We are about two weeks into winter and up to this point it has felt fairly average for the Cincinnati area. But looking at the extended forecast the average weather we have experienced up to this point is about to change.
Below average temperatures are forecasted all throughout next week where the air temps will remain well below freezing for many days in a row. The very cold weather could have an impact on trees, shrubs, perennials and container plants in the landscaping.
there are steps that can be taken to protect these plants.
There are several actions that can be taken to minimize the damage to plants that can be caused by very cold air temperatures. These actions include:
- keeping plants watered, especially evergreens and potted plants
- adding an insulating layer of mulch above plant roots
- applying an anti-desiccant spray to evergreen plants
- protecting sensitive plants with a wind barrier
At the end of 2022, Cincinnati experienced an arctic blast that sent temperatures plummeting well below freezing for several days in a row. This weather event, coupled with drought conditions through the later part of the year, had devastating results on plants, especially many species of evergreens. The effects these weather events had on plants lasted well into the growing season – damaging evergreen foliage, causing die-back of branches, and in many cases killing plants.
Even in the winter time, plants need moisture in the soil to survive. This is especially true for evergreen plants that continue to lose moisture through leaves and needles in a process called transpiration. When cold winter breezes and winds blow, it draws moisture through tiny pores in needles and leaves. This is a useful mechanism for plants to move moisture and nutrients throughout the plant. However, if the soil is dry or the moisture in the ground is frozen from cold temperatures, the plant cannot replace lost moisture. The unfortunate result is the transformation of green leaves and needles to bronze or brown leaves and needles. In some cases damaged evergreen leaves and needles are replaced anew in the spring. In other cases branches of the plant are damaged and do not recover. And in more extreme cases, especially so with a borderline hardy plant, the result is a dead plant.
In autumn before freezing temperatures arrive and the garden hose is put away for the year, it is good to assess if the soil has sufficient moisture or if it is dry. If rain events have been frequent, then the soil is probably okay. If, however, the weather has been droughty, it is a good idea to give the soil around landscape plants one last thorough soaking before putting the hose away for winter.
A layer of mulch, one inch to two inches thick, over the root systems of plants does two things that help plants survive cold winter weather. First, it slows evaporation of moisture from the soil, retaining it to help replace moisture lost through leaves and needles. Second, it provides insulation from cold air temperatures. Even though above ground air temperatures may be well below freezing, it takes time for the cold air to penetrate into the ground. Mulch slows the transition, keeping roots safe from freezing temperatures. Be careful to not pile mulch around the trunk of a plant – mulch piled against the trunk of a plant can cause other problems.
Special care should be taken for plants (especially evergreens) that are kept in decorative pots and containers. If the container is light enough to move, temporarily take it into an unheated space such as a garage or breezeway, until outside air temperatures moderate. If this is not possible, water the soil around the plants well with cold water and make sure there is an insulating layer of mulch above the roots. Placing bags of mulch, soil, or leaves around the container will help with insulation. These can be used in the garden later in the year.
Evergreen plants in containers can be further protected by spraying the foliage with an anti-desiccant, such as Wilt Stop, or by temporarily wrapping with burlap. An anti-desiccant spray will slow or stop the loss of moisture through leaves and needles keeping them from drying out. Wilt-Stop is a brand of anti-desiccant that can be purchased at most independent garden centers such as White Oak Gardens. Apply according to the label. Temporarily wrapping burlap around a plant is another way to protect against leaves and needles drying out from wind. Burlap is preferred because it slows or eliminates cold breezes from reaching leaves or needles and allows for the plant to breathe – do not use plastic for this purpose.
Finally, perhaps the best way to protect landscaping against very cold weather is to choose plants that are known to be hardy and reliable. Popular plants of suspect reliability are laurels, Japanese hollies, crape myrtles, atlas cedars, cryptomeria, and Leyland Cypress to name a few.