|Pic taken from the AgriLife Extension in Texas|
"Iron deficiency, called iron chlorosis, can be seen on the leaves of apple, peach, and citrus trees, and on gardenia, hibiscus, pyracantha and rose plants. Although our desert soil contains plenty of iron, this nutrient is "locked up" in an insoluble form due to the soil's high alkalinity. As a result, non-native plants such as those mentioned above struggle to absorb iron. Native plants, on the other hand, seldom suffer iron chlorosis, as they have adapted to local soil conditions. Iron also is not available for absorption if the soil is cold or wet. The effects of iron chlorosis usually are visible in spring after months of cool temperatures, wet soil conditions, or during summer monsoon, when thundershowers are heavy. As these seasonal variations disappear, the problem typically clears on its own.