Window glass was a momentous innovation for indoor horticulture. The process of making large pieces of glass thin enough to allow light through was developed a little more than 300 years ago. Sunlight crucial to raising plants didn't reach indoors until the late 1600s. Today houseplants are used as decorating elements and to form indoor gardens.
One can employ them as architectural accents, focal points and conversation pieces. Plants can be used as living sculpture or can form lush, inviting sitting areas. They are a natural for room dividers, screening, directing traffic and softening hard edges, such as steps and corners.
Houseplants are also therapeutic. Plants in the workplace reportedly foster less absenteeism and higher morale. And at home or at school they can be used to help children learn about nurturing life.
Exceptionally shade-tolerant tropical plants that will thrive on low humidity and indirect light make successful indoor gardens. Decide on your houseplant design just as you would on your landscape. Choose favorite colors and style, how you plan to use the area, and the amount of sun and maintenance requirements. Then it's time to find your plants.
Foliage plants tend to be lower maintenance, but you can also nurture flowering houseplants -- my favorites in the winter -- such as orchid, African violet, cyclamen and gloxinia. Supplement with florist's azaleas and hydrangeas, bulbs and cut flowers.
In Barbara Pleasant's latest book, "Complete Houseplant Survival Manual" (Story Publishing, $24.95), she explains the care of indoor plants and examines, in detail and encyclopedic format, their needs. For anyone who wants a thorough understanding of houseplants, botanically and aesthetically, the information is well organized and very complete. There are hundreds of color photographs and illustrations in its 365 pages.
This manual is broken into an introduction and plant identification guide that includes blooming houseplants, foliage houseplants and houseplant care. There are appendices with glossary, resources, and cross references. Here is a sampling of advice that Pleasant provides about some of my favorite flowering houseplants, and a few tips about interior foliage plants.
* African violet (Saintpaulia hybrids) is an excellent plant to grow on a window sill that receives filtered light. They are best kept indoors year round and can be damaged by over-watering, low temperature or hot sun. Buy plants in bloom for immediate gratification and to know what color you are getting. They will continue to flower with proper light. Keep the growth medium evenly moist, and do not spray the leaves or get them wet. Fertilize every two weeks with a water soluble fertilizer at one-half the recommended rate. Re-pot once a year to freshen soil and plant slightly deeper when transplanting. All have similar needs. Choose by flower color.
* Amaryllis bulb (Hippeastrum species and hybrids) blooms 6 to 8 weeks after planting. Set bulb in a container with a maximum of two inches between bulb and pot. Leave the top third of the bulb exposed to ensure drainage. Water well and keep it at 60 degrees until a shoot appears (about four weeks). Then move it to good light for a few weeks and fertilize with a balanced nutrient (like 9-9-6 Bulb Booster) every 10 days. Flowers can be red, white or pink. Cut the flowering stalks when blossoms fade, and continue to water and feed. In late summer, allow plants to dry gradually. Cut off old leaves. Store at 50 degrees for a minimum of 10 weeks. Re-pot firm, healthy bulbs 6 to 8 weeks before you want flowers.
* Christmas cactus (Schlumbergera hybrids) flowers depend on climate factors -- bright light in summer and fall, combined with days that gradually become shorter and cooler. Move these rain forest natives outside when danger of frost has passed and bring indoors when average night temperatures reach 40 to 50 degrees. Bring them into a cool room that has no light after sunset (the point they should be at now). In early winter, when flower buds form, place pot where you want to see their blooms. They are available in a huge range of colors. Shifting the plant a lot will cause buds and flowers to drop. Keep flowering temperatures about 60 to 65 degrees. Fertilize every two weeks, spring and summer, and monthly in fall and winter. Keep soil lightly and evenly moist during the growing season, less water in winter. Shriveled stems are signs of low water.
* Cyclamen (C. persicum hybrids) should be kept in a cool location -- 60 to 70 degrees -- in a bright window, two hours of sun daily in winter. When foliage withers in late spring, clip leaves and allow to go dormant in a cool dark place for two to three months. Provide barely enough moisture to keep roots from drying. In late summer, return the pot to a bright location. When growth appears, re-pot the plant in fresh soil and resume watering and fertilizing every two weeks at half the recommended strength on label. Soft-pink- to lilac-colored flowers begin to appear again in two to three months.
* Orchids as houseplants often bloom in winter. In 15 pages covering them, Pleasant introduces beginning growers to five of the more than 28,000 orchid species. Generally she recommends that you start with one of the easy-to-grow varieties, such as cattleya, dendrobium or paphiopedilum, and work your way up to a collection. Generally, keep most orchids in brightness without direct sun. They are helped by fluorescent grow lights. Keep their space humid, and learn their temperature requirements. Some like it hot, 75 to 85 degrees, others like 60 to 75 degrees. All orchids tend to like nights 15 to 20 degrees cooler than the day.
* Dracaenas are especially useful where you want an upright form and wish to add a sculptural element with a plant in your interior design. One called corn plant offers thick foliage; "Massangeana" has a golden yellow stripe and can grow six feet tall; Marginata has long pointed, green or red margined leaves; others have white to gold colored variegations. Their canes grow straight or crooked, giving an Asian appearance. The varying heights, lily or tropical grass-looking foliage and woody canes make it a houseplant with lots of interest. Drainage is crucial. Reduce watering a bit in winter, but do not allow soil to dry. Site in temperatures 65 to 75 degrees Fahrenheit, with indirect light only.
* Pothos (Epipremnum aureum) has a cascading or vining habit and is easy to grow. Its variegated, heart-shaped leaf resembles philodendron. The most popular varieties have variegated foliage, usually silvery, white or cream color. High humidity is best. It's tolerant of shade, but allow to dry between watering.
* Spider plant (Chlorophytum comosum) has strap-shaped leaves that do a good job of cleaning the air indoors. Spider plants' long stems produce plantlets from the flowers. There is a variegated hybrid and an all-green variety. Grow it in a hanging basket or a planter where it can mature into a cascading focal point. Takes some sun or shade and is fairly tolerant of the dryness of indoor environments.
* Palms must be used so that you don't have to prune them. They should grow to a size that will fit the space when mature. Kentia palm (Howea fosteriana) has a clean growth habit in medium to low light. A good upright, slow growing palm, it's the perfect touch for an entry or the corner of a large kitchen or bathroom. They perform well being pot bound, love high humidity, need good drainage and should dry between watering.
* Aglaonema (A. commutatum) is commonly used for its silver to white splotched foliage. It is a low-growing, clump-forming tropical that will survive in conditions where you didn't think you could grow a plant, such as on a table in a darker part of a room. It loves room temperature, tolerates shade well, and while growing vigorously, dislikes cold air and won't take pruning, except perhaps a dead leaf here or there. When growth slows in winter, water less.
* Peace lily (Spathiphyllum) is a dependable houseplant that Pleasant lists with blooming houseplants. I consider it more of a foliage plant. It tolerates shade and wet feet and will flower white on scapes above the long lance-shaped leaves. Water frequently. Drainage must be good. It likes to be moist and will wilt at the first sign of dry soil. Indirect light encourages flowering. Keep indoors, out of direct sunlight. Even a few hours burns the leaves.
Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site, www.gardenlerner.com.