PLANT SELECTION AND MANAGEMENT
Consistent success with indoor plants is most likely to be achieved by:
The most important practice in interiorscaping is the selection of plants matched correctly with the environmental characteristics of the planting site. Plants differ significantly in their light needs, sensitivity to temperature, and ease of maintenance.
Light is probably the most important environmental condition, and plants should be placed and grouped according to their need for light. Plants grown under correct light conditions are vigorous, compact, and bushy. Color is vibrant, leaves are normal in size, stems are sturdy, and flowering is promoted.
Light helps balance food production (photosynthesis) and food consumption (respiration) by the plant. The rate at which plants make their own food is determined essentially by the quantity and duration of available light. The higher the light level, the greater the supply of food. The rate of food consumption is basically determined by temperature. The warmer the temperature, the greater the demand for food. Therefore, in interiorscapes, the low light and warm temperatures create a high demand for food, but a slow rate of production.
Plants grown at a light intensity below their optimum will have smaller leaves and less vivid color. They often grow more open and leggy, and pruning may be necessary for compact form. They need to be kept drier than those in bright light and fertilized less frequently. A plant that receives significantly less than its required amount of light may survive for several months to a year, while gradually deteriorating in appearance and vigor. A wide variety of light meters is available for measuring light intensities in indoor environments. Light meters can eliminate much of the guesswork in selecting plants that are adapted to light levels in a given location.
Plants for low, medium, and high light locations are listed in Table 1. In general, there are three categories of light intensity for interior plants. These are described in footcandles (fc). A footcandle is the amount of light cast by a candle on a white surface at a distance of one foot. Ranges for low, medium, and high light intensity overlap and vary in different references:
Leaf structure in plants produced under near or full sunlight is different from leaf structure in plants produced under low light. Leaves of plants in high light conditions are structured to avoid some of the strong light intensity. These small, thick "sun" leaves have an extra layer of cells on the upper leaf surface. The light-trapping chloroplasts in sun leaves are arranged vertically along the sides of the cells. This leaf structure allows for efficient use of high light but is very inefficient indoors.
In contrast, plants grown under low light have "shade" leaves designed to trap as much light as possible. They are wider and thinner than sun-grown leaves, and they usually have only one layer of cells on the upper surface. Their chloroplasts are arranged horizontally along the upper cell surface to capture as much light as possible. Mature leaves apparently do not change their size or internal arrangement. The plant can, however, produce shade leaves during a period of acclimation to a low light environment.
Three factors lower the light requirement for a plant moved indoors. First, the plant's growth slows dramatically or even stops. This growth reduction triggers a lesser demand for food. Second, while the existing leaves cannot change their structure, they can increase their chlorophyll content. Third, the new leaves that are produced in the indoor environment will be structured as shade leaves. This has been shown to result in a reduction in the plant's light compensation point.
The light compensation point is defined as the minimum light level at which the amount of food produced by photosynthesis is equal to the amount of food consumed during respiration. Shade leaves have lower light compensation points than sun leaves. Acclimation to low light involves a reduction in the plant's light compensation point either by changes in leaf metabolism so light energy is captured more efficiently in low light or by replacement of inefficient sun leaves with shade leaves tolerant to low light levels.
Artificial light can be used to supplement or replace natural sunlight. Cool-white fluorescent lights used alone or in combination with warm-light fluorescent lights are the most economical and best all-purpose lamps. Typically, a fixture holding two 40-watt tubes is positioned approximately 12 inches above the plants. Most plants need 12 to 16 hours of artificial light per day for good growth. For large specimen plants, use spot or flood lights to maintain good appearance and accent the plant. Lighting design should take into account anticipated use of indoor plants. Indirect and track lighting are very effective design features for this purpose.
Understanding how a plant reacts to temperature stress will increase the interiorscaper's ability to make adjustments to correct problems and improve plant longevity. In addition to problems caused by chilling, heat from registers can dry out media and foliage quickly. A minimum/maximum thermometer will record temperature differences plants may be experiencing in the interior landscape.
Most public buildings are heated and cooled with human comfort in mind rather than the growth requirements of indoor plants. Fortunately, the desirable temperatures for humans fall within the optimum range for most foliage and flowering plants. Daytime temperatures of 70 to 80°F and a nighttime range of 60 to 70°F are satisfactory for most species. Many flowering plants bloom longer at the lower end of these day-night temperature ranges. Variations in temperature ranges should be considered in selecting plants for the interior environment. Temperature ranges for several interior plants are listed in Table 1.
Plants differ in their degree of sensitivity to chilling. Generally, most foliage plants cease to grow at 60°F. Temperatures between 45 and 55° F often result in chilling. Chilling causes changes in cell membrane structure, which, in essence, causes the cells to "leak" their contents. This causes a loss in plant vigor and reduced growth. The damage may not be visible for months after chilling has taken place. Many times a secondary problem such as disease will begin to increase due to the loss of vigor. This secondary problem is then blamed for the damage, and chilling goes undetected.
Chilling damage is very subtle and may be very difficult to detect unless maintenance personnel are looking for it. Symptoms of chilling injury include:
The severity of chilling damage is a result of temperature and length of exposure. For example, exposure to 50°F for 12 hours may cause chilling injury as severe as exposure to 40°F for 2 hours. Chilling injury can result from only a few minutes exposure at freezing temperatures. Plants can get chilled in the truck going to a job site, during transfer from the truck to the indoors, and from exposure to cold winds near doorways. The following conditions can contribute to chilling injury in the interior environment:
Table 1. Light and temperature ranges for selected indoor plants(a)
|LOW LIGHT (25-75 FC)|
|Aglaonema commutatum||Silver Evergreen||Warm|
|Aglaonema commutatum 'Silver King'||Silver King Evergreen||Warm|
|Aglaonema modestum||Chinese Evergreen||Temperate|
|Aspidistra elatior||Cast-Iron Plant||Temperate|
|Aspidistra elatior 'Variegata'||Variegated Cast-Iron Plant||Temperate|
|Chamaedorea elegans||Parlor Palm||Warm|
|Chamaedorea elegans 'Bella'||Neanthe Bella Palm||Warm|
|Epipremnum aureum||Golden Pothos|
|Epipremnum aureum 'Marble Queen'||Marble Queen Pothos|
|Monstera deliciosa||Split-Leaf Philodendron||Warm|
|Sansevieria trifasciata||Snake Plant.||Warm|
|Sansevieria trifasciata 'Laurentii'||Goldband Sansevieria||Warm|
|MEDIUM LIGHT (75-150 FC)|
|Aechmea fasciata||Silver Vase||Warm|
|Aglaonema commutatum 'White Rajah'||White Rajah Aglaonema||Warm|
|Asparagus densiflorus 'Myers'||Plume Asparagus||Temperate|
|Asparagus densiflorus 'Sprengeri'||Sprengeri Asparagus||Temperate|
|Asparagus setaceus||Fern Asparagus||Warm|
|Aucuba japonica 'Variegata'||Gold-Dust Plant||Cool|
|Brassaia arboricola*||Dwarf Schefflera|
|Chamaedorea erumpens*||Bamboo Palm||Warm|
|Chlorophytum comosum 'Variegatum'||Spider Plant||Temperate|
|Cissus rhombifolia||Grape Ivy||Warm|
|Dieffenbachia amoena||Giant Dumbcane||Warm|
|Dieffenbachia amoena 'Exotic'||Exotica Dumbcane||Warm|
|Dieffenbachia maculata||Spotted Dumbcane||Warm|
|Dieffenbachia maculata 'Rudolph Roehrs'||Gold Dieffenbachia.||Warm|
|Dizygotheca elegantissima||False Aralia||Warm|
|Dracaena deremensis 'Warneckii'*||Striped Dracaena||Warm|
|Dracaena fragrans 'Massangeana'*||Corn Plant||Warm|
|Dracaena godseffiana*||Gold-Dust Dracaena||Warm|
|Dracaena marginata*||Red-Margined Dracaena||Warm|
|Dracaena sanderana*||Ribbon Plant||Warm|
|Fatsia japonica||Japanese Fatsia||Cool|
|Ficus benjamina||Weeping Fig||Warm|
|Ficus elastica 'Decora'||India Rubber Plant||Warm|
|Ficus lyrata||Fiddle-Leaf Fig||Warm|
|Ficus retusa||Indian Laurel||Warm|
|Gynura aurantiaca||Velvet Plant||Warm|
|Hedera helix & cvs||English Ivy||Cool|
|Howea forsterana||Kentia Palm||Temperate|
|Maranta leuconeura erythroneura||Red-Veined Prayer Plant||Warm|
|Nephrolepis exaltata 'Bostoniensis'||Boston Fern||Temperate|
|Pandanus veitchii||Variegated Screw Pine||Warm|
|Peperomia caperata*||Emerald-Ripple Peperomia||Warm|
|Peperomia obtusifolia||Oval-Leaf Peperomia.||Warm|
|Peperomia obtusifolia 'Variegata'||Variegated Peperomia||Warm|
|Philodendron bipennifolium*||Fiddle-Leaf Philodendron|
|Philodendron scandens oxycardium*||Heart-Leaf Philodendron||Warm|
|Philodendron selloum||Tree Philodendron||Warm|
|Pilea cadierei||Aluminum Plant||Warm|
|Pilea involucrata||Friendship Plant||Warm|
|Plectranthus australis||Swedish Ivy||Temperate|
|Polyscias balfouriana 'Marginata'||Variegated Balfour Aralia||Warm|
|Saintpaulia spp., hybrids & cvs||African Violet||Warm|
|Spathiphyllum 'Clevelandii'||Cleveland Peace Lily||Warm|
|Spathiphyllum 'Mauna Loa'||Mauna Loa Peace Lily||Warm|
|Syngonium podophyllum 'Trileaf Wonder'*||Trileaf Wonder Nephthytis||Warm|
|Tradescantia fluminensis||Inch Plant||Temperate|
|Zebrina pendula||Wandering Jew||Temperate|
|HIGH LIGHT (150-1000 FC)|
|Aloe barbadensis||Aloe Vera||Warm|
|Alternanthera ficoidea||Joseph's Coat|
|Araucaria heterophylla||Norfolk Island Pine||Temperate|
|Beaucarnea recurvata||Ponytail Palm|
|Cissus antarctica**||Kangaroo Vine||Temperate|
|Crassula argentea||Jade Plant||Temperate|
|Fatshedera lizei**||Botanical Wonder||Temperate|
|Hibiscus rosa-sinensis||Chinese Hibiscus||Warm|
|Hoya carnosa* *||Wax Plant||Temperate|
|Iresine lindenii||Blood Leaf||Temperate|
|Podocarpus gracilior||Weeping Podocarpus||Warm|
|Sedum morganianum||Burro's Tail||Temperate|
(a)Warm ± 62 (night) to 85° F (daytime); Temperate ± 50
(night) to 70° F (daytime);
Cool ±40 (night) to 60° F (daytime).
*May also be conditioned to grow in low light.
**May also be conditioned to grow in medium light.
How the plant is produced greatly influences its long-term survival in the interiorscape. Because approximately 70 percent of the keeping quality of a plant is determined by production practices, plant buyers should develop good working relationships with suppliers and learn about their production practices in order to assure procurement of prime plant material. Price alone should not guide purchase decisions. Ask growers about the light levels used during production, fertilization programs, and pest control practices. Examine plants closely upon arrival—are they free of pests and diseases? The interior environment is tough even on healthy, properly grown plants; poorly handled, low quality material is almost certain to fail.
Most of the plants used in interiorscapes on the east coast are grown in Florida. These plants are often grown in native Florida soil, dug and placed in containers for three to four months, and then sold to interiorscapers. Plants are available in three grades: A, B, and C. Grade "A" is the best, the most expensive, and has the best chance of surviving the interiorscape conditions. Grade "C"plants are often sold from the back end of trucks labeled "Florida Foliage Plants" in mall parking lots. Starting with low-grade plants will lead to more problems than using high-grade plants.
Not only must plants be properly grown, they must be prepared for the change from the production environment to the interior environment.
Large foliage plants are grown in optimum environments outdoors in southern Florida primarily for outdoor landscaping there. Small sizes are grown in greenhouses or set outdoors in desirable growing conditions for the summer. When placed in offices, malls, or hotel lobbies, the plants usually must adjust to lower levels of light, relative humidity, and nutrients, longer intervals between irrigations, and drier growing medium. Long-term survival in the interior environment depends on the plant's condition and its tolerance for interior conditions. Tolerance can be improved by gradually acclimating the plant to the new environment.
Acclimation depends on adequate light to support the growth processes while the plants adjust to lower light environments. The minimum time required for acclimation varies by plant species but the recommended light levels for most plants are 12 hours of 2000 foot-candles. During the acclimation period plants should also be leached thoroughly to reduce the salt and nutrient levels in the growth medium. Watering should be gradually reduced to one or two times per week, and fertilizer should be withheld. Acclimated plants have a more extensive root system (a smaller shoot to root ratio), and resist drying damage to the foliage.
The need for acclimation is greatest when plants have been grown in high light conditions. Large specimen trees, for example, require full light during production to generate adequate stem caliper and strength, and they require acclimation before going into an interior setting. In addition to preparing plants for the interior, acclimatization causes a more desirable, darker green color in palms and Brassaia spp.
Not all foliage plants need acclimation. Transition to the interior environment without acclimation is most successful if the plants have been produced in shade or when interior light levels are high with skylights, glass walls, or actual greenhouse-like architecture.
In general, acclimation is needed:
Once plants have been properly placed in the interiorscape, their appearance needs to be sustained through proper maintenance and care. Usually, this is limited to watering, fertilizing, cleaning, and pruning.
Watering indoor plants is a widely misunderstood practice. Water content in the container and plant-water needs are difficult to measure accurately. As a result, improper watering is the underlying cause of many plant problems. There are several basic points to consider when deciding when to water:
In a routine maintenance program, most plant installations will be watered once every 7 to l0 days. Generally, when the top half-inch of the soil in containers up to 8 to 10 inches in diameter feels dry, the plant probably needs watering. The plants on one job site might be from five different growers and in five different media, therefore, some plants will be underwatered and some will be overwatered. Overwatering actually excludes oxygen from the root zone. This prevents active water uptake and effectively shuts down the supply of water to the leaves, resulting in the same symptoms as underwatering. Such symptoms include: wilting, loss of older leaves, brown foliage tips or margins, small new leaves, and lack of new growth.
Correct watering practices can reduce many cultural problems of indoor plants; conversely, poor watering practices may aggravate plant problems.
To minimize water-related problems:
Check with your local county extension office if a high water-salt level is suspected. A water analysis can be requested from a qualified laboratory.
Fertilization is necessary for growth and maintenance of plants. A plant's need for fertilizer depends on its growth rate, the amount of leaching that occurs during watering, soil volume, and other factors. Fertilizer levels that were ideal during production can severely damage plants in interiorscapes. Soluble salts in the media can cause root burn when too much fertilizer is applied, when the medium dries out, and when water quality is poor.
Generally, when a plant leaves the production area there will be no further net increase in root-ball size. Any condition or practice that reduces root numbers will stress the plant and reduce plant longevity. Stress may be caused by high soluble salts, overwatering, underwatering, or poor water quality. At best, the rate of root replacement indoors will be very slow.
"Nutrient acclimation" of growing media is crucial for best plant performance in the interior environment. Media must be leached and the plant acclimated to reduced nutrient and salt levels before the plant is installed indoors.
One of the most devastating problems facing an interiorscaper is "Tiny Feet." Foliage plants react very strongly to high levels of fertilizer in production. They produce very large tops, but do not develop a similar root mass. This results in "Tiny Feet". While in production under high humidity, the plants look fine and finish sooner than plants grown under lower fertility. However, when moved indoors under low humidity, the demand for water by the leaves will be greater than the roots can supply, so the plant becomes water stressed. The plant begins to drop leaves, turn yellow, and may eventually die. Nothing can be done to correct this problem. It is prevented by purchasing plants from growers who use proper fertility in production.
Nutrient monitoring is very important in maintaining the interiorscape. It is highly recommended that growth media be tested by the North Carolina Department of Agriculture Soil Testing Service prior to planting. Test results will indicate whether adjustments should be made to the medium to reach optimum nutrient levels. Once optimum nutrient levels are established, they can be maintained by carefully planned fertilization practices. For a small fee, NCDA also does tissue analysis.
Generally, interior plantings should be fertilized a maximum of four times per year. As a rule, applications should be more frequent during the spring and summer when sunlight intensity increases and days are longer. During the short days of winter, many indoor plants that receive little or no artificial light enter a resting stage. If plants go into a winter rest period, it's best to give them little, if any, fertilizer. Plants that have just been transplanted or repotted will obtain sufficient nutrients from the fresh potting soil for at least 4 to 8 weeks. They do not require supplemental fertilizer during this time.
Triple superphosphate is a common source of phosphorus for container soils. It should not be routinely used for foliage plants because it also contains toxic fluoride ions. Thus to avoid fluoride and salt residues, a balanced fertilizer should be composed of salt combinations such as KNO3 and (NH4)2HPO4 or (NH4)3 PO4.
Slow release fertilizers such as dry, garden formulations provide nutrients over several months. Formulations that contain nitrogen only in the ammonium form are not used because toxic levels of ammonium commonly develop. The "membrane types" of slow release fertilizers are expensive per unit nutrient applied, but are less labor intensive because they are applied less frequently.
As the medium dries out, the soluble salt concentration goes up. If the plants are allowed to dry out, high salts may damage roots. Groundwater with relatively high concentrations of salts may also be a source of damage to salt-sensitive plants.
Plant cleaning includes dust and water-spot removal, leaf shining, and removal of senescent leaves. The leaves of indoor plants can become coated with a heavy layer of dust in a surprisingly short time. This dust and grime interferes with normal leaf functions and makes the plant less attractive. Accumulated dust will shade the leaves and may so drastically reduce light that the plant will eventually die. Dust with a soft brush or cloth moistened with warm water to clean both upper and lower leaf surfaces at least every two or three months.
Cleaning frequency and method depends, in part, on leaf characteristics. For example, hairy leaves (such as on Velvet Plant) will collect dust and require occasional brushing. Shiny, waxy leaves (as in Peperomia) readily show dust and must be wiped periodically with a damp cloth. If the upper side of the leaf is concave or has an uneven rippled surface, it will collect dust that should be removed with a gentle mist spraying or brushing. Finally, if the plant leaves grow more horizontally than at an angle, they will collect dust more easily.
Dust can be a tremendous maintenance problem in large-scale plantings. Ease of maintenance should be a consideration in selecting plants for a particular location. More dust is likely to accumulate where the ventilation system is open than in air-conditioned locations where it is closed. Accessibility of installed plants for cleaning is a further consideration. If plants are not easily accessible, only the most dust-resistant ones should be chosen. Dusting will not present as much of a problem in homes, but in commercial installations, accessibility of plants and the availability of maintenance staff are additional considerations. In some instances, large plant material is best cleaned by washing off the foliage.
Several leaf-cleaning compounds have been tested on Philodendron scandens subsp. oxycardium. All products seem adequate. However, reductions of plant growth probably are caused both by the product as well as the degree of leaf abrasion during application.
Plants that are small enough to move into the shower or outdoors for a mild soapy wash and rinse in warm weather will be more attractive and less prone to insect problems. Plant leaf-shine materials should be avoided. They attract dust and can slow plant growth.
Interior plants often grow at a slow rate, but to the extent that they increase in size, they will require maintenance. Plants with mechanical damage or those under environmental stress will also require maintenance. Pinching, disbranching, and shaping-from removing a shoot tip to encourage branching to removing an entire section of the plant to maintain its intended design size-may be necessary occasionally. Another reason for pruning may be the removal of insect pests such as scales that may accumulate on specific branches.
If light comes from one direction, plants should be turned regularly if possible to expose all sides to light. This encourages a more uniform shape. Remove yellow or discolored foliage as it develops. Dried brown leaf tips and margins may be trimmed back to green tissue with scissors. Follow the shape of the leaf when making these cuts to maintain the natural appearance.
This material was adapted from the following resources:
Bailey, Douglas. 1994. Indoor plant selection and care. North Carolina Cooperative Extension Service. Horticulture Information Leaflet 554.
Bailey, Douglas. 1983. Selection and care of foliage plants. Proceeding of the North Carolina Interior Plantscape Symposium.
Fonteno, William. 1993. Stress Physiology: What is your plant telling you? Proceedings of the North Carolina Interior Plantscape Symposium.
Thanks to Dr. Alice Russell, Extension Specialist, Consumer Horticulture for reviewing this chapter.