In the Garden:
Northern & Central Midwest
January, 2014
Regional Report

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The pot of this tropical hibiscus is set on a bed of shells filled to half their depth with water. As the water evaporates it raises the humidity around the plant. A bed of pebbles would work just as well.

Keeping Houseplants Humid and Happy

The heat's been on in most of our houses for a few months now. Is your skin feeling prickly and crackly dry yet? You can bet that if you feel that way, your plants do also. We can run for the body emollients, but plants have to rely on our providing extra humidity for them. If we don't give them the additional moisture, they let us know by browning tips and margins, spider mite outbreaks, and generally looking poorly.

It may not seem like a critical issue to deal with, since it's one that will correct itself come spring when the air has more natural moisture and the dry heat from the furnace is more sporadic. But a plant under any kind of stress is just waiting for trouble. Stress can start a cycle of problems that will take all kinds of drastic measures to correct.

What is Humidity?
Humidity is simply the percentage of water in the air. Tropical and subtropical plants (that is, most houseplants) are native to environments with about 80 percent humidity. Most homes fall within the range of 35-65 percent humidity, sometimes falling below 20 percent in the winter, so you can see the problem.

Luckily, many plants are adaptable regarding the amount of humidity they'll tolerate. A house would be uncomfortable at 80 percent humidity, and furnishings and people would start to mildew. If you can keep your humidity from dropping below the 40 percent range, however, most plants will be okay. Avoid buying plants that require extreme humidity unless you plan to grow them in a terrarium.

Create a Microclimate
It's possible to create a humid microclimate immediately around plants. To keep humidity high, you must not only put more water into the air, but also reduce the air circulation that evaporates water from around the plant. Low humidity problems are intensified if the soil is allowed to dry out, if the plant is in a draft, or if it is flooded with unfiltered sunlight.

Some of the most successful ways to raise humidity are to group plants in order to reduce the air circulation inside the grouping, to raise the pot on a bed of wet pebbles, or to double pot a plant, filling the void between the pots with dampened sphagnum or Spanish moss. And of course, an enclosed terrarium creates its own very humid micro-climate.

Humidifying the House
Managing the humidity in an entire house can be done with a humidifier installed directly on your furnace. This theoretically lets you raise or lower the humidity in the entire house by use of a humidistat. However, even with a system such as this, the humidity may not remain high in all areas.

Hand misting or wetting foliage is a common recommendation for humidity-loving plants, but in reality this puts more moisture into the air only temporarily. If the rest of the room is dry, that moisture will evaporate quickly. You would have to mist every few hours for it to be effective. Besides, wetting the leaves of some plants may invite disease problems.

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