Here’s your December gardening guide for North America’s USDA Plant Hardiness Zones: 3-10. If you don’t know what USDA Plant Hardiness Zone you live in, check the map here to find out. We’ve left off zones 1–2 (far-north Alaska) and zones 11–13 (small section of the Florida Keys, the Pacific coast between L.A. and Mexico, and Hawaii) since zones 3–10 cover 99 percent or more of the gardeners in the U.S.
- Check your leftover seeds and make a list of what you need before ordering.
- Order seeds and plants early to avoid substitution.
- Take cuttings from fruit trees for grafting in April. Wrap the twigs in a wet paper towel, seal the wrapped twigs in a plastic bag, and store the bag in the freezer until spring.
- Organize your seeds: Discard those that are too old; then make a list of seeds to order.
- Order seeds of onions, geraniums, and other slow-growing plants now so you receive them in time to start indoors next month.
- Draw your garden plan.
- Check the condition of your gardening equipment.
- Build a garden trellis.
- Surprise your friends by harvesting Jerusalem artichokes and parsnips from the garden during a January thaw.
- Start seeds of pansies, snapdragons, and hardy perennials.
- Replenish your supplies, including seed-starting mix and organic fertilizers.
- Where there isn’t much snow cover, push back any plants that have “heaved” out of the ground because of freeze-thaw cycles.
- Start a collection of scented geraniums by taking cuttings from a friend’s plants.
- If you’re growing geraniums indoors in pots, cut back leggy stems by about half, re pot the plants in fresh soil, and then set them in a cool, bright window.
- Study the “skeleton” of your landscape and decide where to put new structures, such as pathways and arbors.
- Keep bird feeders well stocked with favorites, such as black oil sunflower seeds.
- Discard old seeds for the garden; mail orders for new seeds.
- Create a computer database of your garden plants with notes on performance.
- Rake heavy snow off shrubs.
- Start seeds of pansies, dusty miller, browallia, begonias, snapdragons, and delphiniums indoors under lights.
- At month’s end, start seeds of onions, leeks, broccoli, cabbage, and cauliflower indoors under lights.
- On mild days, remove winter weeds, such as wild onions and chickweed.
- Sow seeds of Shirley poppies (Papaver rhoeas) for bloom in May and June.
- Sow larkspur seeds directly in flowerbeds where you want them to grow; look for blooms by midspring.
- Indoors, start seeds of perennials or slow-growing annuals, like coleus and geraniums, beneath lights.
- Start seeds of cabbage, early lettuce, and at the end of the month, broccoli.
- When onion and cabbage transplants are available at the garden center, select the best ones, then plant them in the garden beneath a row cover.
- Near the end of the month, weed the asparagus bed and strawberry plot, then feed the plants and renew the thinning mulches.
- Shop local nurseries for asparagus roots, strawberry plants, and fruit trees.
- Cover root crops still in the ground with an extra layer of mulch.
- When cold temperatures are predicted, protect transplants of onions, cabbage, broccoli, and chard with a row cover.
- Sow beets, carrots, radishes, cress, bok choy, and garden peas directly in the garden; cover the planting rows with dark compost to warm the soil.
- Sow seeds of herbs, such as dill and parsley.
- Sow seeds of annual flowers (delphiniums, snapdragons, and larkspur are good choices) anywhere you want flowers for cutting or as a background for other plants.
- Top-dress lawns and garden beds with compost.
- Use the weather to your advantage: Observe the location of standing puddles left by winter rains; note where you need to improve drainage for plants.
- Finish pruning fruit trees, vines, and bushes.
- Sow seeds of geraniums, peppers, tomatoes, and eggplant in pots filled with a peat moss/vermiculite mixture; set the pots on a sunny windowsill or beneath lights until it’s warm enough to plant them outside.
- In the garden, “scratch in” wildflower seed mixes and California poppy seeds; plant nasturtium seeds a bit deeper.
- Set out transplants of pansies, calendulas, and primroses.
- As the soil warms, plant carrots, broccoli, lettuce, spinach, cilantro, parsley, and Asian greens.
- Harvest carrots, radishes, and Brussels sprouts—sweetened by frost.
- It’s the dry season—water vegetable plants, nondormant tropical plants, and bedding plants regularly.
- Spray compost tea on roses and bromeliads.
- Mulch peas to extend the harvest.
- Sow pumpkins and winter squash directly in the garden; start cucumbers and watermelons in pots.
- Sow quick-maturing varieties of carrots, broccoli, cabbage, coriander, parsley, and dill.
- Plant heat-tolerant chicory, lettuce, and Swiss chard in shade so that they stay cool when the weather warms.
- Snip off flowers of tropical fruit and young citrus to save their strength while they grow; bring the flowers indoors to perfume the house.