Home-garden expert Jim Johnson of the University of Tennessee Agricultural Extension Service offers tips on avoiding common houseplant mistakes. One of the easiest ways to kill a houseplant is to purchase it at the wrong time of year. Many indoor plants are native to the warm tropics and may go into a state of shock if the temperature fluctuates more than a few degrees. Tropical plants are raised in warm greenhouses and could be killed if subjected to cold temperatures for more than a few minutes. The opposite is also true: a houseplant can be killed if it sits in a hot car. Never pot a houseplant in garden soil. Instead, use a fast-draining potting mix formulated for indoor plants. The humidity in an average home is too low for most tropical plants. Exceptions include cacti and succulents, which do well in low-humidity environments. Most ferns and orchids should be misted daily to provide the humidity they need. You can raise the humidity level around your plants by placing a humidity tray under each plant. Make a simple humidity tray by putting gravel in the saucer beneath the plant. The humidity tray will catch water after it has passed though the soil and allow it to evaporate back up into the foliage. Avoid setting plants near heating and air-conditioning vents or exterior doors. Houseplants suffer if they receive too much or too little light. Direct sun from a south-facing window is too intense for many indoor plants; direct sun from a north-facing window during the winter may not provide enough light. Avoid placing plants close to windows--temperatures may fluctuate from very cold to very hot and damage plants. Light is measured in foot candles, the amount of light emitted by one candle at a distance of 1'. Low-light plants require at least 25 foot candles of light, although they prefer 75 to 200, equivalent to the amount of light shining through a north-facing window. Medium-light plants require 75 to 100 foot candles and prefer 200 to 500, the equivalent of an east- or west-facing window. Plants with high light requirements need at least 200 foot candles, preferring 500 or more, the amount provided by a south-facing window. Plants with very high light requirements need at least 2,000 foot candles of light. To provide that amount, you'll need to grow plants under fluorescent lights. If all your windows face north, stick with low-light plants. If they face east or west, choose medium-light plants. To provide ideal growing conditions, place indoor plants outside from late spring to early fall, but make sure to bring them in if the temperature rises quickly and to keep them out of direct sun.
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