HO-103 Indoor Plants

University of KentuckyCollege of Agriculture,Food and EnvironmentHO-103Cooperative Extension ServiceIndoor PlantsKentucky Master Gardener Manual Chapter 14By George Pinyuh, extension agent emeritus, King and Pierce counties; E. Blair Adams, extension horticulturist (deceased); Arthur L.Antonelli, extension entomologist; and S.J. Collman, extension agent emeritus; all of Washington State University. Adapted for use inKentucky by Sharon Bale, extension horticulture specialist.In this chapter:Management.191Potting and Repotting.194Houseplant Problems.198Cultivating plants inside the home is both a popular hobbyand an interior decorating technique. More than 75 percentof all American families use living plants as part of theirhome decor or cultural expression.To keep plants healthy and attractive, you must control a number of environmental factors such as light, temperature, humidity,water, and plant nutrients. The right combination results in healthyplants. Too much or too little of any factor results in poor planthealth or death.A houseplant is simply an outdoor plant that is grown indoors.Not all plants are suitable for indoor culture. Some require environmental conditions that are impossible to duplicate indoors. Othersadapt to indoor culture if their minimum growth requirementsare provided. The key to successful indoor plant culture is to selectplants that are adaptable to the conditions in your home.The normal home provides a number of different environments. Light varies from sunny windows to dim corners. Plants inliving areas receive long hours of light (either natural or artificial)year-round, but those in bedrooms normally receive only minimalsupplemental light. Humidity usually is much higher in kitchensand bathrooms than in living rooms. Temperatures vary widely. Theoverall climate may range from humid subtropical to arid desert invarious locations.ManagementThe environmental factors of light, temperature, and humidityare to a large extent determined by how you manage your homeenvironment for family comfort. Other environmental factors, suchas water and nutrient availability, can be managed solely for yourplants’ sake. By selecting the best site for each plant and managingthe supply of water and nutrients, it is possible to grow most common houseplants in any home.Each plant has its own set of desired environmental conditions.There are many sources of information for specific cultural requirements. Check with the store that supplied the plant or with localcounty extension agents. Houseplant books (there are hundreds,many available at libraries), and garden encyclopedias (also available at libraries) are also a source of information.Cooperative Extension Service Agriculture and Natural Resources Family and Consumer Sciences 4-H Youth Development Community and Economic Development

192 Indoor PlantsChapter 14LightPerhaps the major environmental factorlimiting plant growth indoors is lack of adequate light. As natural light enters homes, itdecreases very quickly. For example, a plant1 foot away from a window may receive100 foot-candles of light. If it is moved 2feet away from the window, it will receiveonly 25 foot-candles of light. At 3 feet itreceives only 11 foot-candles, and very few,if any, houseplants do well at such low lightintensities.The most expedient method of adjustinglight intensity is to move the plant closerto or farther from a light source such as awindow. Unfortunately, this may place theplant in an inconvenient spot.In general, a plant needs an environment as similar as possible to that in whichit grows naturally. Understory plants (thosethat live on the forest floor) can grow in diffuse light. Plants from deserts or other openenvironments require strong light. Tropicaland subtropical species generally do bestin humid conditions, and desert speciesrequire arid conditions. Cool-climate species prefer cool nights and warm days, whiletropical species prefer warm temperaturesat all times. Learn about the specific plantsyou are growing (or plan to acquire) andplace them in a location that provides thebest combination of environmental factorsfor their needs.Cultivating houseplants is enjoyable andrewarding. The basic culture is not difficult,and most plants require only a few minutesof attention each week once their basicenvironmental requirements are satisfied.They do, however, require this minimal careon a regular basis. Plants are living thingsand must be managed so that their life-support systems function properly at all times.The following sections discuss severalimportant aspects of plant care.To increase light intensity you can: Moving the plant to a lighter room(southern versus northern exposure) Placing the plant near an electric light Providing separate artificial light for theplant Providing reflected light with a lightcolored wall or mirror Keeping leaves free of dust and grimeTo reduce light intensity you can: Place a lace curtain between the plantand window Use venetian blinds to intercept anddivert direct sunlight Reduce reflected light with a darkbackdrop Shade the plant with another plant Move the plant back from a strong lightsource (for example, a south-facingwindow)TemperatureHome temperatures are adjusted for thecomfort of people, but temperatures varyconsiderably in most homes. Bedroomsusually are cooler than bathrooms or livingareas. Southern-exposure rooms usuallyare warmer during the day than northernexposure rooms. Fortunately, most plantstolerate a fairly broad range of temperaturesand thrive at normal home temperatures ifother environmental factors are satisfactory.

Indoor Plants 193Chapter 14HumidityMany plants require a more humidclimate than the average home. Ferns, ivies,and other humid-climate plants may growbest in bathrooms or kitchens, where theair usually is more humid. You can increaserelative humidity around a plant by placing its pot on a shallow tray of moist gravel(Figure 1a). The gravel will evaporate waterinto the air around the plants.Damp sphagnum moss packed betweenpots in planters also evaporates water intothe air (Figure 1b). Moss has the addedadvantage of acting like a wick to draw upand dispose of excess water in the bottom ofthe planter box.Figure 1. Two ways toincrease humidity arounda plant: (a) A layer ofmoist gravel or pebblesin a tray beneath the potand (b) a pot inside alarge planter filled withmoistened sphagnumpeat moss.a) Gravelb) Sphagnum mossGrouping plants together in the sameroom raises the relative humidity for all.Plants transpire (emit moisture) water continuously. The more plants you grow, themore water they transpire into the air.A humidifier is another way to raisehumidity. The higher relative humidity thatplants prefer also is healthier for people.Misting plants does not significantlyincrease humidity. It may, however, helpkeep leaves clean, which also is desirable.WaterWatering is the most important (andmost often abused) cultural practice. Plantsmust have a continuous and adequate supply of water, but they can absorb water fromthe soil only under certain conditions.First, there must be available water inthe soil. Soil particles hold some watertoo firmly for plants to take up. The wateravailable to plants is water in excess of thatrequired to satisfy the soil itself. The quantity and type of soil mix will determine howmuch water the pot retains for plant use.Second, some air must be in the soil forplant roots to function and absorb water.Therefore, the soil must not contain somuch water that no room is left for air. Agood potting soil will not hold too muchwater if a hole in the bottom of the container allows excess water to drain away.The difference between these twoextremes (no available water versus saturated soil) is called the available water supply. Proper water management avoids bothextremes and maintains a supply of available water at all times.The following guidelines may help youestablish a satisfactory watering schedule: Use a well-prepared potting soil to assuregood water-retention capacity as well asspace for air. Make sure containers have at least onedrainage hole so excess water can drainaway. When watering, apply enough water torun out the drainage hole. This usuallyassures that you have replenished theavailable water supply and also reducessalt buildup. Do not let pots sit in excess water. Pourit away or raise pots so they always areabove the level of drained-out water inthe saucer. Do not water on a time schedule. Allowthe soil to become dry on the surfacebefore you water again. This methodmaintains a good balance of air andwater in the soil. If some plants require frequent watering,move them into slightly larger pots (withgreater water-holding capacity). Some plants, such as desert cacti andsucculents, should be watered only alittle, if at all, during the short days ofwinter. With the exception of seedlingsand very young plants, these plants needno water from about mid-November tomid-March. Most cacti and many succulents are best kept bone-dry and quitecool during the winter.

194 Indoor PlantsChapter 14 Highly organic soils are difficult to rewetonce they dry out. They also tend toshrink away from container sides. Thiscan allow water to run between the soiland the inside of the pot without evermoistening the soil. If this happens, submerge the entire pot in water until themedium is fully moistened. Flush soluble salts from pots on a regularbasis, about every six months. Waterthree times at 30-minute intervals towash salts out the drainage hole.Keep these additional factors in mindwhen watering: Chlorine in tap water will not harmplants. Fluoride in tap water can damage sensitive plants. (See Table 1.) Room-temperature water is best. Plantssuch as African violets and their relativesmay require even warmer water.NutrientsPlants growing in containers have alimited volume of soil from which to extractmineral nutrients (fertilizer). The supply ofnutrients rapidly becomes exhausted whenthe plant is actively growing. Replenishnutrients regularly. The easiest way is towater them in with a solution of solublefertilizer.Many soluble fertilizers are available ingarden stores. Since they vary in strength(percent of fertilizer nutrients), dilute ordissolve them in your watering can according to the label directions. Mix only enoughsolution to water your plants once eachtime you fertilize.During the long days of the year (Easterto Thanksgiving), when plants are activelygrowing, fertilize about every otherweek. During the short days of the year(Thanksgiving to Easter), fertilize only every4 to 6 weeks. If plants are totally dormant,do not fertilize until new growth starts.Here are some fertilizing hints: Slow or time-release fertilizers are a goodway to fertilize houseplants. Follow labeldirections. Plants grow best with small amounts ofnutrients constantly available. Do not apply fertilizers to dry soil. Do not overfertilize. More is not better.Plants can die from too much fertilizer.It’s better to underdo than overdo. Both organic and synthetic fertilizers areacceptable sources of plant nutrients.Potting and RepottingCultivating plants in containers requiresoccasional replanting from one containerto another. Small, rapidly growing plantsmay require repotting into larger containersevery three to four months. You can repotmature houseplants on an annual basis orallow them to remain in containers untilthey have outgrown them or become potbound (Figure 2). If a plant is not doing well,and no obvious reason can be found, it maybenefit from repotting.Handle plants carefully when pottingor repotting to avoid injury and to provideoptimum growth in the new container.When transplanting, consider such factorsas size and condition of the plant, size andtype of container, type and amount of soilmixture, and prevention of damage to theplant.Figure 2. If roots are growing out of the drainage hole,it’s time to repot.