Download a printable copy of our DECEMBER Gardening “To-Do” Checklist.
Trees and Shrubs
- To reduce the chances of damage by rodents over the winter, clear away weeds and dead leaves from around the base of shrubs and trees, especially fruit trees.
- Pruning of spring-blooming deciduous (leaf-dropping) trees and shrubs should be limited to removing dead, broken or diseased branches. (Major pruning of spring-bloomers should be done soon after blooming; that way you get to enjoy the blooms.) It’s fine to take some trimmings from your evergreens for holiday decorating, though. Hollies, boxwoods and pines are great for this.
- If we have a heavy snow, try to keep it from building up on the gutters and eaves above shrubs. Also use an upward motion to gently sweep snow off the shrubs to prevent breakage.
- It’s good to apply 2-3 inches of mulch this month if you haven’t done it already; just be sure to keep it away from the trunks of trees and shrubs.
- Newly planted or young trees can be fertilized this month, as long as the ground isn’t frozen. Their roots continue to grow over the winter and benefit from the feeding. Mature trees generally don’t need to be fed.
- If we have a dry spell of several weeks, water your newly planted trees and shrubs, especially the broadleaf evergreens like rhododendrons, azaleas and cherry laurels.
- It’s still okay to plant trees and shrubs this month, as long as the ground isn’t frozen. However, it’s too late to transplant trees and shrubs from one spot to another in the garden – they wouldn’t have enough time to recover before severe winter temperatures.
- It’ll soon be time to spray anti-dessicants on your evergreens for the winter to help prevent wind-burn. Products such as Wilt-Stop and Freeze-Pruf work well to minimize leaf browning due to low temperatures and excessively dry air that pulls the moisture from the leaves. A light coating will do the trick for your broadleaf evergreens such as azaleas, rhododendrons, camellias, hollies, boxwood, mahonia, leucothoe, etc. (Spray the foliage once the temperatures stay cold and follow bottle instructions as to how lightly or heavily to coat the leaves.)
- Every year after a heavy snowfall we’re asked about Japanese Maple branches that break due to the weight of snow. So here’s the way to prevent damage to them: Make sure there is no accumulation of leaves on branches. You can even do what they do in Japan – support branches with a board that has a V notch cut in it, then wrapped in burlap (to avoid abrasion to the branch).
Perennials, Annuals and Border
- Now’s a good time to collect free seeds from your own garden – from plants like cleome, zinnias, cosmos, celosia and butterfly weed.
- If you apply compost now to your borders (and we love Maryland’s own 100% organic Leafgro) – it’ll have plenty of time to enrich the soil before spring.
- Evergreen perennials like hellebores prefer sunlight to being buried under six inches of wet leaves for the winter, so remove leaves from around and on top of them. Also, remove leaves from near creeping and woodland phlox.
- If you didn’t get around to putting your potted perennials in the ground, don’t panic. Our perennials specialist Larry Hurley has found that most pots of perennials overwinter quite well if placed on the ground and covered with 8 or 10 inches of leaves, preferably oak which doesn’t mat down as badly as maple. Uncover the plants in early March.
- If you have lavender in your garden, it survives the winter better if mulched with gravel rather than bark mulch – because lavender hates soggy soil and moisture around the stem. White marble chips are a good mulch for lavender because the dust reduces soil acidity, something else that’s good for lavender.
- If you still haven’t found time to plant your tulips, it’s not too late. They’ve been known to still bloom in the spring in our area despite being planted as late as January.
Indoor, Seasonal and Overwintered Plants
- Check overwintered plants in the basement or garage to see if they need watering.
- Check your houseplants monthly for possible pests like scale, mealybugs and spider mites. They’re easier to control if you catch them early – with a water spray or insecticidal soap. If both those methods fail, use a Q-tip dipped in alcohol to swab away the offender.
- Be careful NOT to overwater. With reduced light, your houseplants really don’t need as much water. Let the soil dry out between waterings.
- And don’t feed your houseplants during the winter – unless they’re growing under optimum, high-light conditions.
- If you’ve potted up amaryllis bulbs, wake them up by watering once, then putting them in a spot with bright light and waiting for them to respond. Water again in two weeks if they haven’t responded yet.
- If you didn’t cover your pond to prevent leaves from falling in, remove the leaves from the water now. (If you don’t, the decomposing leaves will produce gases that get trapped under the ice and can sicken or kill your fish.) Cover the pond with screen after its been cleaned.
- Stop feeding your fish – they can’t metabolize food easily during cold weather, and that can make them sick (or worse).
- Give local birds a break by providing (unfrozen) water for them all winter, and food, too. And leave the seedheads of your black-eyed susans and coneflowers up for them to munch on.
- Join Project Feederwatch and start counting birds – for fun and science!
- Winter is when deer get desperate and target some of our most expensive plants – the shrubs and trees. So don’t stop spraying them with deer repellent. Put it on your calendar so you don’t forget.
- If you feed the birds, clean up the bird seed hulls under the feeder. Sunflower seed hulls suppress plant growth and can stunt your perennials if they collect under the feeder.
- Put your hummingbird feeder away for the winter. They went South.
- Keep fallen leaves off your lawn. Mowing them with a mulching mower (one with a bag) is a great idea because you can then compost the chopped-up leaves or apply them as mulch. If your mower doesn’t have a bag, just leave the chopped up leaves on the lawn to feed your turfgrass; mow over them twice to ensure nice small bits that will decompose quickly.
- It’s too late to fertilize – wait until spring.
Vegetables and Herbs
- Protect beets, spinach, lettuce, broccoli and other cool-season greens that have already germinated in the fall garden with a cold frame, plastic sheeting or floating row cover. And remember to vent the cold frame or plastic cover on sunny days to prevent heat build-up.
- You can over-winter carrots, parsnips and turnips by covering the bed with a deep straw or leaf mulch. Just pull them up throughout the winter when you’re ready to eat them.
- Keep garden beds covered with shredded leaves or mulch to minimize the risk of soil erosion and nutrient run-off.
- Store dried herbs in a cool, dark location away from the stove but in full, direct sunlight (or give them 14 hours of fluorescent lighting each day).
- Applying compost now to your vegetable garden – like Maryland’s own 100% organic Leafgro – will give it plenty of time to enrich the soil before spring.
- Have you turned off your outdoor hoses, brought your non-weatherproof pots indoors yet? Get on it!
- Good time to take the mower in for service after the final mowing – before the spring rush. Then store without gas in the tank, by running it dry.
- Do NOT use fertilizer to melt ice – it pollutes our watershed and can damage concrete, metal and plants.
All that said, Behnkes staffer Susan O’Hara has this answer to the question of what to do in the garden in December (and who can argue with it?)
It’s December. Enough said. Spend much time enjoying the company of friends and family. Even in this economy, we can all do that. Money’s too tight for buying gifts? Give the gift of yourself. Rake someone’s leaves; take out your elderly neighbor’s trash; drive your mom through the neighborhood to look at the lights. Make memories.