UNITED STATES—Indian summer is more typical here than not. As usual, the weather cooled somewhat as summer finished, and then warmed again. It is now autumn by date, but still seems to be summer by weather. This might confuse some vegetation, although some is familiar with this pattern. Some vegetation reacts by shedding foliage prematurely, prior to dormancy.
Prematurely shedding foliage is not the same as defoliation of deciduous species. Many of the species that exhibit such response to the weather are evergreen. More importantly, both evergreen and deciduous species do it prior to autumn dormancy. Also, they do not defoliate completely. There will be enough deciduous foliage for autumn foliar color later.
In the wild, prematurely shedding foliage is common among native California sycamore. It is a natural response to minor desiccation from any combination of aridity and warmth. It is as random as weather. Anthracnose is a foliar disease that might cause more severe defoliation earlier. Either type of shedding may be visually unappealing, but is harmless.
Premature shedding is a defense mechanism.
Actually, premature shedding foliage is common among many regionally native species. It helps them survive within chaparral climates. Although not a problem in the wild, it can be messy in or adjacent to refined landscapes. Both coastal redwood and coast live oak are notoriously messy. Yet, both species are evergreen and endemic to coastal climates.
Some exotic species from various climates can exhibit prematurely shedding foliage too. Species from other chaparral or desert climates are naturally proficient with the process. Species from less arid climates learn fast. It can be stressful for some of them. Daylength assures them that shedding is now safe. However, warmth that necessitates it might not.
Various species react variously to the various causes of premature shedding. That is too many variables. Simply, shedding is different every year because the weather is different every year. Eastern redbud and birchs that are exceptionally messy now may not be next year. Japanese maples happen to be shedding a bit less this year than they typically do.
Highlight: Coastal Redwood
Not every garden can accommodate coastal redwood, Sequoia sempervirens. Wild trees can grow hundreds of feet tall, with trunks as wide as thirty feet! None are so big in home gardens, but only because they are still young. They can live for more than two thousand years. By that time, those in urban landscapes are very likely to become major concerns.
Realistically though, urban trees are generally more compact than wild trees. There is no need for extreme height without competition from other similarly tall trees. Besides, lower trees are less vulnerable to wind. Warm and dry wind can desiccate foliage. Strong wind can dislodge branches. Limbs that fall from very high canopies are extremely hazardous.
Almost all modern coastal redwoods from nurseries are of the cultivar ‘Soquel’. They are strictly conical and symmetrical in form, with uniform foliation. ‘Aptos Blue’ exhibits more relaxed form and very slightly bluish foliage. ‘Santa Cruz’ should be more available than it is since it is more resilient to arid warmth. Old seed grow trees are genetically variable. For old formal gardens, they are less formal than younger trees.
