Well that last cold snap of winter is headed our way. When these late freezes threaten, we get a lot of calls in the county offices on how to protect plants in the landscape.
As with many other things the first step in preventing repeated problems with cold weather damage is to select plants that are adapted to grow in our area. For example, most oak trees do well in our area while banana trees are often pounded by freeze events. We are all aware of the old saying "an ounce of prevention is worth a pound of cure". Check your plant's USDA plant hardiness zone before purchasing a plant for your landscape. Check the plant hardiness zone of your plant by consulting the nursery or garden center supplier, a good gardening book, or by contacting the county Extension office. Most of Alabama falls either in Zones 7 or 8.
You can also help to prevent cold weather damage by avoiding planting sensitive plants in low lying areas of your landscape. Remember that cold air tends to settle into low areas so you might see the plants in low lying areas severely damaged by a freeze while the same species growing in higher or more protected areas suffer no damage at all.
One of the best ways to provide protection for our prized landscape plants is to provide them with cover. While I do understand that it is impossible for us to cover an entire landscape or garden, providing cover works very well for specimen plants, plants grown in containers, or small bed areas.
There are several materials that can be used for covering plants. Sheets, light blankets, or even excess burlap sacks can work very effectively.
Covering your plants with such materials allows the plant to capture radiant heat from the soil, so it is important that when you cover plants make sure your cover contacts the soil's surface on all sides of the plant. Many people use plastic to cover the plants. While plastic can work, I personally am not fond of using plastic. If the plastic touches the plant foliage, you will lose its insulation effect, and it can also cause scorching of the plant when the sun comes up the next day. Thus it is very important to never let any material that you use to cover your plants to actually contact the foliage of the plant. It defeats the whole purpose of covering them in the first place.
Keep in mind that if you cover your plants the warming effect comes not necessarily from the covering itself but rather the covering helps to catch and hold heat released from the soil. It is important to remember that your cover should have ground to ground contact on all sides of the plant in order to be of the most benefit.
Be sure to remove all plant coverings regardless of the material the next morning to allow for light and airflow and prevent overheating from the sun.
If you have small tender individual plants you can even use such things as old milk jugs, jars, or even large paper cups to provide protection.
Another way to offer your plants some freeze protection especially before an anticipated freeze event is to thoroughly water them the night before. The water will actually make the air temperature around your plants a little bit warmer and it will also allow the plant to replace moisture lost through transpiration. Damp verses dry soil can actually mean the difference between saving your plants or having them suffer severe cold weather damage during a freeze event.
Mulching will also help by creating a barrier between the outside air and the root system of your plant. The mulch holds soil moisture thus helping to insulate the plant roots. While mulch may not prevent frost damage to blooms or above ground structures it will definitely help to protect the plant's most important structure…its root system.
Potted or containerized plants are the most susceptible to cold damage of anything in our landscape because their root systems are less protected and because pots and containers usually drain so well they are usually drier as well. Newly established trees, shrubs, flowers, and even turfgrass are much more likely to be severely damaged by cold weather; while established woody ornamental plants should come through our winters without major problems.
Relocate potted plants to a protected location such as a basement, garage, or storage building when there is a chance of freezing weather.
Wrapping the container in burlap or even that extra bubble wrap that you can never figure out what to do with will help add extra protection if the plant cannot be moved.
Our last frost date for much of central and certaily for north Alabama is April 15. Hopefully, we're seeing the last of winter in 2009.
Source: Danny Cain, Walker County Extension Coordinator
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