Encyclopedia
A
houseplant is usually a tropical or semi-tropical
plant that is grown indoors in places such as
residences and
offices. Houseplants are commonly grown for decorative purposes and health reasons such as indoor air purification.
Caring for a houseplant
Major factors that should be considered when caring for houseplants are moisture, light,
soil mixture, temperature, humidity,
fertilizers, potting, and pest control. The following includes some general guidelines for houseplant care. For specific houseplant needs, the tags that sometimes come with plants are notoriously unhelpful and generic. Find care instructions for the species in a book or online.
Moisture
Both under-watering and over-watering can be detrimental to a houseplant. The best way to determine whether a plant needs water is to check the soil moisture. To do this, use your finger, as moisture meters are notoriously inaccurate. Potted plants must be allowed to reach an appropriate level of dryness in between waterings, and what that is varies greatly depending on the type of plant. Proper soil moisture can range from still slightly moist on the soil surface to very dry to nearly the bottom of the pot. Watering a plant by the calendar is not recommended. If a plant does need to be watered, pour water slowly over the surface of the soil until it begins to drain out the bottom of the pot, ensuring complete saturation. However, sometimes the soil separates from the sides of the pot, allowing the water to flow down the sides of the rootball and out the bottom too quickly to be absorbed and retained by the soil and roots. If this is the case, it may be necessary to set the plant in a shallow dish of water long enough for it to soak up enough water to moisten the rootball to its center. Repotting should eliminate this problem.
Light
Through the process of
photosynthesis, plants convert the energy in sunlight to chemical energy, which fuels plant growth. The two important factors for providing light to a house plant are
intensity and
duration.
Different plants require different light intensities. Intensity of light is difficult to measure without a light meter. It is usually measured in units of lux. 100 lux or less is usually considered "low intensity" or "indirect" lighting. A bright office has about 400 lux of illumination. 1,000 lux or more is usually considered "high intensity" lighting. Direct outdoor sunlight is in the range 32,000-100,000 lux.
The duration of light exposure is as important as the intensity. Quality exposure of 8 to 16 hours is ideal for most plants.
Windows are the most common sources of light for houseplants. In the Northern Hemisphere, south-facing windows have the most sun exposure, while western, eastern, and north-facing windows have progressively less exposure. Natural sunlight through windows is affected by seasonal changes, cloud cover, and window treatments.
Artificial light sources can provide an alternative or supplement to window lighting. Fluorescent lighting provides excellent light quality whereas standard incandescent bulbs do little to promote plant growth. "Cool", or "blue", fluorescent lights provide the light needed for green foliage plants, while "warm", or "red", fluorescent lights provide the light needed for blooming flowers. Fluorescent bulbs that fit into standard screw-in light sockets are readily available.
Soil
Houseplants are generally grown in specialized soils called
potting compost or
potting soil, not in local natural
soil. A good potting compost mixture includes soil conditioners to provide the plant with nutrients, support, adequate drainage, and proper aeration. Most potting composts contain a combination of
peat and
vermiculite or
perlite. Concern over
environmental damage to
peat bogs, however, is leading to the replacement of peat by
coir , which is a sustainable resource. A nutrient rich compost can usually be bought wherever potted plants are sold.
If local natural soil is to be used, it should first be heat sterilized by placing the soil in an oven at 90°
C for at least 30 minutes. This will ensure that the soil does not contain any harmful bacteria. Most locals soils, especially those with a high proportion of clay, do not drain well enough to be a suitable growing medium for houseplants. Coir or peat is used to increase aeration and make heavy soils more absorbent. Vermiculite and perlite aid in drainage in a soil mixture. Perlite is recommended over vermiculite because it does not break down as easily. A coarse grade
sand or grit can be used as a substitute for a drainage mechanism if needed. These three ingredients can be mixed in varying ratios to create different potting soil types. For a plant that requires fast drainage, such as a
cactus, use plenty of coarse sand, grit or perlite. For a plant that requires plenty of moisture, use more coir. A good all purpose soil mixture is 2 parts coir and 1 part perlite or vermiculite. A so-called "heavy soil mix" will contain sterilised soil, milled
sphagnum moss or coir, and perlite in equal proportions. It is also possible to make a soil mixture that actually contains no soil by mixing equal parts peat moss and perlite . The soiless mixture will retain more moisture.
Temperature
Most houseplants are tropical species selected for their adaptation to growth in a climate which ranges from 15°C to 25°C, similar to the temperature in most homes. Temperature control for other plants with differing requirements needs attantion to heating and/or cooling.
Humidity
Humidity is slightly more difficult to control than temperature, but is less important. The more commonly used houseplants have established that they can survive in low humidity environments as long as their roots are kept properly irrigated. Most plants thrive in 80% relative humidity while most homes are usually kept around 20% to 60% relative humidity. Besides buying a humidifier, there are a few things that can be done to increase humidity around houseplants. One of the most popular methods used to raise the ambient humidity around a houseplant is to use a pebble tray which is made by filling the drainage pot used by the plant with small pebbles, rocks, polished glass or similar material. The tray is then filled with water and over time the water will evaporate and increase the humidity around the plant. Other methods of raising humidity include grouping plants closely together and not placing plants in drafty areas. Misting plants does little to raise the humidity of plants.
Fertilizers
In a potted environment, soil nutrients can eventually get depleted. Adding fertilizer can artificially provide these nutrients. However, adding unneeded fertilizer can be harmful to the plant. Because of this, careful consideration must be taken before fertilizing. If a plant has been in the same potting mix for a year or more and is growing vigorously, the it may be a candidate for nutrient replacement done by using a complete fertilizer at half the recommended label dilution rate.
Fertilizers are usually marked with a number such as 20-20-20. These numbers indicate the percentages of
nitrogen,
phosphorus, and
potassium, elements that are needed for plant growth. A 3-1-2 ratio of these elements is usually good for green foliage plants, while a 1-2-1 ratio is usually better for flowering plants. A complete fertilizer will also include the minor and trace elements, such as calcium, magnesium and iron.
While variation may occur between brands, a general rule is to mix 1 tablespoon to every gallon of water. In all cases, it is better to under-fertilize than over-fertilize. The diluted mixture is then used to water the plants. The growth of the plants should be monitored to determine if the fertilizer is helping or harming, and how often it should be used. Schedules can range from every other week to every three months.
Pot types and sizes
Proper pot size is an important factor to consider. A pot that is too large will cause root disease because of the excess moisture retained in the soil, while a pot that is too small will restrict a plant's growth. Generally, a plant can stay in the same pot for two or so years. Pots come in a variety of types as well, but usually can be broken down into two groups: porous and non-porous. Porous pots are usually clay and are highly recommended because they provide better aeration as air passes laterally through the sides of the pot. Non-porous pots such as glazed or plastic pots tend to hold moisture longer and restrict airflow. Another needed feature is drainage holes. Usually pots come with holes in the bottom to allow excess water to flow out of the soil which helps to prevent root rot. If a pot does not have drainage holes, it is best to double pot that plant so the inner pot can be lifted out and the excess water accumulated in the bottom of the outer pot can be removed. Wash old pots thoroughly in a dishwasher or by hand to kill any bacteria that may remain.
List of common houseplants
Tropical houseplants
Others
See also
References
- , HGIC 1456, Clemson University Cooperative Extension Service
- , National Sustainable Agriculture Information Service
