December Garden Calendar

Garden Help Desk

Master gardeners will take your gardening questions at the VCE Help Desk year-round. Give us a call. We will return to farmers markets in May 2020.

Ice Melters

Stock up before winter storms arrive. Ice melters help prevent falls, which can have serious consequences. However, all these products have drawbacks, particularly when over-applied. Avoid using ice melters that contain urea. Urea is an important nitrogen-containing ingredient in many fertilizers. But in winter, the soluble nitrogen will run off, polluting local waterways. Manufacturers often claim ice melters containing urea are completely safe for the environment; it’s not true.

Each of the ice melters listed below can damage asphalt and concrete.

  • Calcium magnesium acetate
    is safe for plants and pets. However, it is the most expensive option. It only works to 20 degrees F, and it can damage concrete that is less than one year old.
  • Sodium chloride (rock salt)
    is the cheapest alternative but probably has the most potential to harm plants and pets. It works to 20 degrees F.
  • Potassium chloride
    is the best option for surrounding plants and is reasonably safe for pets. It works to 20 degrees F.
  • Calcium chloride
    works fast and melts ice at temperatures as low as -25 degrees F.
  • Magnesium chloride
    works to -13 degrees F but can cause significant damage to surfaces.

Many of the commercial ice melters contain two or more of these ingredients. Read the labels on the bags before you buy, and read them again before you apply. If none of these options appeals to you, try coarse sand to improve traction on icy surfaces.

Trees & Shrubs

Leaf drop
Rake up and remove leaves from shrubs (such as roses) that have exhibited disease. These leaves are likely to contain spores that will re-infect the plants next year.

Deer protection
Commercial sprays have a good track record in repelling deer. Spray every two to four weeks, rotating among two to three products to keep deer from growing accustomed to the scents.

Snow and ice protection
Snow and ice can damage shrubs with multiple leaders, such as arborvitae and juniper. To prevent branches from bending and breaking, use cloth, nylon or garden twine to tie the trunks together above weak crotches. Remove the ties in spring.

Winter injury prevention
Evergreen shrubs in exposed areas may suffer desiccation from northerly winds or damage from bright afternoon sun on the southwest side of vertical trunks. Prevent both problems by surrounding the entire shrub or part of it with a burlap screen, making sure to leave the top open. Don’t use anti-desiccants, which have been found to be ineffective.

Watering
If weather remains dry, water deeply any trees or shrubs planted within the past year.

Pruning
The winter pruning season has arrived. Here is a partial list of trees and shrubs that may be pruned in December

  • Deciduous trees
    (engage a pro to prune large ones): Beech, birch, catalpa, elm, fringe tree, ginkgo, hickory, honey locust, linden, mulberry, black gum, oak, poplar, sourwood, stewartia, sweetgum, sycamore, willow, zelkova.
  • Evergreen trees
    cedar, cypress, fir, hemlock, holly, juniper, magnolia, pine, spruce
  • Shrubs
    arborvitae, boxwood, cherry laurel, clethra, cotoneaster, red twig dogwood, gardenia, juniper, osmanthus, photinia, mugo pine, privet, smoke tree, sumac, yew.

Prune all dead, damaged or diseased branches any time of the year.

Lawn

You can relax. There is not much for you to do.

Soil test
This is a good time to have your soil tested and to apply lime if the soil test indicates a pH that is too acidic. Lime acts very slowly so giving it the winter to raise pH is a good idea.

Winterize your mower
In November, you should have run all gasoline from the gas tank. Sometime during the winter offseason, drain and replace the engine oil, have your blades sharpened, and replace the air filter and sparkplug. With the sparkplug disconnected, clean any grass residue from the underside of the mower deck.

Vegetable Garden

Sanitation
Assuming you completed sanitation and top-dressing tasks in November, there is not much for you to do.

Fruits

Sanitation
Assuming you completed sanitation and rodent protection tasks in November, there is not much for you to do.
Do NOT prune fruit trees now; you will be pruning out the flower buds.

Houseplants

Watering
Most houseplants should be watered when the surface of the soil feels dry. Add water until it runs out the bottom of the pot. If the soil has pulled away from the pot’s rim, it is much too dry. Soak the pot in a bucket of water to restore the proper moisture.

Light
We won’t have enough natural sunlight to promote plant growth until to mid- to late-winter, when the sun is higher in the sky. Until then, use a grow light to augment sunlight but for no more than 16 hours per day.

Temperature
You might be surprised to find that the temperature on your windowsill is five to 10 degrees colder than near your thermostat. Therefore, if you keep your house at 65 degrees, it is possible that windowsill temperature may be as low as 55 degrees on cold nights. Almost all houseplants originate from the tropics and do not respond well to cold. Nighttime temperatures of 55 degrees may be lethal to some plants such as African violets. Close the window shades at night and make sure your temperature-sensitive plants are on the warm side of the shades.

References
A Guide to Successful Pruning, Shrub Pruning Calendar, VCE Publication 430-462
A Guide to Successful Pruning, Deciduous Tree Pruning Calendar, VCE Publication 430-460
A Guide to Successful Pruning, Evergreen Tree Pruning Calendar, VCE Publication 430-461
Best rock salt and Ice Melts Review, Consumer Reports, February 2014
Choosing Appropriate Ice Melt Products, VCE 2012
Managing Winter Injury to Trees and Shrubs, VCE Publication 426-500
Protecting Trees and Shrubs Against Winter Damage, University of Minnesota Extension
Annuals: Culture and Maintenance, VCE Publication 426-200