It seems that only a while ago, we were hoping that the warm weather would end. Now, summer seems to have been too mild for too long; until the recent warming weather. Tomato plants that were actually scalded when there were still young by the early heat in May, have been less productive than they should have been by this time of year.

The most difficult environmental condition to modify is the weather. All the soil amendments, fertilizers, and irrigation will not compensate for it. All one can do is wait for better weather. As things warm up, most plant species can continue production as if nothing out of the ordinary has happened.

Unfortunately, not all species respond to the unusual weather the same way. Some may exhibit symptoms that are perfectly normal for the species, but may cause concern for garden enthusiasts who witness them.

For example, the summer dormancy of blue oaks that I’ve described in the past may be observed among some of the more exposed individuals. Summer dormancy occurs when an individual is unable to preserve its own foliage during exceptionally warm, dry periods. Instead, the foliage is abscised before any more resources are expended. New foliage is produced when the weather is more conducive and abscised as normal in autumn.

This procedure is common among many of the California native species. Those in irrigated landscapes may respond similarly to those in the wild as a result of temperature and humidity. Many species that are not native, but endemic to similar climates have developed similar defense mechanisms.

Of course, not all species that respond in this manner defoliate completely. In fact, many drop only a few of the older leaves. For many species, abscised foliage may remain attached, but discolored.

Examples of herbaceous plant species that behave in this manner (usually with inadequate irrigation) include many vegetable plants, such as tomato, pepper, potato and eggplant. Tree species that may drop foliage include California buckeye, blue oak, California sycamore as well as the non native fig trees.

The symptoms are harmless to the species involved and require no corrective procedures. One can only wait for the weather to change.