Protect tender plants during hard freezes

By By Steve Strong / area horticulture extension agent
Jan. 21, 2004
South Mississippi was lucky enough to make it over half way through the winter without a real cold snap, but it finally arrived this week.
Temperatures plummeted to the 20-degree mark in the Meridian vicinity, sending gardeners scurrying to wrap water pipes and cover prized landscape shrubs and fruit trees.
Freeze protection can be crucial when temperatures remain below the mid-20s for extended periods of time, and a simple layer of mulch can sometimes mean the difference between life and death in the root zone. Pine straw, leaf mold, bark chips and even composted sawdust can be used for mulching, and the lighter the material the more that can be applied around the plants.
Four to 6 inches of pine straw is generally enough to protect roots on hardy trees and shrubs, although gardeners with tender perennials like hibiscus and gingers may choose to pile on several feet of mulch for good measure.
Some folks have been known to use wire baskets around planted areas to help hold the mulch in place, and watering over the top to form an ice layer can provide even better insulation against cold air.
The ice trick can be effective as long as the plants are completely dormant with flower buds still closed, as in the case of most fruit trees (once flower buds are open, icing can do more harm than help). Entire shrubs can also be protected with this method, and it is best to cover the plants with several light layers of water to build a thicker ice coat be careful about coating the plants too heavy or they could snap under the weight.
Freeze wrap materials can be found at many building supplies and garden centers, but old bed sheets and blankets may work just as well. The thing to remember with covers is that sunlight causes a heat buildup underneath, so the freeze wrap must be removed promptly each day when the temperature is expected to climb above the freezing mark.
Plastic sheeting also makes suitable mulch, but be aware that plastic does not allow for proper air flow and heat release, and you end up with boil-in-bag plants if you are not careful. Extreme warming of dormant plants can cause the bark to split, and it is a common sight on young trees planted with a southwest exposure that is why you often see white shaded bark wrap placed around the main trunk as a prevention.
Last but not least, outdoor lighting can work in a pinch, and is normally used in combination with some kind of cover to trap the warmth. Incandescent bulbs of 75 to 100 watts are fine, just be sure to use only UL-approved outdoor wiring, and do not place the bulbs in direct contact with plant parts or the cover material.
All methods of freeze protection have a limited amount of effectiveness, and there is little that can be done if the temperature falls to single digits.
If plants should happen to die from frost injury this winter, consider replacing them with better, winter hardy varieties adapted to chilling that sometimes reaches even down to the Gulf Coast.
Visit the MSU Extension Service Web site at www.msucares.com for information on adapted varieties of landscape plants, fruit trees, and vegetables. The local number to call at the Lauderdale County Extension office is 482-9764. You also can e-mail a message to lauderdale@ext.msstate.edu.
On a final note, the best freeze protection for plants is to have adequate amounts of potassium in the soil, which acts as a natural "antifreeze" for the root systems. Now is a great time to have your soil tested for just $6 per pint sample to protect your gardening investment from the harsh environment better known as Mississippi weather.