December garden tasks: Southeast

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Freeze protection for tender plants

December cold snaps can drop well below freezing even along the coast. When one is forecast:

• Cover tender shrubs, tropicals and vegetables with cloth or frost blanket that reaches the ground. Water dry soil beforehand, and remove covers once it warms. Both UF/IFAS and UGA Extension give the same basic steps.
• Citrus: per UF/IFAS Extension in Okaloosa County, the graft union and lower trunk of young citrus trees can be protected by banking soil around them or wrapping them for the winter. Remove soil banks in spring. Pick ripe fruit before a hard freeze.
• Containers: move them against a south wall or into a garage. Pot-grown roots are the most vulnerable part of the plant.
• After a freeze, don't rush to cut back damaged plants. Wait until new growth appears in late winter or spring (see the January guide).

Irrigation and plumbing: turn off automatic irrigation before freezing nights. Water sprayed onto plants and walks just before a freeze turns to ice. In the upper zones, drain and store hoses, and insulate exposed backflow preventers and outdoor faucets. A broken backflow device is one of the most common and expensive freeze repairs in the region.

What usually doesn't need covering: established hardy shrubs (hollies, camellias, azaleas, boxwoods), collards, kale and pansies generally ride out normal winter lows. Spend your covers on recently planted shrubs, tropicals, citrus, lettuce and broccoli heads.

The winter vegetable garden

Collards, kale, cabbage, turnips, mustard, carrots and spinach keep producing through December in most of the region. Pick leafy greens from the outside in, and leave carrots and turnips in the ground under mulch until you need them. Throw row cover over lettuce and broccoli whenever a hard freeze is forecast.

• Zones 7–8: little new planting happens now. Focus on harvesting and protecting what is in the ground.
• Zones 8b–9: fast greens and radishes can still be sown in mild spells.
• Florida: UF/IFAS Gardening Solutions' "What to plant in December" lists the many cool-season crops that still go in this month, including broccoli, cabbage, carrots, lettuce and onions.

Garlic and onions: fall-planted garlic and onions should show green tops by now. Keep the beds weeded. Garlic competes poorly with weeds, and winter weeds grow fast in mild spells. Top up the straw mulch if rain has thinned it. Don't fertilize them heavily now. A side-dressing in late winter, as growth picks up, does more good.

Broccoli side shoots: after you cut the main head, leave the plant in place. Most varieties keep producing smaller side shoots for weeks in mild weather.

Holiday plants and Christmas trees

Poinsettias: per NC State Extension, keep them in bright, indirect light, away from cold drafts and heat vents. Water when the surface feels dry, and poke holes in or remove the decorative foil so water can drain. UGA Extension gives similar advice for amaryllis, Christmas cactus and other gift plants. UF/IFAS covers which holiday plants are worth keeping and which can move outdoors in Florida.

Cut trees: NC State's Christmas tree program recommends making a fresh cut across the base just before you set the tree up. Use a stand that holds plenty of water, check it daily, and keep the tree away from heat sources. A tree that is allowed to dry out can seal over and stop taking up water.

December pruning rules

The rule this month is simple: hold off.

• Spring bloomers: azaleas, forsythia, loropetalum, spring-flowering camellias and other spring bloomers already carry their flower buds. Prune them right after they flower, not now.
• Camellias: Clemson HGIC notes that sasanquas bloom in fall and early winter and japonicas in winter to early spring. Prune each type after it finishes flowering.
• Crape myrtles: wait until late winter. UGA Extension calls December the start of "crape murder" season, when trees get topped back to stubs. Topping causes weak, crowded sprouts and knobby trunks, and it isn't necessary for flowering.
• Any time: remove dead, diseased or broken wood, including storm damage.

Lawns while warm-season grass is dormant

Brown bermuda, zoysia, centipede and St. Augustine are dormant, not dead. Don't fertilize them, and keep heavy traffic off frosted turf. Rake or mow leaves off the lawn so they don't smother it.

Winter weeds such as henbit, chickweed and annual bluegrass stand out against the dormant turf. Hand-pull small patches. If you use an herbicide, check that it is labeled for your grass type. Several common products injure St. Augustine and centipede. Clemson HGIC's annual bluegrass fact sheet explains why prevention next fall is easier than control now.

Tall fescue lawns in zones 7–8a stay green through winter. Keep fallen leaves off them, mow only when the grass actually needs it, and stay off when the turf is frosted. Footprints on frozen blades leave brown tracks. Ryegrass-overseeded bermuda lawns need occasional mowing in mild spells. Take a soil sample from any lawn that struggled this year, so you can correct pH and nutrients before spring green-up.

Planning, soil tests and bulbs

• Soil tests: if you didn't test in fall, do it now. There is still time for lime to start working before spring.
• Bulbs: finish planting spring bulbs this month. Per Clemson HGIC, December is the end of the window. Pre-chilled tulips can go in now in zones 8–9.
• Plan the spring garden: order seed catalogs and note which varieties did well and which didn't. Count back from your last frost date to set January seed-starting dates.
• Check stored produce: look over sweet potatoes, winter squash and saved seed, and throw out anything showing rot.

Keep planting trees and shrubs

Across most of the Southeast the ground rarely freezes for long, so dormant-season planting continues through December. A tree or shrub planted now spends the winter growing roots and has a head start before the first summer. Per Clemson HGIC:

• Dig the hole wide but no deeper than the root ball, and set the root flare at or slightly above the surrounding grade.
• Loosen or cut circling roots on container plants. They don't fix themselves once the plant is in the ground.
• Backfill with the native soil. Heavily amended planting holes can trap water in clay and discourage roots from spreading.
• Water thoroughly at planting and during dry spells all winter. Mulch 2–3 inches deep, kept off the trunk.

Winter is also when garden centers stock bare-root fruit trees, roses and berries. Plant them as soon as you can after buying, and keep the roots moist until they go in.

Pansies and winter color

Pansies and violas planted in fall should be blooming now in milder spells. NC State Extension's winter pansy care advice covers the basics:

• Water before a hard freeze if the soil is dry. Well-watered plants handle cold better.
• Expect flattened, wilted-looking plants after a hard freeze. They usually recover as soon as it warms. Covering them with pine straw or frost cloth during severe cold reduces flower damage.
• Pinch off faded flowers to keep new buds coming.

Camellias, hellebores and winter-blooming mahonia carry the garden through the darkest weeks. December is a good time to visit a public garden or nursery and choose varieties while you can see them in bloom.

Common mistakes

Frequently asked

How do I protect citrus trees from a freeze?

UF/IFAS recommends protecting the graft union and lower trunk of young trees with a soil bank or trunk wrap, watering beforehand, and covering small trees to the ground during hard freezes. Pick ripe fruit before a severe freeze, and remove soil banks in spring.

Is December too early to prune crape myrtles?

Yes. Wait until late winter, before new growth starts. And don't top them in any month. Prune only for structure.

Can I plant vegetables in December in the Southeast?

In Florida and along the Gulf Coast, yes. UF/IFAS lists many cool-season crops for December. Farther north, December is for harvesting and protecting crops already in the ground.

Sources

1. This Month in Your Garden – December 2023, Clemson HGIC
2. Protecting Citrus from Cold Weather, UF/IFAS Extension Okaloosa County
3. Cold weather expected: Should I cover my plants?, UF/IFAS
4. What to Plant in December, UF/IFAS Gardening Solutions
5. How to Care for Poinsettias, NC State Extension
6. Care for Your North Carolina Fraser Fir, NC State Extension Christmas Trees
7. Crape Murder Season Is Upon Us, UGA Extension
8. Camellia, Clemson HGIC

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