Stephen Nameth
Nancy Taylor
Jim Chatfield
A great variety of plants are used indoors to enhance the beauty and soften the harshness of our working and living environments. There are many environments that we classify as "indoor." Indoor environments are not generally thought of as "natural" environments. Nevertheless, it is possible to maintain the health of plants in these environments for many months or years.
Different kinds of plants require specific environmental and care needs to keep them healthy. Thus, an important aspect of managing the health of indoor plants is selecting the right plant for the indoor environment you have. Also, plants should be selected according to the care programs you are willing to undertake. Always buy conditioned or acclimated plants from reputable sources.
Although the care of plants can sometimes be a matter of knowing the specific needs of the plant types selected, health management is also a matter of recognizing the general needs of plants and developing care programs that provide generally well-balanced environments. The plant will react to all of the elements of its environment simultaneously from day to day. When one element becomes imbalanced it may trigger a stress. Uncorrected stress will soon lead to poor plant health.
An imbalanced or non-optimal element of the environment may be "corrected" by direct action or, indirectly, by adjusting into balance the other elements of the environment that are simultaneously affecting the plant. For instance, as the season of the year changes from summer to winter, the amount of light available to the plant may dramatically decrease. You could add supplemental light or move the plant closer to the window. You could also maintain plant health by decreasing the rate of fertilization and watering to bring these environmental elements into better balance with the lower light situation.
To increase your plant health management skills, learn to recognize the elements of the environment that can commonly become imbalanced. Most of them are discussed in the following paragraphs.
The quality of light, as well as the quantity of light, greatly affects the health of indoor plants. The use of "grow" lights can solve light quality problems, but may not provide sufficient quantity. Low light levels (less than 50 footcandles of daylight or 100 footcandles of fluorescent or incandescent light) can be satisfactory for the health maintenance of many plants if fertilizers are used sparingly and the plants are properly conditioned or acclimated prior to being placed in these environments. Condition plants by placing them at 250-300 footcandles of light for several weeks prior to final placement. Foliage one foot away from a reflectorized 40W fluorescent lamp will be in about this much light. Too much light (4 or more hours of direct sunlight on the foliage) can cause problems if fertilization rates or watering frequencies are not properly balanced.
Most indoor plants prefer day temperatures between 60 degrees and 70 degrees F. Rapid temperature fluctuations (window drafts, exposure to air from heat registers) as well as exposure to air under 45 degrees F will result in poor plant health. Remember that sunlight directly on leaves can greatly increase leaf temperature.
Air under 30% relative humidity that is blowing over foliage for many hours each day is very stressful to most plants. In most indoor environments, winter air is far drier than summer air. Using room humidifiers, redirecting air currents, or growing plants above trays of water (gravel beds) may help.
Containers should have drainage holes that are large and numerous. Watch that the holes do not become plugged with roots or compacted soil. Use a saucer to catch water that drains through, but do not allow plants to sit in the water. Do not water plants via the saucer. If you wish to use an undrained decorative container, use a smaller, correctly drained container within it (double potting).
Soil or planting media must be well aerated, yet retain sufficient moisture to maintain plant health between waterings. Many inexpensive packaged growing media (most notably, those containing black or "Michigan" peat) are too poorly aerated for use. Also, they may be inconsistent from package to package as far as nutrients, soluble salts, pH, and presence of root rotting fungi are concerned. Media used by local commercial greenhouse growers are generally satisfactory for maintaining healthy indoor plants. Homemade soils containing more than 20% garden soil are generally unsatisfactory.
If soils are properly constituted, weekly thorough soakings are usually sufficient for plants in most indoor environments. However, do not depend solely on the calendar to schedule watering. Inspect the soil-under the surface, 2 to 6 inches-to determine watering needs. Each watering must thoroughly wet the soil and the entire root mass. Use of tepid water (60 degrees to 80 degrees F) is beneficial. Excess water must drain out of the container. If soils have dried excessively, they may be difficult to rewet. Water may run freely through or around the root mass. Watch for this and soak such soil masses in water for several hours until they are properly rewetted. Pot-bound plants and large plants in small pots will need watering more frequently.
A complete soluble fertilizer containing nitrogen, phosphorus, and potassium (NPK) should be used. The amount to give to the plant will be directly related to the quantity of light being received by the plant. Many fertilizer levels are written for plants in abundantly lighted locations such as bay windows or greenhouses. As a result, many indoor plants are overfertilized. Always dissolve the fertilizer in tepid water and drench the solution through the root mass.
These pests can be problems, especially when "indoor" plants are put outside for the summer and then brought back into the house. Learn to recognize insect and mite pests and take appropriate action to control them before their populations reach high levels. Follow all instructions on pesticide labels.
Many indoor plants are susceptible to bacterial and fungal leaf spots and blights, fungal root rots, virus diseases, and nematode diseases. However, these diseases will rarely be a problem indoors if proper plant health management practices are being carried out. The dry atmosphere of most indoor environments and lack of wet foliage prevents foliar diseases from developing. Overwatering can lead to fungal root rot. Powdery mildew may be a problem on plants subjected to cold drafts. If you suspect infectious disease, remove diseased portions of the plant, and attempt to correct environmental stresses. For plants of high value submit a diseased portion of the plant or the entire plant to a plant disease clinic for further investigation. Specific remedies can be prescribed at that time.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868