Helpful Garden Tips for December
By Peyton Ellas
12:56 pm,
November 30, 2023

December is the coldest month of the year in our area, and the winter solstice occurs this year on Wednesday, Dec. 21 at 7:27 p.m. It’s the shortest day of the year, the first day of winter, and from then on the days will be getting longer. Celebrations around the solstice are most often marked with greenery for the promise of a returning spring, yule logs and candles to increase the light for the day, and in general everything nature-related to remind ourselves we live on a living, changing, complicated planet in a vast universe. What better companions to pondering these deep thoughts than applying our muscles and energy to a few winter garden tasks? If you’re not up for working, at least try to get out in the garden a little that day. If it’s raining and you can’t track the sun, plant some wildflower seeds, as a rainy day is perfect for that task. 

Planting: Bare-root planting begins in December for roses, berries, and deciduous trees. Plants that are frost sensitive should not be planted until spring. Even for frost-hardy species, use a thick layer of mulch to protect plant crowns and roots from freezing. Finish planting bulbs and wildflower seeds. 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. Did any of you notice in increase in fruit quantity on your citrus trees this year? Most likely that is due to the abundant rain last season. Deep water your other trees during a dry spell that lasts more than two weeks, even if the trees are dormant. It’s always good to remember that our plants have a timeline much slower than ours, and actions taken now (or not taken) may not show up until next spring or summer. 

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 high. 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 horticultural oil spray after the leaves have fallen to kill overwintering adults. Handpick slugs and snails or set out iron phosphate as bait. You must replace iron phosphate after a rain, but it is not toxic to people, pets, and beneficial insects, and doesn’t appear to harm soil microorganisms either. In late December, spray early blooming peach and nectarine trees with copper fungicide to control peach leaf curl if you’ve had symptoms this year.

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 lopper 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. I’ve been hand picking for a month already on my bok choy and broccoli seedlings. Chemical control is BT (Bacillus Thuringieis), commonly sold under trade names such as “Caterpillar Killer.”

Finally, keep up with cool season weeds so it doesn’t become a tiresome and overwhelming job later. A commercially formulated nonsystemic organic herbicide can be kept in a labeled spray bottle in the garden to zap weeds on sunny days. Or hand-pick 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. Hay and straw make good mulch in the edible garden, but won’t shade out all the weeds, so be ready to hand remove as needed. 

Conserving: 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. 

Leave a pile of branches from trees and shrubs for birds to shelter in if you can. 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. 

If you haven’t already done so, cut the flowers off tropical and other nonnative, 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. Better yet, replace your nonnative milkweed with a California native variety. 

Cover bare soil with plants, mulch or erosion control fabrics to reduce losing more of your topsoil. If you have significant storm water runoff, consider installing a creek, rain basin, swale or French drain system. 

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

This column is not a news article but the advice of the writer and does not reflect the views of Mid Valley Times newspaper.

About the Author

Peyton Ellas
Peyton Ellas is a UCCE Master Gardener and is owner of Quercus Landscape Services and Auntie’s Home Grown Farm in Springville.