Overwintering Your Plants

Gardening is the #1 leisure time activity in the United States. Hundreds of millions of dollars are spent annually for plants, soils, fertilizer, plant accessories and equipment as we try to beautify the world around us. Countless hours are spent pruning, trimming, potting, watering and generally caring for plants. Many of us improve the quality of our homes and the quality of our lives by planting flowers, shrubs and trees in our landscape, and by bringing plants indoors. Plants also serve an important function by improving our environment. Plants around the outside a home help the environment by cooling the air, providing shade and reducing pollutants. Indoor, plants also improve the environment by reducing pollutants in the air, especially important in newer, tightly built houses.

The secret to success in growing plants is to remember that they are living organisms. Just like people, plants respond to the environment. They are affected by temperature, water, humidity, all the things that humans respond to. A plant is at a disadvantage in that if the growing conditions do not suit it, it can not get up and move to a better place. It can not turn up the heat in the winter, or the air conditioning in the summer. It can not go get a drink of water when it is thirsty. Some people have "green thumbs", others claim they have "brown thumbs". The big difference between the two is the "green thumb" pays attention to details, and provides the proper care for the proper plant in the proper place. The "brown thumb" purchases a discount special and hopes for the best.

Overwintering Houseplants

Plants are a very tough group. They have adapted to environmental conditions over many years, and some type of plant can be found growing in all parts of the world. They are a very diverse group of organisms. Hundreds of thousands of different species have been identified, with hundreds of thousands yet to be discovered. More than 200 different types are commercially produced and used as houseplants. In nature, these plants may be suited to 50 different environments. Problems arise when they are placed under the single environment found in the home.

All plants, whether indoors or out respond to the environment in which they are grown. The ones of main concern are light , temperature and water. Although we talk of them as separate factors, it is important to remember that all environmental factors act together affecting plant growth. Under higher light, plants grow faster. They require warmer temperatures and more water. As light levels decrease, there is less of a demand for water. When grown at low light and warm temperatures, plants tend to get lanky and eventually weaken. For optimum growth, all conditions must be optimum. A change in any environmental condition will change how the plant reacts to the other conditions.

Light usually present the biggest problem to growing plants indoors during the winter. Natural light levels during the winter may be as low as 20% of summer light. The problem is increased when houseplants summer out of doors on a patio or deck and are brought in for the winter. They should be acclimatized slowly to lower light conditions, allowing the plant time to adjust. Rapid change from high to low light will result in leaf drop. Although the plant may produce a new set of leaves, it must use a great deal of stored energy to do so.

For best success, one must match the light conditions of a room to the needs of a plant. Rooms with southern and western exposures have more light than those with northern or eastern exposure. A philodendron or English Ivy will be quite happy under low light, but a spider plant requires much more to continue to grow through the winter.

Temperature is an important factor for successfully growing plants indoors during the winter. Most people set their thermostats to a level comfortable to them, and don’t really consider their plants. In general, houses are much to warm for satisfactory plant maintenance. Under low winter light conditions, most house plants will respond to temperatures between 60 and 70F. As the temperature approaches 80F, plants will rapidly decline.

Cold temperatures can be a factor during the winter. Plants on a sunny window sill may freeze at night if too close to the glass. Cold drafts from opening doors can affect sensitive plants.

Water is probably the biggest threat to indoor plants. They get watered too much or too little. A question I often get is "when is the best time to water my plants?" The answer is simple, but never well received– when they need it. All plants are unique and have different watering requirements. Ten Boston ferns could be placed side by side, and all have slightly different water needs. "Green thumbs" water each plant individually, when it needs it, not because today is Tuesday, or it might dry by tomorrow. The best way to tell if a plant needs water is to stick your finger into the soil about 1-2 inches. If the soil is dry at that level, it is time to water the plant. If it is not dry, wait until later.

Waterers tend to break out into 2 groups. The first flood their plants and then let the plants sit in water that collects in the trays under them for hours or days. The other group tends to continue with the water restrictions imposed during the summer and add water very sparingly. The best way to water is to wait until the plant is dry, then thoroughly soak the plant until water runs out of the drainage holes. After the pot has had time to drain (15-20 minutes) remove the excess water from the tray.

Many indoor gardeners worry about fertilizing plants during the winter. In many cases, this is not necessary because plant growth is much slower during the winter. If you feel your plants absolutely must have fertilizer during the winter months, use a liquid formulation at about half the recommended strength. Always used a balanced fertilizer (the 3 numbers on the package should be very close to each other) and use a fertilizer with a high source of nitrate nitrogen. (The amount of nitrate is always listed on the package. Other sources of nitrogen at high levels can be toxic to plants during the winter.

Humidity may prove to be a concern, especially in houses that use forced air heat. This type of heat is very dry and can damage plants. Humidity can be increased around plants by placing them in groups or by placing the pot on a water-filled pan of gravel. The gravel keeps the roots from sitting in water, and as the water evaporates, the humidity rises around the plant. Misting is claimed to be helpful, but is not nearly as effective as the previous two methods.

Holiday Plants

Holiday plants such as poinsettias, bulbs and cut flowers are often brought into the house this time of year. Before purchasing plants, inspect them for diseases and insects which may spread to other plants already in the house. Make sure they are properly packaged for the trip home. Poinsettias are sensitive to temperatures below 50 F and quality can be reduced by walking from the store to the car on a cold day.

Once home, holiday plants are like other plants. In general, potted plants will require bright, indirect light, temperature between 60-70 F and water as needed. Poinsettias and other potted plants won’t require fertilization during their decorative life.

Some important considerations:

Don’t place in direct sun

Don’t place under heating vents or in front of opening doors

Don’t place on a televison, radiator or other heat source

Do poke a hole in the foil wrapping to allow water to drain

Do check for water daily

Do recut stems of cut flowers at least every other day

Do use a preservative with cut flowers

Outdoor Plants

Outdoor landscape plants are of special concern because of the cost involved. To ensure winter survival, again, attention to detail is important. This begins before the plant is placed in the landscape. Plants well-suited for their environment will survive and thrive during the summer and build up reserves for the winter. A plant in poor condition at the start of winter is much less likely to survive than a plant in good condition.

In an established landscape water is the most important factor to consider, especially with broad leafed evergreens. As the outside temperature lowers in the fall, plant growth slows and plants eventually appear to be dormant. Many are, but others maintain a low level of growth through the winter. Roots continue to grow as long as soil temperature is above 40-45F. Last winter, soil never got lower than 41F in Fort Valley. If there is not sufficient rain, plants must be watered through the winter to keep them from drying out.

Many questions arise concerning pruning and when it should be done. Any broken branches should be pruned immediately regardless of season to prevent further damage. Other than for damage, plants should not be pruned in the fall. This will encourage new growth that will not have time to harden off before winter. Most plants can be pruned in late February-early March, just before spring growth begins. An exception to this is spring-flowering plants. They should be pruned after blooming to prevent cutting off the flower buds.

The best chance for success in overwintering landscape plants is to have a good plant to begin with. One that grows vigorously during the summer and is suited for the climate will withstand winter conditions much better than one that is barely surviving the summer.