It’s the second weekend in January and there are still green plants in the garden; tanacetum, digitalis, oriental poppy foliage, arum italicum and of course, a good selection of weeds. We have not had a killing frost and we did not have a white Christmas. Snow is predicted for large parts of the area, but we will likely get rain. A light snow that melts quickly would probably leave those plants green. However, snow, after the ground has frozen, can actually be good for plants. Many of us welcome those warm spells in the winter but consistent cold is also better for plants.
Plants that are hardy in this zone have begun dormancy. Deciduous trees have shed their leaves and stopped growth in preparation for a season with little water. The above ground growth of herbaceous perennials has died and the roots have become dormant. Bulbs are ready for a period of rest before their spring show. They all need a winter with consistent very cold weather to thrive next year. Freeze and thaw periods can harm and even kill plants. This contracting and expanding of soil causes heaving of plants and root damage. Periods of unusually warm weather in winter can cause plants to break dormancy, buds to open, and even new leaf growth. If followed by extreme cold, this new growth will be killed and this stress for plants can affect their health next year. A consistently cold winter is best for plants.
A good layer of soft snow is beneficial for plants. Because air fills the space between snowflakes, snow is a good insulator, helping to regulate soil temperature. When melted, it provides moisture to the soil and helps break up soil particles. It is called the “poor man’s fertilizer.” Nitrogen and sulfur attach to snowflakes and enter the soil as it melts.
Snow and cold weather also kill many insects. Following the warm winter last year I got more ticks than any other year and my poor husband was attacked by more chiggers and mosquitoes than ever.
With a heavy or wet snow, trees and shrubs can use some help to get it off. Snow on trees with hanging branches, pines for example, can be shaken off. Use a broom underneath the branch and shake gently. The multiple trunks of arborvitae and Leyland cypress should be cabled or tied together to prevent them from opening. Snow should be brushed from boxwoods, yews, camellias and Japanese hollies. Do not break ice from branches as this can cause them to break. Sun the next day will usually melt it. When shoveling or blowing snow, do not pile it onto shrubs. Avoid getting salt on all plants.
Cold weather can damage potted plants in freeze-thaw cycles. Put all pots (even “weather-proof” pots) on feet. Move them, if possible, to a sheltered location. If one is not available, wrapping with bubble wrap will offer protection. Do not cut them back until spring.
In my garden, I do not cut any plants down until spring. Dead top growth helps protect the crowns. I also cover the beds with the leaves from trees on my property. (I throw no leaves away in the fall.) Mulch helps protect the plants and soil from temperature fluctuation. Evergreen branches on the beds are good protection and also hold snow to the ground.
Unfortunately, we will probably have a warm winter again this year, though with the unpredictable weather caused by climate change, perhaps not. Many plants in this area were severely stressed by Superstorm Sandy, even more than from last year’s hurricane, I think. As I drive around, I see many evergreens with brown sides that faced the wind. A winter with consistent temperatures and some fluffy snow would help them recover.
There is one benefit from the warmer winter temperatures that I like. We can push the growing zone from 7 to 8. In the past I have grown Ligularia “Spotted Leopard “and also “Giganteam” with a heavy layer of mulch. I think that this year I will try Colocasia “Black Magic,” maybe even Brugmansia “Charles Grimaldi,” both are zone 8 plants. I’ll also try one of my favorites, Zantedeschia “White Giant.”
Jeanelle Myers is a professional gardener and consultant. For gardening discussion you can call her at 631-434-5067.