December gardening tips and a few gift ideas for the green thumbs on your holiday list

The holiday season is a great time to garden and to indulge the gardeners you know. Looking for a garden gift? My favorite gifts to give and get include:

Uncommon plants
A sturdy trowel
Pruning shears that fit the hand perfectly
A weather station to monitor rainfall and temperature
Sturdy, soft gloves
A sharp weeding scythe
Hand lotion
A worm compost system — with worms, of course!

Irrigation

Even though the weather is dry, the sun is low in the sky, so plants need water much less often than in the summer.

How long to water? Run your irrigation system one zone at a time. As each zone finishes, stick your finger all the way down into the soil, as deep as you can. Is it wet all the way down? If not, run the irrigation again. Figure out how long it takes for the water to reach the roots. That’s how you figure out the run time for each zone.

Are you watering often enough? Too often? Do the canary test to figure out how often to run each zone. As you run each zone, mark the date on your calendar. Then turn the zone off. Watch that area of your garden for the first plant to have droopy leaves (that’s the canary) and check your calendar. Run the water just short of the time it took for the first plant to droop. Use this information to set how often each irrigation zone runs. Don’t expect them all to be the same. So, if it took 12 days for the first plant to droop, run that zone every 11 days. If it drooped after three weeks, run the zone every 20 days. Where the first plant drooped after a week, run that zone every six days, and so on.

Be sure to run your irrigation the day before Santa Ana winds are expected. Saturating the soil protects plants from desiccation.

If you still use overhead spray, it is time to switch to inline drip. Inline drip — basically long flexible tubing with emitters embedded inside the lines — is the most efficient and effective irrigation available.

Manage water

Water cisterns allow you to capture a large volume of water and use it over time. Some cisterns are installed above ground, others are buried underground and out of sight. These systems are made of sturdy materials such as concrete, fiberglass and polyethylene.

Water cisterns can hold hundreds to thousands of gallons. Choose a size based on the size of your roof. From an inch of rainfall, the typical yield is 62 gallons of water from every 100 square feet of roof. Direct the downspouts from the roof to the cistern.

As you prepare planting beds, shape the soil to include dips and swales to capture water so it can percolate into the surrounding soil. Bank water now to make it available for long-term withdrawal by plants’ roots in the spring.

If you have a spot that floods regularly, reconfigure the contours, install a French drain, lay out sandbags, etc.

Empty water that accumulates in dishes under potted plants, buckets, containers and other places where the constant moisture can drown plant roots or become a mosquito nursery.

Clean rain gutters. When clogged rain gutters overflow, the falling water destroys in-ground plants below. Compost the debris or use it as mulch.

After the rain, stay off the soil for two days. Wet soil compacts easily, so rather than dig or weed or plant, do chores such as repotting plants, cleaning your toolshed and planning for spring.

Update ornamentals

One of the most important ways to manage water is by carefully choosing and managing your plants. This is the time to plan and implement a drought-tolerant strategy.

Look for plants with narrow leaves, tiny leaves, succulent leaves, fuzzy leaves, silvery leaves, hard leathery leaves and/or needles. These adaptations help plants conserve water.

Native oaks, toyon and lemonade berry are among the most common and sturdiest of the natives to use as background trees and shrubs. Against their deep green, plant silver-leaved succulent Dudleya rosettes, yellow flowering bladderpod (Peritoma arborea), and lavender-flowered chaparral mallow (Malacothamnus fasciculatus).

From Australia, plant flame tree Brachychiton acerifolius, any of the wonderful, flower-filled Grevillea — they are all hummingbird magnets — and black and yellow flowered black coral pea vine (Kennedia nigricans, hard to find but worth the search).

Every garden needs drought-tolerant trees — as many as possible. Strawberry tree Arbutus Marina has gorgeous shreddy, mahogany-colored bark with bright green leaves and pink flowers in spring. Gold medallion tree (Cassia leptophylla) is a narrow, medium-size tree with bright yellow flowers that turn into long, festive green bean pods. Tecate cypress (Hesperocyparus forbesii) is a Southern California native that is rare in habitat but readily available in nurseries.

Succulent aloes put on a beautiful show this time of year. One of my favorites is Aloe rubraviolaceae, a low-growing rosette type whose teal leaves are edged in soft rose. Each rosette features a single, tall candelabrum of stout, poker-style flowers that bloom red-orange.

Try some different succulents in your landscape. Furcraea mcdougalii grows up to 20 feet tall. It has a tall gray trunk, atop which it looks like an olive-green agave. Furcraea bedinghausii is another giant; this one grows up to 15 feet tall with a trunk topped in tall, blue-green blades. Furcraea foetida is a shorty, only 3 to 5 feet tall and 3 feet wide, with flexible, bright green blades. Its cousin, Furcraea foetida, has delightful yellow and green stripes.

Visit your favorite nursery for bare-root blueberries already available. Reserve bare-root fruit trees and shrubs that arrive next month: pomegranates, figs, peaches, apples, nectarines, pears, apricots and more.

Prepare for cold

Though we don’t get hard frosts, plants from coast to mountains can suffer frost damage on a cold night.

Protect cold-sensitive plants such as Plumeria, bromeliads, some kinds of succulents, etc. Move potted plants under the eaves or under low branches of evergreen trees. Cover in-ground plants with floating row cover (not plastic and not a bed sheet). Use clothespins to secure the cover in place.

Do not cut off the damaged parts of a frosted plant — they protect the rest of the plant from the next freezes. Wait until February or March, once the danger of frost has disappeared.

Fruit trees

This is the most important maintenance time for deciduous fruit trees such as peaches, nectarines, pluots, apriums, apples and others that drop their leaves in winter.

Between now and the end of January:

Strip leaves off the branches of stone fruits, pears and apples if they don’t fall off on their own. Leaves can be infected with fungus and other pathogens that overwinter. Don’t compost them. Rake them up instead, then send them off in the green waste.

Prune deciduous fruit trees, taking care not to cut off the fruiting wood. Different kinds of fruit trees form fruits on different parts of their branches. Apples, for example, grow short spurs along the branches. Those spurs make flowers and fruits. Pomegranates and figs fruit at the end of branches. Pluots fruit along the length of the branch. Know what the fruit is before you cut.

My favorite pruning guide is “How to Prune Fruit Trees” by R. Sanford Martin.

After pruning, spray fruit trees to kill overwintering pests and diseases. Spray each treatment once, wait two weeks, spray again, wait two weeks and spray a third time.

Spray apple and pear trees with mineral-based horticultural oil to suffocate scale, whiteflies, mealy bugs and other tiny pests that overwinter in the bark.
Spray stone fruits (peach, nectarine, plum, etc.) with liquid copper to kill the fungus responsible for the dreaded peach leaf curl. Spray mineral-based horticultural oil, too.
Every time you spray, coat all branches and trunks, from tips to base. The better the coverage, the more your trees are protected.

If you have lots of fruit trees, consider a battery-powered sprayer. Such a sprayer is more expensive than a hand pump but is easier to use and much faster and more effective.

Care for potted plants

Remove the foil as soon as you get a poinsettia home. Place it in a bright room away from heater vents and cold windows.

It’s poinsettia time! Remove the fancy foil as soon as you get the poinsettia home. Make sure its pot has drainage holes. If it doesn’t, move the plant to a new pot with drainage. Place it in a brightly lighted room away from the heater vent and away from a cold window. Water enough to keep the soil damp but not wet. Don’t fertilize until after the holidays.

Monitor potted plants. Feel the potting soil every few days and water before the soil gets too dry. A humidifier can help keep indoor air moist and plants from drying out.

Control pesky little black flies. These fungus gnats are attracted to wet organic matter in the potting soil. They are easy to control without chemicals or sprays if you water less (your plants will be fine) and cover the surface of the potting soil with a half- to 1-inch-thick layer of small pebbles, aquarium rocks or even marbles. They form a barrier the flies can’t penetrate.

Edible gardens

All summer vegetable plants should be removed by now. Even if your tomato or pepper continues to produce, next year it won’t be nearly as productive and vigorous as this year. Pull them out and start again in the spring.

Before you replant pots or raised beds, add compost to bring the soil level back to the top. Sprinkle in earthworm castings and vegetable fertilizer.

Plant winter root vegetable seeds (not seedlings) now: beets, turnips, radishes, carrots, rutabagas, parsnips.

Plant greens and cabbage family plants from seed or seedling: lettuce, spinach, kohlrabi, kale, Brussels sprouts, cabbage, cauliflower, broccoli and more.

Plant annual parsley, dill and cilantro from seed. These annual herbs do best in vegetable gardens.

Plant perennial oregano, thyme, marjoram, sage and rosemary from 4-inch or 1-gallon pots into a permanent spot in the garden. Since they are all waterwise Mediterranean natives, plant them in ornamental garden beds.

To harvest greens such as lettuce, kale, spinach, bok choy and tatsoi, cut off as many leaves as you need and let the plants continue to grow. Harvest herbs the same way.

Mulch

How thick is your garden’s mulch? Aim for a minimum of 3 inches over every garden bed. Be sure irrigation lines are under the mulch, not on top.

Mulch succulents with rock or gravel. Mulch non-succulents with aged woody mulch or fresh wood chips that are smaller than an inch. Larger fresh wood chips can bring deadly borers into your garden. Aged wood chips are not problematic.

Nan Sterman is a garden designer and writer and the host of “A Growing Passion” on KPBS television. For more information, visit agrowingpassion.com and waterwisegardener.com. ◆

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