Gardening Notes for December

The hustle and bustle of the Holiday Season is finally upon us! November provided plenty of moisture, minimizing any worry for watering newly installed plants or evergreens. The temperatures were also warm, providing good root growth. This is the time to properly prepare the garden for winter as autumn truly bids us farewell and the sub-freezing temperatures of winter are just around the corner. As time permits between the cooking and the ‘online’ shopping, continue your ledgers with notes on the weather and how plants are performing. Wishing everyone a very Happy and Merry Holidays!

Things to do:

• • Finish removing leaves from lawn areas. If possible, shred the leaves with the lawn mower and add them to perennial or annual beds as mulch. The shredded leaves that remain in the turf are actually very beneficial for the grass.
  • Many people think that the decaying leaves look unattractive and should be removed from beds around the home. However, the leaves, whether shredded or whole are very important to our biosphere and should be used as mulch wherever possible!
  • If you have water features or ponds, keep the leaf nets over the pond at least through months’ end or until prolonged subfreezing temperatures are predicted to keep any leaves that are still blowing about from getting into the pond.

• • Decorate those plastic and fiberglass containers or window boxes that can remain outdoors for the winter. Evergreen boughs such as Yew, Pine, Hemlock, Juniper Southern Magnolia, Holly or Cherry Laurel can be pruned from the garden to decorate the container. For large pots, add containers of red stemmed Dogwoods (Cornus sericea or Cornus sanguinea) or Willow (Salix alba ‘Britzensis’ or Salix x ‘Swizzlestick’) for their glowing red stems. The dancing stems of Salix x ‘Swizzlestick’ are pictured at right. Add some white painted birch stems, which many Garden Centers carry and an attractive winter container will result! Come spring, the containers of woody plants can be removed and added to strategic locations within your garden.
  • If you have recently planted an evergreen, make certain that the soil remains moist in case we have several weeks without another rainfall. A 3-4” layer of mulch over the roots certainly helps to retain the moisture and will moderate the depth to which the soil will freeze, reducing the plant’s ability to absorb water.
  • Rhododendrons, Holly and other broadleaf evergreen shrubs that have been planted this fall will benefit from an application of an anti-desiccant spray. Apply during periods when the temperatures are above freezing for several hours and continue to reapply as temperatures permit though the winter according to directions.
  • Finish cutting back those perennials which have collapsed to the ground, especially around the base of newly planted trees. The debris acts as a veil for hungry mice during the winter who enjoy eating the tree bark throughout the winter.
  • By the same token and wherever possible, leave the stems and seed heads of Black Eyed Susan (Rudbeckia), Cup Flower (Silphium), Purple Cone Flower (Echinacea) and similar flowers standing for the winter, since the seeds provide food for the birds and the hollow stems habitat for beneficial insects!
  • Equally as important, allow hollow stemmed shrubs such as our native Hydrangea (Hydrangea arborescens) and Elderberry (Sambucus canadensis) to remain standing through the winter and refrain from cutting off dead wood where possible. The hollow stems serve as a winter home for our beneficial insects as well as a location to lay eggs in the season to come.
  • Finish digging up Canna and Banana tubers, letting the soil dry so it can be knocked off once brought into the garage and then wrapped and stored in a cool basement.
  • Finish gathering seed from various annuals that are not hybrids as they will come true from seed. Dry and place in labeled packets for sowing come spring!
  • Remove the old foliage from Bearded Iris (Iris germanica) that is now shriveled, brown and laying on the ground. These leaves harbor potential egg masses from the Iris Borer that were laid by the adult moth and are poised to hatch and enter through the flower stem come May.

• • Bearded Iris is not the only Iris that should be cleaned up for winter, as it is a good idea to remove the foliage from most all the Iris for the winter. They may not be subject to the Iris Borer, since they do not possess large rhizomes, but previous season’s foliage provides an ideal cover for winter roaming mice. The root systems of all Iris make a tasty winter’s snack! Iris tectorum (Japanese Roof Iris) is picture above.
  • Consider edging bedlines if the ground is not frozen and time avails, as it will be one less item to consider come the spring! In general, it is easier to dig in the fall since the soil is not as damp. Do not dig the edge of the bed too deep, as lawnmower wheels are likely to fall into the trench and scalp the lawn.
  • Pot-up daffodils, tulips or minor bulbs into shallow pots and place them in the back of an unheated or minimally heated garage for the winter. Water when the soil appears dry. As the shoots begin to appear in February, place them in a sunny but cool window. They will provide nice early color to the kitchen table in March or for outdoor containers in March, April and May.
  • For Tea Roses, mulch the graft union with soil, leaves or shredded bark after the soil has started to freeze. This will ensure that the named selection that has been budded onto a rootstock will not perish during the winter. It is often beneficial to partially prune Tea Roses back to reduce any potential wobbling due to winter winds. Complete the pruning come spring.
  • Winterize lawn mowers and other gas-powered equipment. This entails cleaning or replacing the filters and amending the fuel with an additive that will prevent it from becoming more viscous and potentially blocking fuel lines come spring.
  • If there is access to composted or even fresh horse or cow manure, it can be spread now in the annual beds (not vegetable or perennial). Shredded leaves can be spread as mulch for vegetable gardens if there was not sufficient time to sow a cover crop as it adds organic matter back into the soil.
  • Finish cleaning out old plants from the vegetable garden and take note of where various plants were located this past year allowing for crop rotation, even if on a minimal scale.
  • Continue to adjust houseplants that prefer less direct sunlight as the sun continues to dip lower in the sky and reach further into the room.
  • Take inventory of potting soil, seed starting materials and gardening tools. If some of your inventory is in need of replacement or updating, they might make good Holiday gifts should you be that person who already has everything!
  • Evaluate the Garden to see if it is in need of additional December flowering or fruiting cheer! Plants like Mahonia x ‘Charity’ (pictured at right on November 23, 2019), Climbing Aster (Symphyotrichum carolinianum) and Witch Hazel (Hamamelis virginiana) are presently in full bud or bloom and Winterberry Holly (Ilex verticillata) is full of glorious red, yellow or orange fruit depending upon the cultivar! Ilex verticillata ‘Winter Gold’ is photographed at right.

Bruce Crawford
Program Leader in Home and Public Horticulture