margaret,

I have a feeling that what you are experiencing is a pH problem.  All of the plants you mention like moderately acid to neutral soil.  The soils of the central valley in California tend to be on the alkaline side.  When the pH is in the alkaline range (pH>8.0) certain nutrients become unavailable to the plants.  pH is also temperature related, so there may be a connection between the increase in temperatures to the increase in pH and the unavailability of nutrients.

If you have a pH meter, check the pH of the soil.  If you find that the pH is > 7.5, then add gypsum (calcium sulfate), agricultural sulfur buds (pellets) or a soil acidifier.  In addition, I would begin a feeding regime that provided additional micronutrients such as iron.  The lack of iron, in particular, causes yellowing of the leaves, and elemental iron is unavailable at the higher pHs.