Evergreen plants retain foliage throughout the year. Deciduous plants defoliate for part of the year. That is the simplest explanation. The various reasons for shedding or retaining foliage are not so simple. Annual plants die after their single growing seasons. They can not live long enough to be either evergreen or deciduous. Some plants just may be both.
Foliar color, to some extent, conforms to preferable environments. Monterey cypress and Monterey pine have richly deep green foliage. It maximizes absorption of sunlight within the foggy coastal regions that the trees inhabit. Blue spruce has glaucous bluish foliage. It reflects a bit of sunlight to protect from sun scald within severe high mountain climates.
Similarly, deciduous plants generally defoliate for environmental situations. Most go bare for winter, in order to be less susceptible to damage from wind and snow. Bare stems do not collect as much heavy snow as foliated growth. They are also less resistant to wintry winds. If foliated, they are more likely to succumb to wind or overburdening snow weight.
Evergreen plants may retain their foliage because they are from climates in which winter weather is not so harsh. Wind may be no more extreme than it is in other seasons. Snow may never occur. Plants from tropical regions may be unfamiliar with colder weather and shorter daylength associated with winter. Their evergreen foliage might function all year.
Some tropical plants that are evergreen within their native environments may defoliate or die back as a result of even mild frost. Some recover as if deciduous. (Those that can not survive local climate conditions are not very popular here.) For example, canna die back to the ground after frost, but regenerate later. In tropical climates, they can be evergreen.
Evergreen species from mountainous regions or extreme northern latitudes are generally uncommon here. They prefer harsher weather. Although evergreen, they are remarkably resilient to wind and snow in the wild. They are likely evergreen to always stay receptive to limited sunlight whenever it is available, though wintry weather is possible at any time.
By ‘big trees’, I don’t mean the various ficus trees that can grow up to the ceiling, and be quite happy inside. I am referring to the shade trees that live out in the yard, or forest trees that live beyond that. They are outside for a reason . . . or actually, several reasons. They are too big to bring inside. They probably would not like the climate inside. No one wants to rake fallen autumn leaves inside. Well, you get the point.
Fire has always been a part of life in most of California. That is why almost all native flora benefits from it, and has developed an efficient system and schedule for not only living with it, but exploiting it.
Junipers have a bad name. So do eucalypti. Too many of the wrong types were planted back at a time when they were too trendy. Those that were planted into inappropriate situations grew up to cause problems. The names of all junipers and eucalypti are now synonymous with those problems, even though there are many types of both genera that are quite practical for landscape purposes.
Is it coming or going? Autumn that is. It normally gets here last. We are typically only beginning to see the first foliar color of autumn while other parts of America get their first snow. We typically get a few more tomatoes out of our vegetable gardens long after most everyone else has pulled out their frosted tomato plants.
