Indoor Plants - Cleaning, Fertilizing, Containers & Light Requirements

Prepared by Debbie Shaughnessy, HGIC Horticulture Specialist, and Al Pertuit, Extension Floriculture Specialist, Clemson University. (New 09/99.)

HGIC 1450

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Indoor plants are widely used in homes and commercial buildings such as offices, restaurants and shopping malls. They help us stay in touch with nature and, in a sense, "bring the outside indoors."

Cleaning

Indoor plants may collect dust or greasy films that dull their appearance, making them less attractive. Clean leaves are favorable to healthy growth. Also, cleaning helps control insects and enhances the plants' attractive-ness. Products that clean and shine leaves are generally not recommended because the waxy coating residue may interfere with air exchange. Never use these products on plants that have hairy leaves, such as African violets.

The best way to clean leaves that are not hairy is to dampen a soft cloth with water and wipe the lower and upper surfaces of each leaf. An alternative is to place the entire plant outdoors or in the shower to rinse it off. Plants with hairy leaves should not be dusted with a wet cloth but with a soft cosmetic brush. A pressure sprayer may be employed.

Fertilizing

All plants require certain essential elements for proper growth. Indoor plants, in low light conditions of the interior environment, have reduced fertilizer requirements.

Observation will guide you in determining a plant's fertilizer needs. As a rule, applications should be more frequent when the plants are in their growth stage(s). This is usually in the spring and summer when sunlight intensities increase and the days are warmer and 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, do not give them fertilizer.

Frequency of fertilizer application varies somewhat with the vigor of growth and age of each plant. Rapid, new growth is often undesirable, as plants may outgrow their locations. As a rule, fertilizer applications should be more frequent when the plants are growing. Fertilize at the recommended label rate every two or three months, or dilute the fertilizer to about one-tenth the recommended rate and use this solution at every watering during the growing season. An alternative to these methods is to fertilize every seventh watering.

A complete fertilizer (one that contains nitrogen, phosphorous and potassium) is an excellent choice for indoor gardens. Choose a balanced fertilizer for foliage plants, such as 20-20-20, and one that is higher in phosphorous for flowering plants, such as 15-30-15. These numbers represent the percents by weight of nitrogen, phosphorus and potassium in the fertilizer.

Fertilizers are available for indoor plants in liquid form, water-soluble granules and slow-release forms (granules, stick or tablets). Water-soluble fertilizers are often preferred because dilute solutions reduce the potential for fertilizer burn.

Soils that have a white film on the surface or pots with a white crust on the rim or drainage hole may indicate that the plant is being overfertilized and/or possibly overwatered. Salt buildup in the soil can lead to root damage, causing symptoms such as reduced growth, brown leaf tips, dropping of lower leaves and wilting of the plant.

The most effective way to prevent soluble salt injury is to prevent the salts from building up. Water correctly by watering the soil thoroughly and allowing the excess to flow out of the drain holes into a tray which is emptied.

Indoor Containers

Many types of containers can be used for growing plants. Most pots with bottom drainage holes are made of plastic, ceramic or clay, whereas decorative containers without drainage holes may be made of clay, ceramic, plastic, wood, copper, brass and various other materials.

It is important to choose the correct size container for the plant. Containers too small or too large present an unbalanced appearance. An appropriate container should provide room for soil and roots, allow sufficient headroom for proper watering, and be attractive without competing with the plant.

Two methods for potting indoor plants are: (1) planting directly in the container and (2) placing a potted plant in another, more decorative container ("double-potting"). When plants are potted directly in the container, the container should have a drainage hole and a tray to catch the excess water. If the pot does not have a drainage hole, place a layer of coarse gravel in the bottom to allow a space for excess water (it is important not to saturate soil in such containers). The "double-potting" technique can be used with decorative containers with or without drainage holes. The smaller, interior pot should have a drainage hole. If the decorative pot does not have a drainage hole, place a layer of gravel in this pot, and place the potted plant on the gravel layer. No gravel layer is necessary if the decorative pot has a drainage hole. Be sure to place a tray beneath the pot to catch the excess water. Never place pots directly in contact with the carpet, floor or furniture as moisture can damage its surroundings.

Clay pots are porous and allow air movement through the sides of the pot. This allows the soil to dry and oxygen to reach the roots. Nonporous containers prevent water from evaporating through the sides, thus, plants require less frequent watering than those in clay pots.

Light Requirements

The environment in our homes dictates which plants will grow vigorously and which will suffer. The most important environmental factor in growing plants indoors is adequate light.

Light provides the energy source needed for plants to manufacture food. The amount of light is commonly measured in foot-candles (ft-c). The interior of a well-lighted home is often less than 100 ft-c, while outdoor light intensity on a clear sunny day may exceed 10,000 ft-c. Plants differ greatly in their light intensity requirements (see table). Indoor plants are often classified by the amount of light necessary for growth:

  • Low (minimum 100 ft-c, 75 to 200 preferred for good growth)
  • Medium (minimum 100 to 150 ft-c, 200 to 500 preferred)
  • High (minimum 150 to 1000 ft-c, 500 to 1000 preferred)
  • Very high (minimum 1000 ft-c, 1000+ preferred)

About 100 ft-c for 12 hours per day are necessary simply to maintain plant quality for one year, and at least 200 ft-c for 12 hours per day are necessary for foliage plants to manifest any benefit from fertilization.

With the exception of homes with a sunroom or greenhouse, few homes have areas with sufficient light levels to grow plants that require very high light (hibiscus, wax begonia, geranium). High light plants (weeping fig, English ivy, schefflera) can usually be grown well near windows or glass doors with western or southern exposures. Medium light plants (African violet, Boston fern, dumb cane) do well if placed within several feet of these light sources or in eastern exposures. Low light plants (peace lily, heart-leaf philodendron, cast-iron plant) can be placed several feet away from eastern exposures or in northern exposures. The amount of light at any given location will vary according to time of year (angle of the sun, day length), outdoor tree shading, window curtains and wall color (light reflection), as well as the location itself. Inexpensive light meters are available.

Artificial lighting is widely used to supplement or replace natural light. Many indoor plants grow well under artificial light provided by fluorescent lamps or special incandescent lights. A large variety of fluorescent lamps are available. Generally, ordinary incandescent lamps are not recommended for plants, as plants placed under them tend to stretch or become "leggy." It is possible to make up for lack of sufficient light by increasing the time or duration that the plant is exposed to light. Sixteen hours of light and eight hours of darkness are satisfactory for most plants. Use an electric timer to ensure the correct cycle each day.

While lack of sufficient light results in poor plant growth, too much light can also be harmful. Shade plants cannot tolerate excessively high light levels. When a plant receives too much direct light the leaves bleach or scald, sometimes dying. This often happens after moving a plant outdoors in direct light. Any changes in light intensity should be gradual.

Light Requirements in Footcandles (ft-c)
for Some Common Indoor Plants Low Light (100 ft-c)
Botanical Name Common Name
Aglaonema commutatum Silver Evergreen
Aglaonema commutatum cv. Silver King Silver King Evergreen
Aglaonema modestum Chinese Evergreen
Aspidistra elatior Cast-iron Plant
Aspidistra elatior cv. Variegata Variegated Cast-iron Plant
Chamaedorea elegans Parlor Palm
Epipremnum aureum Golden Pothos
Epipremnum aureum cv. Marble Queen Marble Queen Pothos
Monstera deliciosa Split-leaf Philodendron
Sansevieria trifasciata Snake Plant
Sansevieria trifasciata cv. Laurentii Goldband Sansevieria
 
Light Requirements in Footcandles (ft-c)
for Some Common Indoor Plants - Medium Light (100 to 150 ft-c)
Botanical Name Common Name
*May also be conditioned to grow in low light.
Aechmea fasciata Silver Vase
Asparagus densiflorus cv. Myers Plume Asparagus
Asparagus densiflorus cv. Sprengeri Sprengeri Asparagus
Asparagus setaceus Fern Asparagus
Aucuba japonica cv. Variegata Gold-dust Plant
Brassaia actinophylla* Schefflera
Brassaia arboricola* Dwarf Schefflera
Caryota mitis Fishtail Palm
Chamaedorea erumpens* Bamboo Plant
Chlorophytum comosum cv. Variegatum Spider Plant
Cissus rhombifolia Grape Ivy
Dieffenbachia amoena Giant Dumbcane
Dieffenbachia maculata Spotted Dumbcane
Dizygotheca elegantissima False Aralia
Dracaena deremensis cv. Warneckii* Striped Dracaena
Dracaena fragrans cv. Massangeana* Corn Plant/td>
Dracaena godseffiana* Gold-dust Dracaena
Dracaena marginata* Red-margined Dracaena
Dracaena sanderana* Ribbon Plant
Fatsia japonica Japanese Fatsia
Ficus benjamina Weeping Fig
Ficus elastica cv. Decora India Rubber Plant
Ficus lyrata Fiddle-leaf Fig
Ficus retusa Indian Laurel
Gynura aurantiaca Velvet Plant
Hedera helix and cultivars English Ivy
Howea forsterana Kentia Palm
Maranta leuconeura cv. Erythroneura Red-veined Prayer Plant
Nephrolepsis exatata cv. Bostoniensis Boston Fern
Peperomia caperata* Emerald Ripple Peperomia
Peperomia obtusifolia Oval-leaf Peperomia
Philodendron bipennifolium* Fiddle-leaf Philodendron
Philodendron scandens subsp. oxycardium* Heart-leaf Philodendron
Philodendron selloum Tree Philodendron
Pilea cadierei Aluminum Plant
Pilea involucrata Friendship Plant
Plectranthus australis Swedish Ivy
Polyscias balfouriana cv. Marginata Variegated Balfour Aralia
Saintpaulia species, hybrids and cultivars African Violet
Spathiphyllum cv. Clevelandi Cleveland Peace Lily
Spathiphyllum cv. Mauna Loa Mauna Loa Peace Lily
Syngonium podophyllum cv. Trileaf Wonder* Trileaf Wonder Nephthytis
Tradescantia fluminensis Inch Plant
Zebrina pendula Wandering Jew
 
Light Requirements in Footcandles (ft-c)
for Some Common Indoor Plants -  High Light (150 to 1000 ft-c)
Botanical Name Common Name
**May also be conditioned to grow in medium light.
Aloe barbadensis Aloe Vera
Alternanthera ficoidea Joseph's Coat
Aphelandra squarrosa Zebra Plant
Araucaria heterophylla Norfolk Island Pine
Beaucarnea recurvata Ponytail Palm
Cissus antarctica** Kangaroo Vine
Citrofortunella mitis Calamondin Orange
Coffea arabica Coffee
Coleus blumei Coleus
Cordyline terminalis Ti Plant
Crassula argentea Jade Plant
x Fatshedera lizei** Botanical Wonder
Hibiscus rosa-sinensis Chinese Hibiscus
Hoya carnosa** Wax Plant
Iresine lindenii Blood Leaf
Podocarpus gracilior Weeping Pododarpus
Polyscias fruticosa Ming Aralia
Rhoeo spathacea Moses-in-the-Cradle
Schlumbergera cv. Bridgesii Christmas Cactus
Sedum morganianum Burro's Tail

Excerpted from the South Carolina Master Gardener Training Manual, EC 678.

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