Many of our common houseplants are indigenous to the tropics. Well-loved plants such as Ficus benjamina (weeping fig) from India, Streptocarpus section Saintpaulia spp. (African violets) from Africa and Philodendron spp. from South America are easily grown indoors. All houseplants need proper light, moisture, temperature, humidity, nutrients and maintenance.
Many foliage plants grow favorably in subdued light, while certain flowering plants, cacti and succulents require full sun. Sources of light include natural sunlight and artificial illumination from incandescent or fluorescent fixtures.
Plants are killed more often by the common mistake of overwatering than anything else. In general, it is advisable to allow plants to dry out and then water thoroughly, enough to saturate the entire soil ball. Certain plants, such as cacti, prefer to be watered after longer intervals while others, like ferns, will need watering as soon as the soil begins to dry. The great majority of houseplants fall between these two extremes.
The best time of day to water is in the morning, in keeping with the high rate of transpiration. To tell if a plant needs water touch the soil to feel if it is moist or dry. Water most plants from the top until the water comes out of the drainage hole into the saucer beneath. Sometimes plants will take up water in the saucer as well, but never leave them sitting in water for more than one hour. Extremely pot-bound plants are best watered by soaking. This is done by immersing the plant in a bucket of water so several inches of water are above the soil line. The immersed plant then drinks this water for about a half hour and can be removed to a stand to drain.
Some houseplants like considerable warmth; others need cooler growing conditions. In winter, warm temperatures produced by heaters lower the relative humidity indoors and positions close to radiators and other sources of dry heat are particularly distressing to plants. Many houseplants grow better when the nights are cooler than the days, as this imitates natural conditions. A good general rule is to keep the night temperatures 5 to 10 degrees below the day's. Always guard against cold and sudden drafts, which can cause stress and damage. To prevent damage from cold on winter nights, close shades and blinds and protect the area between the glass and plants (with cardboard or styrofoam panels for instance).
In winter, with the excess dryness of heated indoor air, it is advisable to humidify. This is easily accomplished by creating a more humid microclimate by grouping plants together. Additional humidity can be achieved by frequently misting the foliage of most houseplants. However, water on leaves can damage some hairy-leaved plants such as African violets, gloxinias and gynuras. Another excellent method of adding moisture to the air is to stand plants on shallow trays filled with gravel or pebbles that are always kept wet and/or use a humidifier.
The three main elements necessary for healthy plant growth are nitrogen, phosphorus and potassium, which occur naturally in most soils. Nitrogen promotes green foliage and stem growth, phosphorus encourages flowering and root production, and potassium contributes to overall strength and disease resistance. Fertilizers for flowering plants usually contain a higher percentage of phosphorus and potassium and less nitrogen. A fertilizer labeled 10-10-10 is 10% nitrogen, 10% phosphate, and 10% potash. When applying fertilizer remember less is more! Most foliage plants need less fertilizer than flowering plants. Feed foliage plants only during the growing season from March to September.
Healthy plants require regular cleaning, pinching and checking for disease and insect pests. Inspect plants regularly for signs of infestation. Use a damp cloth or place plants in the shower as part of a regular cleaning routine which removes dust and dirt from the foliage and helps discourage disease and pests. Fuzzy-leafed plants such as African violets and gynura are best cleaned with a soft paintbrush. Trimming and pinching encourages plants to become bushier and healthier. Transplant when plants become pot-bound: if plants require enormous amounts of water and show roots coming out of the base they probably need repotting. The most adventitious time to transplant houseplants is in the early spring when they begin to show signs of new growth.