3810 Whites Creek Pike, Nashville, TN 37207 (615) 876-1014

Archive date:  January 8, 2010

The Big Chill

Mother Nature does most of the protection, but you can help

After a solid week of sub-freezing temperatures, you’re probably wondering how your plants are faring. Fortunately, they are well equipped to deal with what weather we have had…so far. Plants must deal with freezing water at the cellular level (I’m not talking phones here), the way different plants deal with the water within their cells can be quite different.

Typically the roots are protected by the earth itself. Only the top couple of inches of soil reach extreme temperatures (close to air temperature). If you go just a bit deeper than that, the soil won’t get much colder than 28 or 29 degrees. This is very tolerable for most plants. There is an area of exception: Containerized plants.

Containerized plants are used widely and quite successfully in the south. The problem exists due to the fact that the soil is entirely above ground, therefore it will freeze much more quickly and at lower temperatures than plants growing in the ground. It is imperative to make sure plants in containers are thoroughly watered just prior to and immediately following severe freezing conditions. Wet soil insulates better than dry soil. Since we have already passed the time to water prior to cold, make sure you water your container planters early next week as the weather warms. Many plants will suffer some damage when the SOIL temperature (not air temperature) goes below 17 degrees. It may be possible for you to insulate your containers by wrapping with blankets or insulation or if possible, pull them into the garage or basement, where the temperatures are less severe.

Annuals produce many seeds to perpetuate themselves into the next season. Before they disperse their seeds in the fall, the plants pull water from the seeds. When the low temperatures come, there is very little water to freeze, swell and rupture the cells within the seeds.

Perennials deal with winter by letting the cold kill off the parts of the plant above the ground. The roots survive the winter. Sugars in the roots of perennials act as a kind of natural antifreeze by lowering the freezing point below 32 degrees. In addition, water can be moved out of cells into the surrounding areas. That allows the cells to accommodate a degree of freezing and expanding without rupturing the cells.

It's a good idea to spread 3 inches of hardwood mulch or straw or leaves over your perennials to give them an added layer of protective insulation.

Deciduous trees lose their leaves every year. As with the roots of perennials, the trunk and limbs of trees are protected by "antifreeze" sugars and the movement of water out of cells; the trees also draw water out of their buds. The reason late spring freezes are so damaging to trees like Japanese maples is that the water has already begun to return to the buds.

Even though they adapt well, trees can still be damaged by freezing and thawing. It's normal for some water to freeze inside tree trunks during the winter. As many of us experienced in 2007, greatest damage likely occurs during late spring freezes that follow unusually warm weather arriving early.

Conifers, such as arborvitae, juniper, yew, pine and spruce, don't lose their needles because they have so much natural antifreeze in them that they're unlikely to freeze. But while the needles don't drop off, they can lose moisture to the winter winds. Occasionally we experience browning on evergreens caused by desiccation (drying out of foliage).

Perhaps this is the worst that winter will deal us this winter. Be prepared! There is no guarantee of that. Low temperatures for the next two nights are forecast to be in the single digits. One thing to note: Plants do not feel “wind-chill”, that is reserved for us mammals. Do not let “wind-chill” forecasts overly alarm you with regard to your plants…but the wind does dry them out so don’t forget to water when the weather warms.

We are reducing our hours for the next two days. We will be open from 8am to Noon Friday 1/08/2010 and CLOSED Saturday 1/09/2010.

Stay warm,

David Bates