By Roberta Tolan
Houseplants are a great way to add beauty to your home during the long winter months, but the indoor environment in Colorado can be harsh for many plants and they may require special considerations to thrive. The most important factors for plant growth are light, temperature, humidity and water.
Light is needed to produce carbohydrates or food energy for plants. As a rule of thumb, the more light a plant receives, the more carbohydrates are produced and these carbohydrates are stored for use during low-light periods.
Plants have differing requirements for light intensity. Some perform best under high light levels, while other plants prefer lower levels.
High light intensity occurs within 2 feet of south-facing windows from October through March and within 2 feet of east or west-facing windows all year. These locations have at least four to six hours of daily sun.
Medium light occurs within two feet of north-facing glass from April through September and 2 to 6 feet back or 1 foot to the side of an east or west-facing window. Typically, 10 to 14 hours per day of fluorescent lighting is considered medium light.
Low light is found within 2 feet of north-facing glass from October through March and 2 to 6 feet back from April through September.
By moving plants to appropriate locations within the home, any number of light intensities can be achieved.
Proper temperature is important for growing plants successfully indoors and, although plants tolerate temperatures that are slightly lower or higher than ideal, it does affect growth and quality. The temperature preferences of indoor plants are categorized as cool, intermediate and warm. Cool is 40 to 50 degrees F, intermediate is 60-75 degrees and warm is greater than 75 degrees. Avoid placing plants so that foliage is touching glass, as cold and hot temperatures can be damaging.
Humidity, the level of moisture in the air, can affect a plant’s need for water. Plants use a process called transpiration to release water into the atmosphere through tiny openings in their leaves. High humidity slows this water loss. Plants grown indoors with low humidity lose more water through transpiration, so their root systems require more water.
During colder months, heating systems common in Colorado circulate dry, warm air throughout the house. This creates an environment that often has less than 10 percent humidity, which is a drastic reduction from the 70 to 90 percent relative humidity levels found in the native climates of most tropical plants. Misting plants may help alleviate this condition, however, it must be done frequently to be effective and it may promote some foliar diseases. A better solution is to place several plants together on a tray filled with gravel. Filling the tray with water provides the humidity many plants need. But, make sure the bottom of the container does not stand in water, because the soil will become water-logged and cause root damage.
The amount of water a plant requires and uses depends on several factors including plant species and structure, environmental conditions such as light, temperature and humidity, cultural conditions of the soil and the type of container used. There are several ways to determine when a plant needs water. Although some plants prefer their root system to become slightly dry before their next watering, it’s best to feel the soil on a regular basis and water before any wilting is visible. Other plants require even moisture and do not tolerate dry roots. These plants should be watered when the top layer of soil begins to feel dry.
When watering your plants, be sure to completely cover the surface of the soil with water so it does not simply drain down between the potting soil and the side of the pot. Plants do not tolerate waterlogged soil conditions, so don’t allow them to stand in water. Plants should be placed in saucers or trays to prevent water damage to floors and furniture. Apply just enough water to fill the tray and discard any water that collects in the tray.
Choosing the proper container is very important and that can vary by plant type. For example, succulents may do better in unglazed clay containers, while moisture-loving plants, like Boston fern, may do better in plastic containers. Glazed clay, wire with peat moss and wooden containers also are available. Avoid treated wood containers because they may affect plant growth and viability.
Select containers that have drainage holes or place a layer of gravel or broken pot shards in the bottom of the pot. Decorative containers often do not have drainage holes, so it may be necessary to double-pot your plant. When double potting, put a small amount of gravel in the bottom of the decorative container and place the clay or plastic container inside. Porous ceramic pots allow more air to reach plant roots than plastic but can dry out more quickly. When using tall, narrow pots, use a finer-textured soil to maintain even moisture and remember, larger pots require less frequent watering.
When you purchase a plant, purchase a container that is slightly larger than the one the plant comes in. If the new pot is more than two inches in diameter larger than the previous pot, the plant will not respond well and the potential for root rot may occur. When using an existing pot, clean it out by applying a solution of 20 percent bleach mixed with water. Then rinse thoroughly with plain water to avoid transferring pathogens and insects.
For more information on the proper care of houseplants or to find information on the care of specific houseplant species, go to Plantalk Colorado at www.planttalk.org. For information on managing the diseases and insects on houseplants, go to www.ext.colostate.edu and download Fact Sheet No. 5.595.