Winter is here! The barren season. When the sky is bland and the trees look like they need a hug. Every year I learn more about the best methods for protecting my client’s and my own plants from the cold. Sometimes it’s a matter of trial and error, but it’s also about understanding the weather and planning ahead. Here is some information I’ve gathered along the way to help you maintain your yard this winter season and create a winter protection plan for your plants.
To understand how to protect your plants from cold weather, it’s worth it to first learn more about light frosts, hard freezes, and where they come from. Study your enemy! A light frost occurs when the nighttime temperature drops to 32 degrees or lower. Hard freezes are defined as a period of at least 4 hours when temperatures are at or below 28 degrees. Frosts and freezes will most likely happen on calm, clear nights when there are no clouds or wind. This is because of the transfer of heat from the ground to the atmosphere throughout the day and night. During the day, the sun warms the soil surface. At night, the ground radiates heat back into the cool atmosphere. Clouds deter frosts and freezes because they can absorb heat and reflect it back down to the soil surface. Wind also prevents frosts and freezes by breaking up the ascending warm air with the descending cold air. Other factors include slope and humidity. Cold air settles downward and hot air rises, meaning you have a higher risk of frost at the bottom of slopes and valleys. You also have a higher risk when there is less humidity in the air. This is because humidity slows temperature change.
Sometimes I will take temperature readings in my yard at night and compare them to temperatures reported by the news to determine how to prepare for frost advisories and freeze warnings when they are issued. If you’ve recently moved to a new area and aren’t familiar with the weather, it might be a good idea to research average frost dates to predict the likelihood of one occurring.
Once I know a frost is coming, there’s always a chance of “frost injury” or “winter injury” as they call it. Frost injury happens when ice crystals form in plant cells and draw moisture from the plant’s tissue. It essentially dehydrates the plant by disrupting any movement of fluids. A frost-damaged plant may appear shriveled, discolored, or water-soaked.
Proper Plant Selection
I once had a client with a huge retaining wall that he covered with confederate jasmine, a beautiful evergreen with a wonderful smell. Known as Trachelospermum jasminoides, the only problem with this particular plant in this case is that it is a zone 7b plant, meaning it is designed for warmer temperatures and does not do well in North Georgia, which is zone 6b. These zones are determined by the USDA Hardiness Zone Map, which divides North America into 11 planting zones separated by average temperatures in the winter season.
Far away, the plant looks great, but up close, you can see the frost injury. Right now the confederate jasmine is still alive because it is on the warm side of a block wall and surrounded by warm concrete. But soon, cracks in the stems caused by frost will eventually lead to the death of the plant.
Timing
An obvious deterrent to winter injury is plant selection and timing. As long as the ground isn’t frozen, we plant year round but we make sure to use cold tolerant plants in our landscape design as a means of avoiding the issue of frost injury altogether. Summer annuals, succulents, subtropicals, or tender vegetables like tomatoes are plants that might need special attention in the winter, but other than those, most plants don’t necessarily require extra care in cold seasons, especially if you live in the Southeast where the threat of frost or snow is significantly lower.
Frost injury will be less severe if the plant is not already stressed for water. That’s why one of the most important aspects of protecting your garden in the cold, dry months is all about watering. I water my yard only when temperatures are above 40 degrees and I try to do it midday so my soil and roots have time to soak it up before possible freezing at night. I manage my soil irrigation carefully as moist soil absorbs and releases heat more rapidly. Practice good watering. Always check the root ball first to be sure the plant needs it. If it is wet, you do not need to water. Apply water directly to the roots and be strategic about thoroughly wetting them. Shallow watering can be very detrimental to the overall health of your plant.
Pruning
Another practice that can help with the prevention of winter injury is pruning, but only if you have to. Most plants do not need to be pruned unless they have diseased, dead, or broken limbs, limbs that may damage property, or the plant is getting too large for the site. Pruning can create more growth but every cut is an opening for insects, disease, and more frost damage. Injured stems and leaves will continue to trap warmth in the cold months and can later be pruned in the spring. It is almost always best to wait until winter is over to assess the damage. Your plant may drop the dead foliage on its own and generate new growth without your intervention. Once the weather has warmed up, it’s a good idea to fertilize and carefully irrigate frost injured plants because they are also now at a higher risk of drought stress in the summertime.
To cover or not to cover.
The main concern for most Georgia gardeners is when something is getting ready to bloom and a frost is anticipated. Some people frequent the use of tarps, boxes, and other plastic products to cover their plants in extreme temperatures and protect them from moisture. Though these methods are tempting and though I hate watching my flowers get mushy, I have to resist the urge to cover my plants and trust in my process. Ya gotta have faith! As long as I have planted the right plant, properly watered, pruned, and given it a period of dormancy for its roots to grow stronger, I know it will survive and bring me joy next year. A covering does not necessarily have to be a part of its winter protection plan. As with all things, solving the root issue (pun intended) instead of using a band-aid will benefit you more in the long run.
Sources:
http://marinmg.ucanr.edu/Our_Projects/Leaflet/How_to_protect_plants_from_frost/
https://www.almanac.com/how-predict-frost
https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1002.pdf
https://garden.org/nga/zipzone/
