This chapter is designed to familiarize you with the basic aspects of indoor plant care rather than attempting to acquaint you with specific cultural requirements of the more than 250 common plants available for indoor growth. Indoor plant gardeners need to carefully select plants that can best withstand the conditions of a specific indoor location, as home and office locations are often challenging environments for plants to thrive.

Purchasing an Indoor Plant

When purchasing a plant, consider the environmental conditions of where it will live, such as light, temperature, humidity, and ventilation. Select plants that are sturdy, clean, well-potted, and shapely. Plants which have new flower and leaf buds along with young growth are usually of superior quality.

Choose plants with healthy foliage. Check the undersides of the foliage and the axils of leaves for signs of insects or disease.

Avoid plants which have yellow or chlorotic leaves, brown leaf margins, wilted foliage, spots or blotches, or spindly growth. In addition, avoid those with torn leaves and those which have been treated with “leaf shines,” which add an unnatural polish to the leaves.

Remember that it is easier to purchase a plant which requires the same environmental conditions your residence has than to alter the environment of your home to suit the plants.

Transporting House Plants

When transporting plants, remember that heat or cold weather can cause damage to the plants. In the summer, avoid leaving the vehicle shut because temperatures will rise and destroy the plant in a short period of time. The plant can be burned by the sun shining on it even though the air conditioner is on and it’s comfortable in the vehicle. Shade the plant from direct sun while it is in the vehicle.

Transporting a tropical indoor plant in very low temperatures can kill or severely damage plants. During the winter, you may need to wrap plants with newspaper or paper bags, place in the front of the vehicle, and turn on the heater. In most vehicles, the trunk or covered truck bed is too cold to carry plants safely during winter.

On an extended trip, make special arrangements so that plants will not be frozen or damaged by cold weather. Many foliage plants will be damaged considerably if the temperature drops below 50ºF, so maintain as warm a temperature as possible around these plants when transporting them from one location to another. Never allow wind to blow across them from open car windows.

Acclimatization

Tropical plants grown in full sun have leaves (sun leaves) which are structurally different from the leaves of plants grown in shade (shade leaves). Sun leaves have fewer chloroplasts, and thus less chlorophyll. Their chloroplasts are located deep inside the leaves and the leaves are thick, small, and large in number. Shade leaves have greater numbers of chloroplasts and thus more chlorophyll, are thin, large, and few in number. When plants are grown in strong light, they develop sun leaves which are photosynthetically very inefficient. If these same plants are placed in low light, they must either remake existing sun leaves or drop their sun leaves and grow a new set of shade leaves which are photosynthetically more efficient. To reduce the shock which occurs when a plant with sun leaves is placed in shade, gradually reduce the light levels it is exposed to. This process is called acclimatization. The gardener should acclimatize plants when placing them outdoors in summer by gradually increasing light intensities, and reverse the process before plants are brought indoors in the fall. For newly purchased plants grown in high-light conditions, acclimatize them by initially locating them in a high-light (southern exposure) area of your home and gradually moving them to their permanent, darker location over a period of 4 to 8 weeks.

Factors Affecting Plant Growth Indoors

Light, water, temperature, humidity, ventilation, fertilization, and soil are chief factors affecting plant growth, and any one of these factors in incorrect quantity will prevent proper plant growth indoors.

Light

Light is probably the most essential factor for indoor plant growth because they use this energy source to photosynthesize. When examining light levels for tropical plants, consider three aspects of light: intensity, duration, and quality.

Light intensity influences the manufacture of plant food, stem length, leaf color, and flowering. A geranium grown in low light tends to be spindly and the leaves light green in color. A similar plant grown in very bright light would tend to be shorter, better branched, and have larger, dark green leaves. Indoor plants can be classified according to their light needs by high, medium, and low light requirements. The intensity of light a plant receives indoors depends upon the nearness of the light source to the plant (light intensity decreases rapidly when moved away from the source of light). The direction the windows in your home face will affect the intensity of natural sunlight that plants receive. Southern exposures have the most intense light, eastern and western exposures receive about 60% of the intensity of southern exposures, and northern exposures receive 20% of a southern exposure. A southern exposure is the warmest, a western exposure is warmer than eastern as it receives the warm afternoon sun, and a northern exposure is the coolest. Other factors which can influence the intensity of light penetrating a window are the presence of curtains, trees outside the window, weather, seasons of the year, shade from other buildings, and the cleanliness of the window. Reflective (light-colored) surfaces inside the home/office will increase the intensity of light available to plants. Dark surfaces will decrease light intensity. Excessive dust on leaves can decrease light intensity reaching the leaves.

Day-length or duration of light received by plants is also of some importance, but generally only to those plants which are photosensitive. Poinsettia, kalanchoe, and Christmas cactus bud and flower only when day-length is short (11 hours of daylight or less). Most flowering indoor plants are indifferent to day-length. More information on this topic can be found in the “Environmental Factors Affecting Plant Growth” section in Chapter 1: Botany.

Low light intensity can be compensated by increasing the time (duration) the plant is exposed to light, as long as the plant is not sensitive to day-length in its flowering response. Increased hours of lighting allow the plant to make sufficient food to survive and/or grow. However, plants require some period of darkness to develop properly, and thus should be illuminated for no more than 16 hours. Excessive light is as harmful as too little light. When a plant gets too much direct light, the leaves become pale, sometimes burn, turn brown, and die. Therefore, during the summer months, protect plants from too much direct sunlight.

Light quality is the third aspect that should be taken into consideration with indoor plants. Light quality refers to the spectral distribution of light, or the number of different colored photons emitted by the light source (for example, blues, reds, greens). Additional lighting may be supplied by either incandescent or fluorescent lights. Incandescent lights produce a great deal of heat and are not very efficient users of electricity. If artificial lights are to be used as the only source of light for growing plants, the quality of light (wavelength) must be considered. For photosynthesis, plants require mostly blues and reds, but for flowering, infrared light is also needed. Incandescent lights produce mostly red and some infrared light, but are very low in blues. Fluorescent lights vary according to the phosphorus used by the manufacturer. Cool-white lights produce mostly blue light, and are low in red light. Foliage plants grow well under cool-white fluorescent lights, which are also cool enough to position quite close to plants. Blooming plants require extra infrared light which can be supplied by incandescent lights or special horticultural-type (fluorescent or LED) lights.

Water

Overwatering and underwatering account for a large percentage of tropical plant losses. The most common question gardeners ask is, “How often should I water my plants?” There is not a good answer to this question. Some plants like drier conditions than others. Differences in potting medium and environment influence water needs. Watering as soon as the soil crust dries can result in overwatering.

Plant roots are usually in the bottom 2/3 of the pot, so do not water until the bottom 2/3 starts to dry out slightly. You can’t tell this by looking at the plant. By the time the plant wilts or changes color due to lack of water, it has been damaged and will be less vigorous. You have to feel the soil. For a 6-inch pot, stick your index finger about 2 inches into the soil (approximately to the second joint of your finger). If the soil feels damp, don’t water. Keep repeating the test until the soil is barely moist at the 2-inch depth. For smaller pots, 1 inch into the soil is the proper depth to measure.

Water the pot until water runs out of the bottom. This serves two purposes. First, it washes out all the excess salts (fertilizer residue). Second, it guarantees that the bottom 2/3 of the pot, which contains most of the roots, receives sufficient water. However, don’t let the pot sit in the water that runs out. After a thorough watering, wait until the soil dries at the 2-inch depth before watering again. If the soil has become excessively dry and pulled away from the sides of the pot, it will be necessary to soak the container in the sink or other container until the soil is fully rehydrated and expanded. When testing for watering, pay attention to the soil. If your finger can’t penetrate 2 inches deep, the plant either needs a more porous soil mix or the plant is becoming root-bound.

Be aware of the temperature of the water. Cold water can stun or damage some tropical plants. Warm or room temperature water is best.

Temperature

Most house plants tolerate normal temperature fluctuations. In general, indoor foliage plants grow best between 70 and 80ºF during the day and from 60 to 68ºF at night. Most flowering indoor plants prefer the same daytime range but grow best at nighttime temperatures from 55 to 60ºF. The lower night temperature induces physiological recovery from moisture loss, intensifies flower color, and prolongs flower life. Excessively low or high temperatures may cause plant failures, stop growth, or cause spindly appearance and foliage damage or drop. A cooler temperature at night is actually more desirable for plant growth than higher temperatures. A good rule of thumb is to keep the night temperature 10 to 15º lower then the day temperature. When purchasing a new plant, check the label or do research on ideal temperature conditions. Some plants prefer cooler temperatures, while some need warm temperatures.

Humidity

Atmospheric humidity is expressed as a percentage of the moisture saturation of air. When humidity is too low, brown tips and margins may appear on tropical plant leaves. To provide increased humidity, attach a humidifier to the heating or ventilating system in the home, or place gravel trays (in which an even water level is maintained) under the plant containers. This will increase the relative humidity in the vicinity of the containers. As the moisture around the pebbles evaporates, the relative humidity is raised. Make sure the bottom of the pot does not come in contact with the water in the pebble tray, as it could soak up too much water and damage the plant roots.

Another way to raise humidity is to group plants close together. Some people spray a fine mist on the foliage, however, this is of doubtful effectiveness for total humidity modification unless repeated frequently throughout the day. Time this so that the plants will be dry by night. This lessens the chance of disease, since cool dampness at night provides an ideal environment for disease.

Fertilization

Indoor plants, like most other plants, need fertilizers containing three major plant food elements: nitrogen (N), phosphorus (P), and potassium (K). They are available in many different combinations and under a multitude of brand names. Each brand should be analyzed on the label, indicating specifically how much water-soluble elemental nitrogen, phosphate, or potash is available in every pound of the product. The three numbers on a package of fertilizer, such as 20-5-20, indicate the percentages (by weight) of nitrogen, phosphorus, and potassium, respectively, in the fertilizer product. Commercial fertilizers used for indoor plants are sold in granular, crystalline, liquid, or tablet forms. Each should be used according to instructions on the package label. Frequency of fertilizer application varies somewhat with the vigor of growth and age of each plant. Some need it every 2 weeks, while others will flower well for several months without needing any supplement. As a general rule, fertilize every 2 weeks from March to September. During the winter months, no fertilizer is needed because reduced light and temperature result in reduced growth. Fertilizing at this time could be detrimental to some plants.

Soluble Salts

Reduced growth, brown leaf-tips, dropping of lower leaves, small new growth, dead root-tips, and wilting are all signs of high soluble salts. These salts will accumulate on top of the soil forming a yellow to white crust. A ring of salt deposits may be formed around the pot at the soil line or around the drainage hole. Salts will also build up on the outside of clay pots, but is generally not harmful.

Soluble salts are minerals dissolved in water. Fertilizer dissolved in water becomes a soluble salt. When water evaporates from the soil, the minerals or salts stay behind. As the salts in the soil become more and more concentrated, plants find it harder and harder to take up water. If salts build to an extremely high level, water can be taken out of the root-tips, causing them to die.

High soluble salts damage the roots directly, and because the plant is weakened, it is more susceptible to attack from insects and diseases. One of the most common problems associated with high salt levels is root rot.

The best way to prevent soluble salt injury is to stop the salts from building up. Water correctly. When you water, allow some water to drain through, and then empty the drip plate. Water equal to 1/10 the volume of the pot should drain through each time you water. Do not allow the pot to sit in the water! If you allow the drained water to be absorbed by the soil, the salts that were washed out are taken back into the soil. Salts can be reabsorbed through the drainage hole or directly through a clay pot.

Plants should be leached every 4 to 6 months. Leach a plant before fertilizing so that the fertilizer does not wash away. Water the soil thoroughly as usual. Then, after about five minutes, water again, letting excess water flow out the bottom drain holes. The first watering dissolves the fertilizer salts. The second washes the salt out of the soil. If a layer of salts has formed a crust on top of the soil, you should remove the salt crust before you begin to leach. Do not remove more than 1/4 inch of soil. It is best not to add more soil to the top of the pot. If the soluble salt level is extremely high or the pot has no drainage, repot the plant.

The level of salts that will cause injury varies with the type of plant and how it is being grown. A plant grown in the home may be injured by salts at concentrations of 200 ppm. The same plant growing in a greenhouse, where the light and drainage are good, will grow with salts at 10 times that level, or 2000 ppm. Some nurseries and plant shops leach plants to remove excess salts before the plant is sold. Consider leaching newly purchased plants the first time you water them.

Growing Media

The potting soil or medium in which a plant grows, must be of good quality. It should be porous for root aeration and drainage, but also capable of water and nutrient retention. Most commercially prepared mixes are termed soil-less, which means they contain no soil. High-quality artificial mixes generally contain slow-release fertilizers, which take care of a plant’s nutritional requirements for several months. You can also prepare your own soil-less mix.

Preparing Soil-less Mixes

Soil-less mixtures can be prepared with a minimum of difficulty. Most mixes contain a combination of organic matter, such as peat moss or ground pine bark, and an inorganic material, like washed sand, vermiculite, or perlite. Materials commonly used for indoor plants are the peat-lite mixtures, consisting of peat moss and either vermiculite or perlite. The following are the most common media components.

Peat moss is readily available baled or bagged; sphagnum peat moss is recommended. Such materials as Michigan peat, peat humus, and native peat are usually too decomposed to provide necessary structural and drainage characteristics. Most sphagnum peat moss is acid in reaction with a pH ranging from 4.0 to 5.0. It usually has a very low fertility level. Sphagnum peat moss is mined, creating concerns about environmental damage, while coconut coir is readily renewable and environmentally friendlier than peat moss. Coir is a pH-neutral, non-hydrophobic soil amendment that aerates and improves water retention of soil.

Vermiculite is a sterile, lightweight, mica product. When mica is heated to approximately 1800ºF, its plate-like structure expands. Vermiculite will hold large quantities of air, water, and nutrients needed for plant growth. Its pH is usually in the 6.5 to 7.2 range. Vermiculite is available in four particle sizes. For horticultural mixes, sizes 2 or 3 are generally used. If at all possible, the larger-sized particles should be used, since they give much better soil aeration. Vermiculite is available under a variety of trade names. Vermiculite collapses with time and loses its positive characteristics.

Perlite is a sterile material produced by heating volcanic rock to approximately 1800ºF. The result is a very lightweight, porous material that is white in color. Its principal value in soil mixtures is aeration. It does not hold water and nutrients as well as vermiculite. The pH is usually between 7.0 and 7.5. Perlite can cause fluoride burn on some foliage plants, usually on the tips of the leaves. The burn progresses from the tip up into the leaf. Fluoride burns can be prevented by adding 1 1/2 times the recommended amount of lime when mixing the soil. Artificial mixtures are usually very low in trace or minor elements, therefore, it is important to use a fertilizer that contains these trace elements. A good formula for artificial mix (makes 3 bushels of media) follows.

• 1 bushel shredded coconut coir or peat moss
• 2 bushels perlite or vermiculite
• 1/2 cup finely ground agricultural lime
• 1/3 cup 20% superphosphate
• 1/2 cup 8-8-8 or similar analysis mixed fertilizer
• 1 level teaspoon chelated iron

Soil Mixes for Specific Plants

Soils must have the most efficient composition for the type of plant to be grown. We can divide indoor plant soils into four distinct groups, according to the type of plant to which they are most suited.

Artificial soil mixes work well but a mixture with soil could be used. Any soil containing garden loam should be pasteurized. This can be done easily at home. Spread the soil on a cookie tray and bake it at 180ºF for 30 minutes. Do not heat it longer than 30 minutes, and be aware that it will smell unpleasant while baking.

Foliage Plants: This soil should be moderately rich, have a good base of clay loam, and hold moisture and fertility adequately. It must be a crumbly, well-textured soil. It is generally made up of one part of good garden loam, one part of clean sand or perlite, and half to one part of either peat moss, compost, leaf mold, or vermiculite. Mixing about 1 teaspoon of superphosphate with each quart of mixed potting soil is desirable and encourages good root growth after repotting. If the garden soil is alkaline, sphagnum peat moss will have enough acid reaction to neutralize the mixture. This soil is used for all foliage plants and some flowering plants that do not prefer a rich soil.

Flowering House Plants: This soil is often referred to as humus soil because it contains about 50% humus-rich materials or similar ingredients. It is important that the soil does not become so rich that it is soggy after watering. Two parts of sphagnum, or one part sphagnum and one part vermiculite, are added to one part garden loam and one part clean sand. Also add 1 teaspoon of superphosphate per quart of soil mixture. This soil is generally used for African violets, gloxinias, begonias, calla lilies, and other tropical flowering plants.

Cacti and Succulents: This soil does not need any humus material. It is composed of equal parts of sand, garden soil, and vermiculite or perlite. It is preferred for cacti and other fleshy leaved, desert-type succulents.

Orchids: Fir-tree bark or Osmunda fiber is generally used in glazed or plastic pots. The container should be large enough so that new growth is 1-2 inches from the rim of container. Broken clay pieces can make up the lower inch in the container.

Containers

There are many types of containers from which to choose. A good container should be large enough to provide room for soil and roots, have sufficient room above the soil line for proper watering, provide bottom drainage, and be attractive without competing with the plant it holds. Containers may be made from ceramics, plastic, fiberglass, wood, aluminum, copper, brass, and many other materials.

Clay and Ceramic Containers

Unglazed and glazed porous clay pots with drainage holes are widely used. Ornate containers are often nothing but an outer shell to cover the plain clay or plastic pot. Clay pots absorb and lose moisture through their walls. Frequently the greatest accumulation of roots is next to the walls of the clay pot because moisture and nutrients accumulate in the clay pores. Although easily broken, clay pots provide excellent aeration for plant roots and are considered by some to be the healthiest type of container for a plant.

Ceramic pots are usually glazed on the outside, sometimes also on the inside. They are frequently designed without drainage holes. This necessitates careful watering practices and does not allow for leaching. Small novelty containers have little room for soil and roots and are largely ornamental. They should be avoided. It should be noted that putting pot chips, clay pot shards or gravel in the bottom of a pot does not improve soil drainage; they only provide a small space beneath the soil where some excess water can drain inside the pot.

Plastic and Fiberglass Containers

Plastic and fiberglass containers are usually quite light and easy to handle. They have become popular in recent years because they are relatively inexpensive and often quite attractive in shape and color. Plastic pots are easy to sterilize or clean for reuse, and because they are not porous, they need less frequent watering and tend to accumulate fewer salts.

Repotting

Actively growing indoor plants need repotting from time to time. This occurs very rarely with some slower-growing plants, more frequently with others. Foliage plants require repotting when their roots have filled the pot and are growing out the bottom holes. It is useful to know that certain species actually prefer to be pot-bound, such as African violets, aloe, and jade plant.

When repotting becomes necessary, it should be done without delay. The pot selected for repotting should be no more than 2 inches larger in diameter than the plant’s current pot, should have at least one drainage hole, may be either clay, ceramic, or plastic, and must be clean. Wash soluble salts from clay pots with water and a scrub brush, and wash all pots in a solution of 1 part liquid bleach to 9 parts water.

Potting media should be coarse enough to allow good drainage, yet have sufficient water retention capabilities. Most plants are removed easily from their pot if the pot is held upside-down while knocking the lip of the container sharply upon the edge of a table. Hold your hand over the soil, straddling the plant between the fore and middle fingers while knocking it out of its present container. Do not pull the plant out of the container.

Potting media should be moistened before repotting begins. To repot, place soil in bottom of pot. If the plant has become root-bound it will be necessary to cut and unwind any roots that circle the plant, otherwise the roots will never develop normally. If the old soil surface has accumulated salts, the top inch should be removed. Set the rootball in the middle of the new soil. Fill soil around the sides between the rootball and pot. Do not add soil above the original level on the rootball, unless the roots are exposed or it has been necessary to remove some of the surface soil. Do not pack the soil as this decreases aeration. To firm or settle it, tap the pot on a level surface or gently press the soil with your fingers. After watering and settling, the soil level should be sufficiently below the level of the pot to leave an inch or more headroom.

Headroom is the space between the soil level and the top of the pot that allows for watering a plant. A properly potted plant has enough headroom to allow water to wash through the soil to thoroughly moisten it.

Large indoor trees may require assistance to safely remove the plant from the pot. It should not be pulled out by the trunk or branches. It is easier to remove if the soil is moist. If the tree is root bound or has roots growing through the drain hole, the pot may have to be broken to avoid damaging the roots. It is often best to repot a large plant outdoors in warm weather.

Training and Grooming

Pinching is the removal of 1 inch or less of new stem and leaf growth, just above a node. This leaves the plant attractive and stimulates new growth. It can be a one-time or continuous activity, depending on the needs of the plant. If a plant should be kept compact but well-filled out, frequent pinching will achieve this.

Pruning is a similar activity. Pruning includes removal of other than terminal shoot tips. Sometimes an entire branch or section of a plant should be removed for the sake of appearance.

Disbudding is another related care activity. Certain flower buds are removed either to obtain larger blooms from a few choice buds or to prevent flowering of a very young plant (or recently rooted cutting) that should not bear the physical drain of flowering early.

Ivies and hoya, as well as philodendron and syngonium, can be easily trained on trellises.

It is important to keep plants clean and neat. It not only improves the appearance of plants but reduces the incidence of insects and disease problems. Remove all spent flowers, dying leaves, and dead branches. Keep leaves dust-free by washing plants with warm water and mild soap (cover pot to prevent soap from entering the soil). Dust can clog stomata and reduce respiration. If tips of leaves become brown and dry, trim them off neatly with sharp scissors.

Common Indoor Plant Pests

Indoor plants may still be exposed to potential plant pests. It is important to inspect for pests prior to purchasing plants to ensure that you are buying a healthy plant and to prevent possible infestation of any other indoor plants you may have at home. It is also important to inspect plants that you may have kept outside during the summer months. Here we will describe some of the common indoor plant pests you may see and different pest control options. Please remember to read any pesticide labels to assure you are using the appropriate product for your plant, pest, and environment.

Table 12-1: Common Indoor Plant Pests

Troubleshooting Indoor Plant Problems

Do your plants look unhealthy? Are you unsure of what might be the cause of your plant’s condition? Below, we provide some signs of common indoor plant problems unrelated to plant disease and the potential treatments for these issues.

Table 12-2: Troubleshooting Common Indoor Plant Problems

Care of Specific Plants

There are a number of wonderful house plants currently available for gardeners of all skill levels. When making the decision what plant is best for your space, choose plants that fit the light duration, light intensity, and temperature levels your house can provide. You should also consider growing what you enjoy having in your home, house plants are as much about beauty and enjoyment as they are about the health benefits they provide. Indoor plants can be a wonderful addition to any room and with the diversity of plants available through local plant nurseries and online, you will certainly be able to find a plant that fits your needs. The following are a few of the broad categories of houseplants that you may encounter:

Bulbous Plants

Just like bulbs are planted outside for beautiful seasonal blooms, they can also be grown indoors. The constant temperatures and control over the environment allows for varieties to be grown that may not survive many outdoor conditions. Bulbous plants are generally grown for their beautiful blooms.

Additional information can be found here: VCE Publication “Forcing Flower Bulbs for Indoor Bloom” HORT-67NP, Cornell Extension publication “Bulbous Plants for Indoor Bloom” and University of Minnesota Extension “Growing bulbs indoors”

Trailing and Climbing

Trailing and climbing plants can add a wonderful dimension to any indoor plant collection. They can be trained to grow on different support structures within the home or as set in the pot where they are planted. There are many varieties of climbing and trailing plants, so ensure that you know what your specific plant needs to thrive in an indoor environment. For example, some ivies are able to thrive under fluorescent lights in an office environment, where other vining plants may not be able to do so successfully. Trailing and climbing indoors plants are often grown for their foliage and shape.

Additional information on ivy: Clemson Cooperative Extension “Growing English Ivy Indoors”

Ferns

There are a number of ferns that can successfully grow indoors under the correct conditions. Humidity, temperature, and light are all important factors for ferns and a fern that doesn’t receive exactly what it needs will not grow well in its indoor setting. Fiddlehead and staghorn ferns are two popular varieties that can add a great deal of interest to the home. Additional information on ferns: University of Georgia Cooperative Extension “Growing Ferns”

Flowering Plants

Bringing beautiful blooms inside can be a rewarding experience and there are many flowering plants well adapted to growing indoors. As with other types of plants, be sure to understand the requirements for your plant. Some may need periods of darkness, cool temperatures, additional artificial light, or more in order to bloom indoors. However, when those needs are met you are granted with a colorful and exciting addition to your home!

Additional information on specific flowering plants can be found here: University of Missouri Extension “Care of Flowering Potted Plants”

Foliage Plants

Many indoor plants are grown solely for their interesting leaves. Whether you’d like to grow plants for unique colors, shapes, sizes, or patterns, there are indoor foliage plants that will fit your interests.

For more on easy to grow foliage plants: New Hampshire Extension “Which foliage houseplants are easiest to grow?”

Succulents

A succulent describes a type of plant that stores water in its stems and leaves. There are hundreds of plants that fall into this category of all shapes, colors, and sizes. Succulents can be hardy and able to survive outdoors in colder climates, or soft. Soft succulents are those that need consistent temperatures and are the ones that thrive in indoor environments when properly maintained. Succulents require regular watering once the soil has dried and should be placed in bright direct or indirect sunlight. Cacti are one large category of succulents often available for indoor growing.

More information here: Iowa State University Extension and Outreach “Care of Succulents Indoors”

Trees and Tree-Like Plants

Indoor trees and plants that have been trained to take a tree-like form can add a lot to an indoor space. Not only can some citrus fruits grow indoors, sharing their fruits for your kitchen, but they also offer the height and mass that many indoor plants aren’t able to offer. A tree can fully fill a space and adds interest to a room.

For information on growing citrus indoors: University of Minnesota Extension “Growing Citrus Indoors”

Indoor Plants and Toxicity for Pets

By Marion Ehrich and Dennis Blodgett, Virginia Maryland College of Veterinary Medicine, Virginia Tech

Family pets can be poisoned by a number of different toxic plants found inside the home or outside in the home garden. Lists are long, for example the ASPCA (American Society for Prevention of Cruelty to Animals) Animal Poison Control Center lists over 400 plants that can be toxic to dogs and cats. A full list of these toxic plants is available here. Another good source of information is your local veterinarian.

Veterinarians and other health professionals are often called about poisonous plants because plant poisonings are on rule-out lists for many different pet disorders. Most plant poisonings are not life-threatening, but anything eaten, even non-toxic plants, can cause gastrointestinal disturbances such as vomiting. Dogs are notorious for indiscriminate eating. Cats are more fastidious, but may ingest toxic houseplants and end up with minor to life threatening clinical signs. Certain common houseplants belonging to the Araceae family can release insoluble calcium oxalate crystals. These include dieffenbachia, philodendron, pothos (pictured), in addition to Calla lily and Peace lily. These crystals cause mouth and gastrointestinal irritation almost immediately, can be painful, and can last from hours to days. Contact with a local veterinarian should be considered.

Terrariums and Dish Gardens

Terrariums

A terrarium is a “miniature garden” in which plants are often contained within a tightly closed glass or clear plastic vessel, usually with a moveable top and requiring very little attention. Because such containers are kept closed most of the time, air inside stays at high humidity, similar to a greenhouse. This is an ideal environment for a variety of houseplants. Condensate eventually forms on the inside of the container and is returned to the medium as water, which may preclude the addition of water for several weeks. Overwatering is one of the most common problems in terrarium care – medium should be kept moist, not wet. If conditions inside become too moist, the top should be removed to evaporate excess water. A standard medium, along with a sand and/or gravel base for drainage and charcoal to absorb unpleasant odors are commonly used. Fertilizer applications are made only to sustain plants and when in use should be in soluble dilute form. The terrarium should be placed in bright, but not direct sunlight at average room temperatures.

Dish Gardens

Desert dish gardens can be made by planting various arid type cacti and other succulents together in a decorative dish container. Open, shallow dishes are the best choices for containers. Choose the soil based on the type of plant being grown.

Table 12-3: Light requirements for selected indoor plants

Plant Lists

Cool Temperature Plants

Medium Temperature Plants

High Temperature Plants

Plants for Specific Indoor Gardening Uses

Plants that will grow in water

Plants that withstand adverse house conditions

Plants well-suited as large container decorative specimens

Plants that perform well under average home conditions

Low, creeping plants for groundcovers in interior plant boxes

Vines and trailing plants for totem poles and trained plants

Plants suitable for hanging baskets

Plants suitable for desert dish gardens

Plants suitable for tropical terrariums

Attributions

• Courtney Soria, Loudoun County Extension Master Gardener (2021 reviser)
• Nancy Butler, Hanover Extension Master Gardener (2021 reviser)
• Melanie Smith, Hanover Extension Master Gardener (2021 reviser)
• Meredith Hoggatt, Extension Agent, Agriculture and Natural Resources (Author of “Common Indoor Plant Pests,” 2022)
• Lisa Sanderson, Extension Agent, Agriculture and Natural Resources (2015 reviser)
• Megan Tierney, Extension Agent, Agriculture and Natural Resources (2015 reviser)
• Stephanie Huckestein, Education and Outreach Coordinator, Hahn Horticulture Garden, Virginia Tech (2015 reviewer)
• Diane Relf, Extension Specialist, Horticulture (2009 reviser)

Image Attributions

• Figure 12-1: Black root rot. Image 5427727 by Cheryl Kaiser, University of Kentucky, Bugwood.org. CC BY-NC 3.0 US
• Figure 12-2: Peat moss. Johnson, Devon. 2022. CC BY-NC-SA 4.0.
• Figure 12-3: Pot bound plant. Reed, Kathleen. 2022. CC BY-NC-SA 4.0.
• Figure 12-4: Steps in repotting. Reed, Kathleen and Johnson, Devon. 2022. CC BY-NC-SA 4.0.
• Figure 12-5: Pinching plants leaves them more attractive and stimulates new growth. Grey, Kindred. 2022. CC BY-NC-SA 4.0.
• Figure 12-6: Amaryllis. “Amaryllis.” 2013. Hige, Aka. Flickr. CC By-SA 2.0.
• Figure 12-7: Dieffenbachia. “Dieffenbachia houseplant” Aj West. 2017. Wikimedia. CC BY-NC-SA 4.0.
• Figure 12-8: Terrarium. “Succulent Plant Terrarium.” Fraxinus.ornus. 2013. Wikimedia. CC BY-SA 4.0.
• Figure 12-9: Dish Garden. “Succulent Dish Garden – Lisa Greene, AAF, AIFD, PFCI.” 2012. Flower Factor. Flickr. CC BY-NC 2.0.