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December: Compost leaves, tidy your tools, then enjoy the holiday
Fall is officially over in December, but the planting season continues right into January. Because soils have cooled and growth everywhere in the garden is at a near standstill, new plants will not become established as quickly as they would if planted in late October or early November. But it's still a better time than spring or summer to plant many things. Even in warm, dry autumns such as this one, the shorter days, low sun and cool nights make for a less stressful start on life. With any luck more rains will come and help out with the watering.
Leaves finally color and fall in most of the L.A. Basin. Trees may be bare already in the mountains and in some inland areas. Though we are not famous for our autumn foliage, the colors are quite good inland where the nighttime temperatures are the nippiest, though some trees color well even near the coast, including the ginkgo, with its prehistoric triangular leaves of blazing gold, and liquidambar of various colors.
Where nights are colder — in the San Fernando and San Gabriel valleys for instance — you'll see decent reds and oranges on sour gums and Chinese tallow trees, as well as the bright, clear yellows and gold of Modesto ash, poplar and zelkova. Chinese pistache is one tree that seems on fire it becomes so colorful. If you shop for these trees while they are in color at nurseries, you will be sure of what you are planting because colors can vary dramatically from tree to tree. Several others to look for include Japanese maple, locust, Chinese flame tree (Koelreuteria), crape myrtle, persimmon and sassafras.
If you're wondering why anyone would plant a deciduous tree when there are so many others that never lose their leaves, a deciduous shades house roofs or patios in summer but lets the warm sun through in winter. Leaves fall all at once so the raking is over within a short time, unlike evergreens, which shed for months. And some gardeners just like reminders that we do have seasons in Southern California.
Start a pile
When leaves do fall, make sure you put them in a compost pile, a valuable garden commodity. Weeds don't make good compost because they may have seeds; garden prunings may take a year or more to decompose. But autumn's softer leaves decompose by spring, helped by winter's dampness, which speeds the process. Homemade compost works as a soil amendment and a mild fertilizer, making soils much more manageable and productive. Make a simple pile from a circle of wire fencing (at least 3 feet across), and dampen the leaves as you fill it.
Garden tools never get a break in California, but the last few weeks of December are the closest they'll get. Use this time as an opportunity to care for them. First scrape dried dirt from the blades of spades, shovels, forks, trowels, rakes and hoes. In other parts of the country the metal parts are often coated with heavy oil to protect them from moisture, but there's no need to do that here. It's the wooden handles that need protection from drying out. Wipe or brush plain linseed oil on the wood and let it sit overnight, wiping any excess the next day. Doing this once a year makes the handles last nearly forever. (This gardener has a spade more than 40 years old that's still in constant use.) It also prevents splitting and splinters. Wear latex or vinyl gloves when applying the linseed oil because it soaks into hands as well as wood.
Things to plant
The best time to plant natives and other plants from Mediterranean climates is during our cool season. Most plants from temperate climates, such as camellias, also do best planted now. Only subtropical and tropical plants are best planted in spring because they do their growing when the weather is warm. The best selection of roses and deciduous fruit trees arrive at nurseries late in December.
There are all sorts of bedding plants to put in now, such as Iceland poppies and pansies. Though seeds may be slow to sprout in December, many vegetables, including broccoli and lettuce, prefer the cool season. And don't forget to plant any bulbs that have been cooling in the fridge.
It's best to look for poinsettias not sold in their paper or plastic packing cones because the plants are less likely to drop bracts ("flowers") and leaves. Living Christmas trees will shed needles if they stay indoors for more than two weeks. Remember to keep saucers of some kind under all pots and to water. When you do move trees outside let them reacclimatize by first keeping them in bright shade. Consider keeping them in pots because most become really big trees in the ground.