Problem type: Environmental
Name of problem: Low humidity
Plant name(s): Most house plants, especially those of tropical origin
Symptoms / Characteristics:
Younger leaves begin to dry up, beginning at the leaf edges and progressing inward. Lower leaves may turn yellow and fall from the plant. Flowering is inhibited and existing buds shrivel and drop. Open flowers exhibit marginal browning and are very short-lived. Overall growth and vigour are greatly reduced. Plants suffering from low humidity are extremely susceptible to spider mites and may exhibit the characteristic symptoms of injury.
House plants that are of tropical origin thrive in high humidity and often suffer inside the home where there is far less moisture in the air. When humidity of the air is low, the plant loses a tremendous amount of water through the leaf pores and tissues begin to show symptoms of drying. The effects of low humidity are particularly severe during the winter when homes are being heated. Air conditioners will also contribute to low humidity inside the home.
Control / Preventions:
Adding a humidifier to the home is the most effective way to increase the amount of moisture in the air, thus providing comfort to both people and plants. Both portable humidifiers and furnace-mounted humidifiers are available.
There are several less effective but less expensive ways to increase humidity around plants. The easiest method involves simply moving the plants to an area of the house with slightly elevated humidity, such as the kitchen, bathroom or laundry room. Also, keep plants away from heat vents and drafts.
Plants lose water through their leaf pores in a process known as transpiration. Grouping plants together will help create a high humidity microclimate around the plants. Essentially, each plant benefits from its transpiring neighbours.
Place plants on a large tray or saucer containing gravel or pebbles and fill the tray with water. The water will evaporate, raising the humidity in the air around the plant. Make sure that the level of the water does not reach within 1-1.5 cm of the bottom of the pot. If the water is allowed to soak into the pot, the even more dangerous effects of overwatering will result. Pebble trays are most effective when larger surface areas are available for evaporation. Grouping plants together on a single, large pebble tray will be more effective than placing plants individually on smaller pebble trays. A similar technique involves placing water basins amongst the plants. Again, effectiveness is determined by the surface area available for evaporation.
Small or slow-growing plants that require extremely high humidity can be grouped together in a terrarium or glass garden. Water cycling inside the terrarium creates a high moisture microclimate suitable for either tropical or woodland plants. Because temperature is also controlled, the plants inside a terrarium should have similar temperature requirements. A removable lid is required for the occasional release of excess moisture. Never place a terrarium in direct sunlight.
A technique known as double potting can effectively combat low humidity conditions. It involves placing a potted plant (or plants) inside a larger pot lined with damp sphagnum moss. The moss should be kept evenly moist so that continuous evaporation will effectively maintain elevated humidity around the plant.
Although only a short-term treatment, a daily misting with tepid water is a good practice. A fine mist should be used instead of a spray. Sprayers tend to leave large droplets on the leaves that can actually burn the tissue if in direct sunlight. Avoid misting plants with fuzzy or hairy leaves as this can lead to the development of leaf spots.
Humidity levels inside the home may never satisfy the requirements of certain plants. Select house plants that are more tolerant of low humidity such as philodendron, schefflera, snake plant and the bromeliads. Cacti and succulents are suitable selections for extremely dry conditions.