November 1, 2007, Article

by David Rodriguez

The month of October and early November is the time to consider protecting your plants for the upcoming winter. Traditionally, here in San Antonio and the surrounding area we have had frosts as early as October 31st. Normally, the first frost date is around November 15th. As a result of past winters, such as 1983 and 1985, we should all be more alert to the potential realities that lie ahead. DO NOT GET COMPLACENT! We have become really spoiled these past few years with our mild winters that average about six frost days in a season. IT WILL GET COLD AGAIN ONE DAY! Hopefully all of us and our plants will be prepared.

In dealing effectively with San Antonio area winters, a basic fact should be taken into account, being there is NO such thing as a typical winter. Unpredictability is the password for the cold months. It is not unheard of for temperatures to drop as much as 40 in less than a 24 hour time span. In spite of the variability, certain patterns do exist and they are helpful in establishing a plan of action to counteract potential problems. Some of these are:

1. Cold weather is usually accompanied by strong winds. Protecting plants from these breezes are very important.
2. The winds are usually very dry, resulting in extremely low humidity, thus causing plants to dry out.
3. Frost and freezing temperatures are usually of short duration, usually only overnight. However, several days of continuous freezing temperatures have occurred in the past.
4. The temperature rarely falls below 15 F in most of the state, but can go much lower.
5. Always be prepared for the potential of widely fluctuating temperatures. It is not too uncommon for an afternoon of 80 plus degree weather to be followed by freezing temperatures a few hours later. This is the greatest single factor contributing to winter plant injury. The frequent warm weather does not allow the plants to become completely dormant.

Taking all these factors into consideration, a few precautions can be taken to minimize the chances for winter injury to your landscape. Some step-by-step procedures to follow include:

Winterizing Container and Basket Plants

1. Container grown plants and baskets are more susceptible to cold damage because their roots are exposed to the extremes. A hardy plant growing in the ground may not be as hardy in a container or basket.
2. Move all containers and baskets out of windy exposures, especially the north wind. If possible, locate areas with some type of overhead cover. Covered patios, eaves of the house, under trees, etc., all help to retain heat. Plants that are extra hardy, such as Dwarf Yaupon holly, Dwarf Burford holly, aspidistra (cast-iron plant), and nandina do not need to be moved, except in the case of prolonged, severe freeze.
3. Tender and tropical plants should be moved into a greenhouse, or other suitable protected areas. If your house has adequate light and other conditions favorable to plant survival, your house will make a good winter storage area. If conditions are unsuitable, or space is a limiting factor, place your containers and baskets near the garage door or a similar area where they can be quickly and easily moved inside during freezing weather.

Winterizing Your Greenhouse

1. Check that the structure is airtight. Special attention should be given to doors, windows, and areas where the structure comes in contact with the ground.
2. Make provisions to have heating equipment checked. Use some sort of alternative for heating.
3. Be sure all water pipes and connections are protected from freezing.
4. If at all possible, the location of the greenhouse should be on the south side of the house, and attached to a window or other opening to the inside. This helps to heat the greenhouse at night, and during the day, the greenhouse will act as a solar collector, helping to heat your home.
5. Any type of shading material should be removed until spring.
6. If your structure is covered with polyethylene plastic, use two layers, if possible with at least one inch of air space in between. This can render your greenhouse up to 50 % more heat efficient.
7. Flooring materials of stone, gravel, brick, or rock will help store heat. Soak floor frequently with water.
8. If no heat is available, a sprinkler left running in the greenhouse during freezing weather will release heat and sometimes prevent plant damage. This should only be used as a last ditch attempt.
9. Trim any overgrown or unsightly plants before moving the plants inside. Use trimmings for cuttings or place them in the compost pile.
10. If need be, spray plants for insects with Safer Soap. Consider applying Di-Syston systemic insect granules every 30 days as a preventive. Also, fertilize plants with Osmocote 14-14-14 time released granules.

Winterizing Outdoor Landscape Plants

1. When developing your overall landscape plan, tender plants such as bananas, gingers, elephant ears, cannas, etc., should be planted in the landscape in such a manner as to not to be visible after their frost damage portions are trimmed. Good locations include: planted within and behind evergreen shrubs, with evergreen ground covers, behind hedges, fences, and walls.
2. Before freezing temperatures occur, water everything thoroughly. Water displaces the air in the soil interspaces and is much slower to cool than air. Moist ground stays warmer than dry ground.
3. Wash any frost off of foliage before the sunlight strikes it. This minimizes damage.
4. For light frosts and freezes, sprinklers can be left on. Usually, the water temperature does not fall below 50 F. With temperatures above 26 F., a sprinkler left on will maintain above freezing temperatures. DO NOT, I REPEAT, DO NOT use this method in low temperatures or during prolonged freezes. Ice collects on plants and causes more damage.
5. Very special plants can be protected by building protective frames or coverings. This can be expensive and time consuming, and should only be done with plants of sentimental “value.”
6. Plants, especially young palms and bananas, attain more hardiness with size and age. Therefore, the smaller plants can be wrapped with burlap, blankets, newspapers, or similar suitable materials, if unusual, extreme conditions prevail.
7. Covering or wrapping plants with plastic films can be more harmful than the cold. Used alone, plastic causes wide temperature fluctuations from day to night. Plastic, used as wrapping, holds very little heat at night, but is extremely hot during sunny weather. Use plastic film ONLY in conjunction with other wrapping materials. For best results, remove the plastic film on sunny days and when the temperature is above freezing. Plastic film is excellent for covering greenhouses, protecting frames, and for making man-made wind screens.
8. In the fall, don’t use a fertilizer that contains high, quick-release nitrogen. Use as little nitrogen as possible, because it will cause new, tender growth to occur. High phosphorus and potassium fertilizers will help to thicken cell walls and stimulate more sugar and carbohydrate production within the plant cell walls. This fortifies and protects the plant, somewhat like antifreeze does in your car radiator. Consider, using a 6-2-4 or 4-2-3 analysis when feeding your landscape shrubs and trees in the fall season. And please…never fertilize your landscape too late in the season.

Remember, Learn and Have Fun!

David Rodriguez is the County Extension Agent-Horticulture for Bexar County. He represents Texas Cooperative Extension with the Texas A&M University System. To get questions like these answered, call the Bexar County Master Gardeners Hotline at (210) 467-6575, e-mail questions to mg-bexar@tamu.edu, or visit our County Extension website at: http://bexar-tx.tamu.edu, click under Horticulture and Gardening.

Special Note: Listen to a live broadcast of the Garden Show with David Rodriguez and Bill Rohde on WOAI 1200 AM every Saturday morning, between 8:00 and 11:00 a.m., call in your gardening questions at (210-737-1200 or 1-800-383-9624). Check it out!