Master Gardener: Helpful garden tips for December | Home and Garden

I’ve been thinking about plants of the late Pleistocene era, and the animals that ate them, described in a pictorial essay by David Bryant in the fall 2021 issue of Flora, the California Native Plant Society’s quarterly magazine. Among them are Joshua Trees, California lilac, manzanita, grasses, sedge, rush, Pinyon pine, juniper, and sycamore, to name a few. I’ve also been thinking about one of the biggest trends in gardening this year: “regenerative landscaping,” which is broadly defined as future-looking, considering all the creatures of the garden, recognizing that more than just humans use the space. As gardeners out in it, we know this mixed-use firsthand, but it can be valuable to take some time occasionally, such as in the slower winter months, to reflect, observe, appreciate, and plan. This doesn’t mean allowing total destruction by pest insects and herbivores. It means learning what is a tolerable threshold, using modern methods of IPM (Integrated Pest Management) and letting go of perfection.

Must we have an attitude of battle, or can we learn to share the garden, even making friends and allies with creatures beyond the hummingbird and butterfly? Can I learn to appreciate the Western ground squirrel?

While doing all this pondering, there are a few tasks we can do in December:

PLANTING:  Finish planting most species by mid-month. Bare-root planting begins in December and can extend through winter. Plants that are frost sensitive should not be planted until spring. Even for frost-hardy species, use a layer of mulch to protect plant crowns and roots from freezing. Finish planting bulbs for spring color. In the edible garden, in addition to perennial herbs, you can still transplant seedlings of most cool-season vegetables. Also plant bulb onions, asparagus, and rhubarb. These last two are perennials, so you won’t be harvesting them until well into next year. You can also plant lettuce and related salad green seeds in cold frames.

MAINTAINING: Watch for frost warnings and protect your sensitive plants. Plants will survive better if kept moist but not overwatered. Remove old fruits, called “mummies” left on fruit trees. Water citrus trees well this month if the rains aren’t steady to have a good crop next year. Also, deep water your other trees during a dry spell that lasts more than two weeks, even if they are dormant.

You can begin to prune your winter deciduous trees, shrubs, and fruit vines, or wait until January, especially if plants aren’t fully dormant and safety isn’t an issue. Don’t prune if frost is expected within the week. Force your roses into dormancy by removing leaves that haven’t fallen Mow cool weather lawns, which should be actively growing now, at three inches. This also applies to over-seeded lawns.

If you had major problems with aphids, mites, scale or whitefly on your fruit trees or roses, spray with dormant oil spray after the leaves have fallen to kill overwintering adults. Handpick slugs and snails or set out iron phosphate as a bait. You must replace iron phosphate after a rain, but it is not toxic to people, pets, and beneficial insects and won’t harm soil microorganisms either. In late December, spray early blooming peach and nectarine trees with copper fungicide to control peach leaf curl.

See any white moths around your winter veggies?  The moth is looking for good spots to lay her eggs, which will hatch into the cabbage looper and eat holes in the leaves, sometimes decimating the crop. You can’t do much about the moth, but seeing the moth is a signal to start looking under the leaves for the next several days to snag the small, green caterpillars before they do much damage. Large plants can survive some damage, but seedlings can be devoured. Chemical control is BT (Bacillus Thuringieis). Be sure to spray plant leaves thoroughly on the tops and bottoms.

Remember many caterpillars, especially on ornamental plants, do little harm and turn into desirable moths and butterflies. And all Lepidoptera are food for birds, lizards, toads, and other creatures in the food chain. Use common sense and a little tolerance for damage to encourage a healthy garden full of interesting life, even in the urban neighborhood.

Finally, keep up with cool season weeds so it doesn’t become a tiresome and overwhelming job later. Common household white vinegar or commercially formulated non-systemic organic herbicide can be kept in a labeled spray bottle in the garden to zap weeds on sunny days. Or lightly hoe them out. You can also try piling on more mulch and shading them out, which works well in these weak-sun days.

CONSERVING: Leave a pile of branches from trees and shrubs for birds to shelter in.

And don’t forget the water. Small creeks as part of a water garden design, mister-style sprinklers, or a bird bath with fresh water are all popular with our wild bird friends. When getting ready to prune trees, examine the high branches of large trees for bird nests and avoid pruning if hawks or other birds are nesting.

If you haven’t already done so, cut the flowers off tropical and other non-native, orange-flowered milkweed varieties. The Monarchs that stick around because of a ready food source will not survive the cold winter; they need to migrate south. You may want to consider replacing it with a native milkweed. On the other hand, we have so many hummingbirds that do not migrate, it is okay to continue to provide them with hummingbird feeder food through the winter.  

I hope you have wonderful winter holidays, full of beneficial garden companions and delightful surprises.

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