Rain was one clue. Cooler weather is another. It is now so late into autumn that it will be winter soon. Every regional climate experiences some degree of chill. Some, particularly to the north, experience frost. This limits gardening in two ways. Several species prefer a bit less cool weather. Several prefer a bit more. Every species prefers a particular range.

Apple trees, for example, require vernalization, which is a specific duration of chill. Some cultivars require more than others. Without it, they can not distinguish seasons, so do not know when to bloom for spring. Consequently, few cultivars of apple perform adequately within Los Angeles. However, many perform very well in the cooler climates of San Jose.

Banana trees, conversely, need no chill, and are instead set back by frost. Some tolerate a bit more chill than others; but ultimately, they are all tropical species. They produce fruit only within the months between frosts. Consequently, not many banana trees are notably productive within San Jose. However, they perform better in the climates of Los Angeles.

Banana trees stop growing when the weather is cooler than fifty degrees or so. That is a bit too much chill for them. However, frost does not occur until the weather is cooler than thirty-two degrees. Banana foliage can therefore be safely dormant during chilly weather. That is a range of twenty-two degrees. Different tropical species survive different ranges.

The simplest form of frost protection is to not cultivate species that are vulnerable to frost. This is, of course, a bit too restrictive for many who enjoy gardening. Instead, some grow vulnerable species in pots to move to shelter prior to frost. Some simply grow vulnerable species below the shelter of eaves or big trees. Tenting may also be effective protection.

Alternatively, some species can endure frost damage to recover during warmer weather. If possible, outer foliage that succumbs to frost should remain through winter. It insulates inner growth from subsequent damage. Besides, premature grooming can stimulate new growth that is more vulnerable. Many perennials prefer cutting back after winter anyway.