Monthly Gardening Calendar
Sharon Morrisey, Consumer Horticulture Agent
University of Wisconsin-Extension in Milwaukee Co.

December brings the year and the gardening season to a close. The consolation is that after the winter solstice on December 21st, the days are steadily getting longer!

The holiday season brings many opportunities to decorate with plants. Buy or cut-your-own fresh Christmas tree. Bring it home inside a vehicle out of the wind or wrapped in a sheet or tarp. Be sure to re-cut at least 1” off the trunk just before placing it in the stand so it can absorb water. Keep it watered; never let it dry out. Check the water level twice a day at first since it can use between a pint and a gallon of water a day.

Buy bundles of greens or lightly prune some of your own needle evergreens to make wreaths and holiday decorations. Fresh cut evergreen wreaths, garlands, and swags are probably best as outdoor decorations for longevity and safety. Arborvitae, pine, fir and juniper are the most long lasting choices. A few stems stuck into bare planters left outside make them more attractive for the winter.

Indoors poinsettias, azaleas, amaryllis and Christmas cactus are beautiful living decorations. The latter two are the easiest to keep thriving and to flower again next year.

The gardeners on your Christmas shopping list should be easy to buy for. There are tools, gloves, kneeling pads, books and on and on and on. Consider gift memberships to public gardens or nature centers. In Milwaukee County, Boerner Botanical Gardens, Wehr Nature Center, and the Mitchell Park Domes are a few favorites where gardeners and non-gardeners alike learn something new every time they visit.

Calendar entries followed by a number in parenthesis, have corresponding UW-Extension InfoSource messages that will provide you with further details on that subject. In the Milwaukee area call 414-290-2450 and then follow the simple instructions. Outside of the Milwaukee area, call 1-800-441-4636.

First Week

Finish garden and yard clean-up chores such as removing infected plant debris from perennial and vegetable beds. Chop the last of the fall leaves lying on the lawn by mowing over them several times so they simply filter into the lawn rather than matting on top.

Move plastic and clay planters indoors for the winter to prevent them from cracking. Wooden barrels and concrete planters can be left outside. Leave the soil in place to prevent barrels from drying and shrinking.

Remove tall grass and weeds from the bases of trees, too. Protect trunks of young trees by wrapping. Spiral plastic trunk barriers or hardware cloth close to the trunk are the best options. Surround multi-stemmed and low branching trees and shrubs with chicken wire or hardware cloth held securely against the ground. It should be tall enough to protect branches as high up as a rabbit can reach when on its hind legs on top of a snow bank.

Combine several tactics to scare away animals that can damage your plants in the winter. Shiny, noisy, moving objects hung in the garden along with bags of human hair or soap can be used in addition to commercial repellents or ones prepared at home. Remember to reapply these substances often since most of them lose their potency quickly.

Check your yard, garage or tool shed for garden products and equipment that should be stored indoors for the winter. Liquids should not be allowed to freeze. Pesticides should be stored locked, out of the reach of children, and in their original containers. Plastic sprayers and rubber and vinyl hoses should be stored empty, preferably indoors.

Winterize your lawn mower by running the engine dry, draining and replacing the oil, cleaning the air filter, oiling the plug, and wiping clean the engine. Now is a great time to take it in for a tune-up and blade sharpening so it’s ready as soon as that first surge of growth comes in the spring.

 

Second Week

If the ground is finally frozen an inch or so deep, it is now safe to apply winter mulches to newly transplanted or tender perennial flowers, roses and strawberries. This will insulate them from the cold above ground and help reduce the fluctuations of temperatures in the soil throughout the season, which can heave their root balls right out of the ground.

Surround rose bushes with chicken wire cages and fill with up to two feet of chopped, dry leaves to protect them for the winter. Cover the base of the stems with several inches of soil or compost first and then place the chicken wire on top of the mound after it has frozen. Tie canes together with cloth strips or nylons to keep them from rubbing when they are blown by the wind. Leave them uncut, however, until next spring when you will know how much was killed and therefore how much to prune out.

Pile soil or compost over the crowns of marginally hardy or very exposed garden chrysanthemums. Then add 2" of mulch on top. For all mums, do not cut off dead stems until next spring.

A thick layer of straw over root crops like potatoes, parsnips, and carrots as well as parsley and leeks will protect them long enough to harvest them a little at a time well into the winter.
 

Third Week

Cyclamen, Christmas cactus and azaleas are good choices for people who keep their houses cool. Also look for Jerusalem Cherry, ornamental peppers, and kalanchoes. Be sure to cover these during transport even a short distance - most are very sensitive to temperatures below 50 - 55 degrees.

Floral arrangements should be kept cool and out of the sun. Contrary to common belief, arrangements and cut flowers should be watered with very warm water which contains floral preservative. Re-cut flower stem ends first and then condition them in a very cool spot for several hours before bringing out into warmer rooms. Every couple of days, re-cut the stem ends, wash the vase with soap, and refill with warm floral preservative water. Substitute non-diet lemon lime soda or vinegar and a drop of bleach if you don’t have preservative on hand (not an aspirin, a penny nor a nail as is sometimes recommended. These don’t work.)

Check stored vegetables like tomatoes, potatoes, onions and garlic and non-hardy bulbs like canna, tuberous begonia, dahlia, and gladiolus for mildew and rot. Remove affected items immediately.

Avoid rock salt, which is sodium chloride, to melt sidewalk and driveway ice. Products made of calcium chloride or potassium chloride cause less damage to plants. For traction, sprinkle sand, kitty litter, or wood ashes. Mix with a little melting compound if more than just traction is needed.
 

Fourth Week

Watch your new holiday gift plants closely and move them if they seem to be suffering in the spot you chose for them. Most of them need bright but indirect light and must be kept out of drafts as well as away from the hot air from heat vents, fireplaces, and TV's.

Adjust your indoor plant watering practices as needed according to the weather conditions. The shortest day of the year is December 21st and the reduced light slows plant water use and therefore also fertilizer use considerably.

Groom indoor plants to clean leaves, remove fallen leaves and faded flowers. Cleaning removes dust, spray materials, and grease that can clog leaf pores. Hand dust large-leaved plants with a pair of old socks or gloves on both hands. Put a group of plants in the shower if hand washing is not possible. Cover large areas of exposed soil with foil or plastic.

Clean garden tools with a wire brush and apply a light coat of oil to protect them from rusting. Sharpen edges of hoes and spades. Clean, readjust and sharpen the blades of pruning tools.

Mulch strawberries with straw, leaves, or evergreen boughs. Mulch needs to be 6" deep after it has packed down. Branches cut from a discarded Christmas tree are perfect either as the mulch or to prevent straw or leaves from blowing away.

Shield broadleaf evergreens like rhododendrons and boxwoods from sun and wind. Evergreen boughs stuck stem end into the ground can protect small plants without looking too unnatural. Or use burlap and stakes to loosely surround but not completely cover them especially on the windward side.

Evergreens growing close to roads where fast moving traffic produces a salty spray over the winter should also be protected.

Do not prune trees or shrubs until the end of the dormant season or just as growth resumes in the spring.

Delay pruning of raspberries and grapes until early next spring. Bearing canes of summer-bearing raspberries should have been pruned down to the ground after harvest this summer. Ever-bearing raspberries can be pruned to remove all canes after the fall crop, which will help minimize the carryover of disease problems. Managed this way, only a fall crop will be produced but it will be more fruitful than if they are grown for two harvests a year. Prune back the tips of all canes next spring regardless.