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Larry Sagers
The hibiscus needs high levels of both light and humidity.

Last week, we discussed the factors you need to pay attention to inside the greenhouse to grow plants successfully. The same applies to growing plants in your home.

To review, plants need warmth, light, water, mineral nutrition, air and space. Inside your home, the same needs are critical.

If you're comfortable with the temperature in your home, then it's likely your plants are comfortable, too. There are exceptions, however. African violets prefer warmer temperatures than most of us like, and a few plants, such as flowering bulbs and cyclamens, want it cooler than what we enjoy. In addition, plants don't like drafts or hot, dry air any better than we do.

Light is the most difficult issue to deal with when growing plants indoors. It is tough enough to get light to plants inside a greenhouse, but in a home the problem multiplies exponentially. Even near a window, light levels are critically restricted and most plants suffer from a lack of light.

Solving the problem isn't easy. While windows let in the light, the temperature near windows can get frosty on cold winter nights, meaning it's way too cold for some tropical plants that prefer temperatures above 50 degrees.

Supplemental lighting is difficult. Ordinary lighting is of little value in promoting plant growth, and most people don't want huge, high-intensity lights inside their homes.

The best solution is to select plants that are tolerant of low light and other conditions. Most are tropical plants that thrive in the lower levels of rain forests and similar environments. These plants will tolerate light levels in a home if you pay attention to their other needs.

Plants growing under low-light conditions do not need as much water or fertilizer because they don't grow much. Pay particular attention to these, as excessive amounts of either will cause serious problems or kill your interior plants.

In a greenhouse, people can water freely with a hose or watering can. The water drains through the pots and runs onto the greenhouse floor. Inside a home, many people put saucers under the pots or put the plants inside decorative pots with little or no drainage.

All living cells must burn food for energy. To do this, they must have access to air, which contains oxygen. If a plant's roots are submerged in water, the air supply is cut off and the plant will eventually die.

Make certain the soil drains and the plants never sit in water. Select quality growing mixes with excellent drainage. Mixes that are mostly bark or other non-decomposed organic matter do not grow healthy plants.

The amount of water in the soil isn't the only concern. With interior plants, the water in the air — or the humidity — is also critical. Forced air heating dries the air so that your home has roughly the same humidity as the Sahara Desert.

To help offset this, group plants so humidity from one helps the others. Put the plants on leak-proof trays filled with small rocks. Add water so it is 1/2 inch below the top of the rocks. Water evaporating from the rocks will increase the humidity around the plants. Small humidifiers also help.

Fertilizers are often overemphasized when growing interior plants. They are often viewed as medicines for sick plants, but they only provide nutrients to help healthy plants manufacture food. Doctoring sick plants by overfertilizing is usually fatal. Never fertilize plants unless they have adequate light, warmth, water and drainage.

Use a complete fertilizer with micronutrients added. There are many good brands on the market, including liquid and dry forms. Some are slow release, so they need to be added only infrequently. If you are not attentive to your plants, they are a good choice.

Don't fall for products that make outlandish claims. Plants make their own vitamins and they use 17 nutrients, so adding 50 or 60 different kinds is useless. Follow the manufacturer's directions; remember, all fertilizers are salts, and too much will burn your plants.

The final factor is space. If you get too good at growing plants indoors, you will have to take the only logical solution. Build a greenhouse and move them into it.

Larry A. Sagers is the horticulture specialist, Utah State University Extension at Thanksgiving Point.