Light, temperature and humidity are the most important factors for houseplant health. Many plants typically grown as houseplants are native to the tropics where environmental conditions are much different from those of a Colorado home. To improve their chances for survival as a houseplant, it may be necessary to provide supplemental humidity or light or to place the plant in a cooler or warmer area of the home.
Although houseplants tolerate temperatures that are slightly lower or higher than ideal, less than optimal environmental factors affect growth and quality. The temperature preferences of indoor plants are categorized as cool, intermediate or warm. Cool is 40 to 50° Fahrenheit, intermediate is 60 to 75° F, and warm is greater than 75° F.
Humidity, the level of moisture in the air, affects a plant’s need for water and its health. Plants routinely move water and nutrients from their roots to the stems and leaves using a process called transpiration. When the water reaches the leaves it is released into the atmosphere through tiny openings. High humidity slows this water loss. Plants grown indoors with low humidity or in a draft lose more water through transpiration, so their root systems require more water.
During colder months, heating systems circulate dry, warm air throughout the house and in summer, air conditioning systems circulate dry, cool air. Both of these conditions often create an environment that has less than 10 percent humidity, well below the 70 to 90 percent relative humidity levels found in the native climates of most tropical plants. In addition, plants located near heating or cooling vents are subject to increased air movement that increases transpiration. Many develop leaf spots or brown tips as a result of the lack of humidity.
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 group several plants together on a tray filled with gravel and water. The evaporating water provides the humidity the plants need. The bottoms of the containers should stand above the water so the soil will not become water-logged and cause root damage. Using humidification devices around the tropical plants will also help.
In contrast, many cacti and succulents native to arid, desert conditions adapt well to the low humidity conditions in our homes and are great candidates for houseplants.