Evergreens are popular for home décor through winter because there is not much blooming so late in most other American climates. The tradition endures, even though cut flowers of all sorts can easily be purchased from common supermarkets nowadays. Here on the West Coast, where several varieties of flowers can bloom through winter, evergreen foliage is as popular as it ever was.
Christmas trees are the most substantial form of traditional seasonal evergreens. The biggest wreaths occupy less space, and are mostly confined to walls rather than floors. Garlands can be big too, but their less defined form fits more neatly into limited space. For many of us, neatness is not a priority. Displays of evergreens and all the associated ornamentation can get quite elaborate.
Not many of us grow our own Christmas trees. It is more practical to purchase them as if they are very large cut flowers. Most but not all of us who hang garland likewise procure it already made. Some purchase prefabricated wreathes too. However, it is possible that more of us create our own. Other bits and pieces of evergreens are unlikely purchased. Most are from our home gardens.
Most of the pine, spruce, fir, hemlock, yew, arborvitae, and various genera known collectively as cedar, that are traditional evergreens in other regions are scarce here. A few other exotic species of pine, as well as natives, are more common in some landscapes. There are also different cedar and arborvitae. Blue spruce can sometimes be found. Douglas fir is native to nearby mountains.
Other regions lack the abundance of various cypress and juniper that are common here, as well as coastal redwood. (Redwood foliage is perishable once cut.)
There are no rules about cut evergreens anyway. Within reason, we can cut and bring in whatever we happen to find to be appealing in our gardens. We should cut the foliage properly though, as if pruning. Also, we should not cut too much from any particular spot, but instead harvest evenly over a large area. It helps to take pieces that are out of view, or that need to be pruned out anyway.
English holly is politely naturalized here. This means that, although naturalized, it is not aggressively invasive, and does not seem to be too detrimental to the ecosystem. It is only annoying to see out in forests, far from the landscapes that the seed escaped from, and wonder if it has potential to significantly compete with native vegetation. It would be better if it were not there.

Autumn is not much to brag about here. It supposedly got just cool enough at night for the minimal requirement of frost, at 32 degrees, but no one noticed. It has been getting to the low 80s during the day. There has been no rain yet, and none is in the forecast. As bland as such weather seems, it is not at all out of the ordinary. Autumn often arrives later than it does elsewhere.
It is easy to mistake various cultivars of Dyckia for diminutive relatives of Agave or Yucca. They form stout rosettes of rigid leaves with wickedly sharp terminal spines. Their comparably nasty but incurved marginal teeth resemble those of most species of Agave, but are generally more abundant. Surprisingly though, Dyckia are instead related to bromeliads. They just happen to be xeric.
Some of us might remember Delta maidenhair fern, Adiantum raddianum, as a houseplant that was popular for terrariums in the 1970s and into the 1980s. Although quite happy in terrariums, it eventually gets big enough to crowd other plants in such tight spaces. It prefers to be potted on a porch, or in a regularly watered and sheltered spot in the garden. It tolerates quite a bit of shade.
Autumn foliar color is not the concern yet. It develops later as deciduous plants defoliate for winter. Purplish, reddish, yellowish, bluish or gray foliar color that can be seen now is provided by plants that are colorful while actively growing. Almost all of this sort of foliage is most colorful when it is young and fresh, early in spring. Then, through summer, some of the best foliar color fades.
Unlike the common bird of Paradise that is grown for striking bright orange flowers, the giant bird of Paradise, Strelitzia nicolai, is grown for strikingly lush foliage. The big rich green leaves get nearly six feet long, and flare outward from leaning trunks that can eventually reach upstairs eaves. Foliage is healthiest if sheltered from harsh sunlight (such as hot reflected glare), wind and frost.