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Now that the growing season is almost over, gardeners can focus their attention inward and beautify interior landscapes with tropical plants that make the cold Colorado winters more bearable. These plants humidify the air and clean it of gaseous pollutants, such as formaldehyde, ammonia and certain chemical solvents. A few even flower virtually nonstop all winter!
Begin by bringing some of your favorite garden plants inside. Plants grown as annuals - geraniums, abutilons and semperflorens begonias - can be grown indoors, as can the plectranthus (Swedish Ivy relatives) and spikes (dracaenas) used in patio pots. If placed in a bright south, east or west window, geraniums, abutilons and begonias will bloom almost all winter.
Geranium leaves will yellow and wither when abruptly placed indoors; this, however, is temporary. To avoid bringing in tobacco budworm, examine plants carefully, discarding any with small holes in the buds. Wash or spray plants thoroughly with water to rinse off any eggs on the buds. Rinse off all traces of garden soil and repot the geraniums in a loose potting mix. This is important because budworms spend the winter as a pupae buried in two to six inches of soil.
Humidity
Success with indoor plants means choosing healthy, pest-free plants and giving them the right amount of humidity, light, water and fertilizer. Colorado's environment is not ideal for houseplants. Most indoor plants are natives of the humid tropics, where humidity levels are 80 to 90 percent or more. Here, indoor humidity levels can be as low as 10 to 30 percent, especially during winter, when heating ducts spew forth dry, warm air. It's no surprise, then, that a succulent such as jade, which is better adapted to lower humidity levels, does well here. If your heart is set on tropicals, you must create a humid environment.
A humidifier is one option. Massing plants together or placing them on trays, lined with pebbles and water is another. The pots must sit on, not in the water. The presence of a lot of plants, particularly large ones, raises humidity levels considerably; Many tropical plants adapt well to humidity levels of 40 to 50 percent, also considered for ideal for human well-being.
Light
When buying a plant, your availability of natural light is the most important consideration. Try to match the plant's light requirements to your location. You might want to begin with a good, illustrated houseplant book. Illustrations are important because many plants are now simply identified as "tropical foliage plant." Identify them so you know their light and other requirements.
Many houseplants are shade plants that do well in reduced light. Flowering plants and variegated plants generally require more light. Tropical plants that grow in full sun outdoors cannot reach their potential indoors unless they receive very high light levels, in a south window, for example. Passionflowers and hibiscus are examples of very high light plants. African violets and their relatives bloom in lower light. Streptocarpella, an African violet relative, blooms almost non-stop at the reduced light levels of a north window. All it wants is a little water, a little fertilizer and an annual haircut.
Most houseplants fall into three basic groups:
High Light Plants
- The equivalent of 4 to 6 hours of sun daily
- Within 2 feet to 6 feet of a south glass, October through March
- Within 2 feet east or west glass, all year
Medium Light Plants (Bright light, but no direct sun)
- Within 2 feet of north glass, April through September
- 2 to 6 feet back from a west or east glass all year
- 2 to 6 feet back from a south glass all year
- Typical office lighting, 12 to 14 hours per day
Low Light Plants
- Within 2 feet of north glass, October through March
- 6 to 10 feet back from a south glass, April through September
Pests and Other Problems
Before you buy an indoor plant, be sure it is healthy. Ask to remove the plant from its pot so you can look for healthy light-colored roots. Some retail outlets won't let you do this, but ask anyway. Look at its leaves. Unnatural leaf distortion, yellowing and leaf drop are bad signs. The former can indicate insect damage, the latter often means underwatering or overwatering.
Often we first notice insects, such as spider mites, mealy bugs and scale, several weeks after buying. They didn't appear out of nowhere, but were there all the time, hiding on lower leaf surfaces or lurking where leaves attach to stems. Or, you may have brought home the insect eggs. For these reasons, isolate new plants so you do not jeopardize the others.
Examine the plant, looking especially on the undersides of leaves, for fluffy white cottony flecks (mealybugs). Look for tiny black or reddish-black specks or for miniscule spiderwebs together with bronzed, mottled leaves. These signs are dead giveaways for spider mites.
Scale insects show up on leaves and branches as raised brown dots. These critters are difficult to get rid of and, in the process of trying, you could injure delicate plants, such as ferns. Use quilted cotton rounds soaked in alcohol to kill mealybugs and scale insects. Spider mites often can be controlled with repeated sprays of water. Shower off leaf undersides, where these pests set up housekeeping. If this doesn't work, try a soap spray formulated for houseplants. Prune out infested areas. If your plant is heavily infested, consider discarding it.
For those who don't want to pollute their indoor environments with pesticides, try a horticultural oil mixed with water. Apply outdoors in the shade. (The sun will burn the foliage.) More than one application may be needed.
Watering
It's quite possible to kill your plants with kindness. Too much water and too much fertilizer probably are the leading causes of indoor plant mortality. Your potting mix needs to dry enough in between waterings, so the roots can take up oxygen. Waterlogged roots begin to rot and cannot supply enough water to the leaves, which then wilt. Don't water a wilting plant until you determine what's wrong. If a plant goes too dry, leaf edges can become dry and brittle. Use your fingers to test soil moisture. If soil clings to your fingers, wait to water.
Fertilizing
Excess fertilizer causes the build up of mineral salts in the potting mix, interfering with plant water uptake. The leaf edge, unable to get sufficient water, may become brown and dry. Don't fertilize newly purchased plants for several months. Usually growers have fertilized them heavily to maximize production. Any more is overkill. When this initial period is past, once a month is fine.
When fertilizing flowering plants, alternate a balanced water-soluble fertilizer labeled 20-20-20 with one specifically formulated to promote flowering (Usually 10-52-10).
Houseplant needs are fairly straightforward: adequate light, adequate humidity, regular watering and feeding, and good control of pests and diseases. If you provide these, your plants will thrive and reward you amply.
Colorado State University Extension offers a booklet, Colorado House Plant Tips, about growing houseplants in Colorado. Published as Bulletin 569A, the booklet is available from the Extension Resource Center, 115 General Services Building, Colorado State University, Fort Collins, Colorado, 80523-4061. You also can phone or fax in your order - Tel: 970-491-6198; Fax: 970-491-2961.
For more information on Gardening, contact your
local Colorado State University Extension office.
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