Growing houseplants successfully (2023)

Bodie V. Pennisi, specialist in floriculture

• introduction
• Factors affecting plant growth
• Licht
• Temperature
• Relative humidity
• water
• nutrition
• soil/growth medium
• What to look out for when buying houseplants
• select containers
• Pruning, maintenance, cleaning and repotting
• pest control
• What to do with plant problems?
• Summary of cultural maintenance
• bibliography

introduction

Much of nature's scenic beauty has been replaced by densely populated areas that sprawl for miles from urban centers. This visual pollution affects us all and leaves us longing for a closer connection with nature. We spend about 90 percent of our time indoors. Houseplants are an ideal way to create attractive and restful environments while enhancing our well-being. In addition, houseplants can be a satisfying hobby and help purify the air in our homes. Indoor plants not only convert carbon dioxide into oxygen, but also bind and absorb many pollutants. Many of these chemical compounds, which are released into our air through a process called "outgassing," come from everyday objects found in our homes and offices.

To be a successful indoor gardener, you need to understand how the indoor environment affects plant growth and how growing it differs from growing plants outdoors.

Factors affecting plant growth

Plant growth is affected by light, temperature, humidity, water, nutrition and soil.

Licht

Of all the factors affecting plant growth indoors, adequate light is by far the most important. Light is needed for plants to produce food and survive - in general, the more light there is, the more food is produced for growth. Light is measured in units called foot candles. A foot candle (ft-c) is the amount of light a candle casts on a white surface at a distance of 1 foot in a completely dark room. Outdoors, light levels on a bright day range from 10,000 ft-c in an open, sunny area to 250 ft-c or less in the shade of a large tree.

It is very helpful to have a general idea of ​​how much light there is in a specific place in your home. You can get a pretty good estimate with a handheld light meter, or you can use a 35mm camera and do the following:

• Set the film speed indicator to ASA 25 and the shutter speed to 1/60 second.
• Place a piece of white paper where you want to measure the light levels, point the camera close enough to the paper to fill the view, and set the aperture so the meter shows correct exposure.
• Read the approximate luminous intensity from Table 1.

With the help of this table you can read the light intensity from anywhere in your home. For example, if the f/stop setting is f/16, the approximate speed is 2,400 ft-c.

Based on light readings, your home can be divided into four areas that have the following light levels for 8 hours per day:

1. Dimly lit areas: 25 ft-c - 75 ft-c
2. Medium light areas: 75 ft-c - 200 ft-c
3. Bright Areas: above 200 ft-c but no direct sunlight
4. Sunny light areas: at least 4 hours of direct sunlight

In your home, the amount of light in a given location is variable – it is influenced by the presence of trees outside (may give shade at certain times), roof overhangs (may give shade at certain times), wall color (reflectance), window curtains, day length, time of day and season.

When purchasing houseplants, choose plants for a specific location based on the approximate light levels at the location. The plant's label usually contains information about the plant's light requirements. If the plant label lists "high light" but the selected area in the home does not provide adequate light, artificial light sources such as fluorescent lighting and/or special incandescent lighting can be used to supplement the natural light.

It may also help to increase the number of hours of light exposure - for example 16 hours light and 8 hours dark. This increases the number of hours that plants receive light.

While sufficient light is crucial for plant growth, too much light can be harmful (Figure 1).

Houseplants are classified according to the amount of light needed for growth. (See Table 3 for a list of plants and their light requirements.) Look for this information in general terms on the plant's label:

• Low: at least 25 ft-c - 75 ft-c, 75 ft-c - 200 ft-c for good growth
• Medium: minimum 75 ft-c – 150 ft-c, 200 ft-c – 500 ft-c preferred
• High: minimum 150 ft-c – 1,000 ft-c, 500 ft-c – 1,000 ft-c preferred
• Very high: at least 1,000 ft-c, preferably 1,000+ ft-c

East-facing windows within the home generally provide the best light and temperature conditions for most houseplants to grow, as the plants receive direct morning light from sunrise until almost noon. Footcandle readings on these windows can reach 5,000-8,000. In the course of the morning, the direct sun recedes from the room.

An east room is cooler than south or west rooms because the house absorbs less radiant heat. The light from the east is cooler than that from the south or west and therefore causes less water loss from the plants.

South-facing windows offer the greatest variation in light and temperature conditions. The low winter sun shines across the room for most of the daylight hours.

In summer, when the sun is further north than in winter, the sun rises at an acute angle in the morning and is high in the sky at noon. Direct light falls into a south-facing window only at noon. If the windows cantilever outwards, the sun may not penetrate the room at all. The midday sun on a summer day can measure 10,000 ft-c. Indoors, however, a south-facing window with a wide eaves on the outside receives about the same amount of light as a north-facing window. Southern and western exposures are interchangeable for most plants. In winter, most plants, except those that clearly prefer a north orientation, can be placed in a south-facing room.

North-facing windows offer the least light and the lowest temperature. Because the United States is in the northern hemisphere, it gets most of its sunlight from the south. Of the four exposures, the northern exposure receives the least light and heat all year round.

Due to low light levels, maintaining healthy plants can be a challenge. A north windowsill can see light levels up to 200 ft-c on a clear winter day, which is optimal for some plants like the African violet. This exposure is best for plants with green foliage, as coloration on variegated foliage tends to fade in low light. Although most plants grown indoors won't grow in a northern space, they can tolerate it for short periods of time.

The seasons change the amount of natural light entering through windows. For example, the summer sun reaches a higher zenith compared to the winter sun (Figure 2). Therefore, sunlight penetrates further into a room in winter.

How can you tell if your plant isn't getting enough light?

• The plant does not grow.
• The internodes (spaces between the leaves) of the new growth are much longer than the internodes of the older part of the plant.
• The new leaves are smaller than the older leaves.
• Leaf color is lighter green on the newer leaves than on the older leaves.
• The older leaves have died.

Temperature

Temperature is the second most important factor affecting indoor plant growth. Humans are comfortable in the 72 degrees F to 82 degrees F range, and houseplants can tolerate and grow well in the 58 degrees F to 86 degrees F range since most houseplants are native to tropical and subtropical areas of the world.

Temperature and light are linked through the processes of photosynthesis and respiration. These processes can be thought of as the "yin and yang" of plant life - two parts of a circle. Photosynthesis builds sugars and starches, which are then broken down through respiration to provide energy for the development of new tissues (growth) and the maintenance of existing tissues. High temperature accelerates breathing. If the plant isn't producing enough sugars (like in low light), high temperatures can break down what few sugars are being made, leaving little to none for growth. maintenance before growth; Therefore, with insufficient light, plants will not grow. If the light is so low that the sugars produced are insufficient for maintenance, the plant will eventually die.

When sugar levels are low, the plant absorbs nutrients and sugars from older leaves to grow new leaves. To help plants indoors, two options are available: (1) increase light levels to increase photosynthesis and sugar production, or (2) lower nighttime temperatures to slow respiratory rates and increase sugars for growth allow.

What temperatures can occur in apartments? During the summer it can happen that the air conditioning has been turned off at night or the thermostat settings have been increased at the weekend, resulting in higher than desired night-time temperatures. During winter, heaters turned off at night or thermostat settings that are too low at weekends can result in lower night-time temperatures. Take extra care to ensure temperatures don't drop below 50 degrees F or cold damage will develop on some sensitive foliage plants (e.g. Chinese Evergreen, Aglaonema). Cold damage is manifested by yellowing of the lower leaves and/or defoliation.

Plants differ in their minimum and maximum temperature requirements. Examples of cool-loving plants suitable for locations where temperatures drop to the low 50s at night and into the 60s during the day include Cyclamen, Wonder Plant, Fatshedera, Japanese Aralia, and Fatsia. A list of plants and their temperature requirements can be found inTisch 3.

Not all houseplants have the same temperature requirements for optimal growth. For example, cast iron plant, aspidistra, and ferns actually grow better in cooler temperatures (72°F), while other tropical plants grow best when temperatures are 90°F - 95°F. Such temperatures are rarely allowed indoors.

The best temperature range for houseplants is 70°F - 80°F during the day and 65°F - 70°F at night.

Relative humidity

Relative humidity is the amount of moisture contained in the air. For indoor plants, relative humidity below 20 percent is considered low, 40 to 50 percent is considered medium, and above 50 percent is considered high. Relative humidity is a very important factor, but one that is easily overlooked. In a greenhouse, the relative humidity is 50 percent or more. Exposing newly purchased plants to the 10 to 20 percent relative humidity typical of most homes can result in rapid transpiration and water loss (Figure 3). Most houseplants come from the tropics, where high relative humidity is common. So, follow these steps to help your plants adjust to the low relative humidity in your home.

• Place plants close together to create a microenvironment with a higher relative humidity.
• Use a shallow container filled with water and lava rocks or gravel, which provides evaporation from a large surface area and increases relative humidity.
• Use a humidifier.
• Use mist bottles to spray water around the plant; In reality, however, you would have to spray every few minutes for an indefinite period of time to see a difference in the relative humidity around the plant.
• Leaves and flowers of plants with hairy leaves should not be sprayed with water. The water on such leaves can stay longer, providing an opportunity for disease spores to germinate.

water

amount of water

Learning to water is one of the most important skills in plant care. Applying too much water can suffocate plant roots and too little water leads to erratic and stunted growth. The frequency of watering depends on the conditions in which the plants grow. When considering how much water to apply, consider the following:

• Plant Type: For a list of plants and their moisture requirements, seeTisch 3. Not all plants are equal in their water needs. This information, along with light preference, is usually included on the plant label. For example, a croton that prefers lots of light will likely need more frequent watering than a succulent like the opuntia cactus. Both have similar light needs but different water requirements.
• Plant Size: Larger plants need more water compared to smaller plants.
• Container Volume: If the grow container is too small, it may need to be watered more frequently.
• Soil Moisture: The amount of water already in the growing medium will also affect your watering frequency.
• Light Intensity: Plants under strong light transpire more water than plants under low light.

Improper watering causes many problems. Containers with saucers can lead to an excessive accumulation of soluble salts (from the fertilizer applied). High levels of soluble salts can damage plant roots and impede growth. Discard any water that drained into the saucer after irrigation and apply large amounts of water to the soil to leach out the accumulated soluble salts. To decide when to water, feel the soil by pressing a finger about an inch below the surface. If the soil is still damp, no further water is needed. Water devices or water meters are also available to make watering easier.

water quality

Irrigation water quality is a problem for crops that are susceptible to fluorine and chlorine, such as B. Corn plant (dracaena), Ti plant (Cordyline), peacock plant (Maranta) and rattlesnake plant (Calathea) (Figure 4). Alleviate this problem by letting the water sit for a few days - to allow some chlorine and fluorine to release from it - before applying the water to the plants. Move susceptible plants away from the pool edge to prevent water splashes from reaching the foliage. Do not use susceptible plants near enclosed pools. In general, plants with long linear leaves (like the spider plant) are more susceptible to fluorine.

nutrition

Many indoor gardeners have the same problem with fertilizer as they have with water - they want to give their plants too much. The risk of over-fertilization arises because any fertilizer used, whether in liquid, powder or tablet form, will dissolve in soil water and form salts in the water. If you fertilize too much, the water in the soil becomes so salty that it 'burns' the plant's roots by depriving them of water (Figure 5). Excess soluble salts will collect as a whitish crust on the surface of the growing medium and/or near the rim of the container.

Before feeding plants, consider the following:

Plant type:Some plants are heavy feeders (e.g. Ficus species), while others require little or no additional fertilizer for months (e.g. succulents).
soil volume:The existing growing medium - smaller pots require less fertilizer compared to larger pots as they contain less soil.
Light intensity:The higher the light levels, the more nutrients are needed for plant growth.

A newly purchased, healthy plant rarely needs to be fertilized immediately. In most cases, the amount of fertilizer applied by the commercial manufacturer is sufficient for two to three months in the household. This rule is flexible - fertilization is desirable in the event of obvious deficiency symptoms.

The secret to fertilizing indoor plants is to apply small amounts of fertilizer as the plant grows. With no new growth, the plant has a limited need for more fertilizer. In winter, when light levels are low, a plant's need for fertilizer is reduced. In summer, when light levels increase and the plant is actively growing, the need for fertilizers increases. As a starting point, use about a quarter of the label rate for monthly applications. When the overall plant color turns a lighter green, fertilize every two weeks. If the new growth is dark green but the leaves are small and the internodes appear longer than the older growth, reduce the amount of fertilizer.

Different fertilizer formulations are available to the indoor gardener. Many fertilizers are available in specially formulated formulas for houseplants. In general, they contain a lower percentage of the required minerals to avoid over-feeding problems.

soil/growth medium

The growing medium provides anchorage, water and minerals. When repotting plants, make sure the new mix is ​​well-drained and aerated, holds water and nutrients well, and is in the correct pH range (5.0-6.5). Good potting soil provides the root system with plenty of oxygen. Most professional mixes are fine to use. Some plants require special mixtures, e.g. B. bromeliads, orchids and African violets. Either buy these mixes or make your own. Below are some formulas that can be used to make a homemade potting mix.

Cultivation mix for flowering indoor plants

The following potting mix will grow acceptable flowering plants in most homes for most gardeners:

• 1 part garden soil or potting soil
• 1 part sand or perlite or vermiculite
• 1 You have Peat Jam

Add 2 to 3 ounces of 20 percent superphosphate and 3/4 ounce of either bone meal or dolomite limestone (by weight) to 4 gallons of potting mix. After sterilizing the soil (see "To Sterilize the Soil"), add 3 tablespoons of a 6-6-6 or similarly balanced fertilizer for every 4 gallons (½ bushel) of the mix. Add a minor element formulation according to the manufacturer's recommendations.

Growing mixtures for green plants

Although most foliage plants will grow satisfactorily in the growing mix recommended for flowering houseplants, they will grow better if the mix contains a higher percentage of organic matter.

• 1 part garden soil or potting soil
• 1 part sand or 2 parts peat moss

OR

• 1 part pine bark
• 2 parts peat

OR

• 1 part sand
• 1 part pine bark
• 1 You have Peat Jam

Add 2 to 3 ounces (dry weight) of dolomite limestone to 4 gallons (½ bushel) of mixture. For fluoride-sensitive plants, adjust the pH so that it does not fall below pH 6.5. Superphosphate contains enough fluoride to cause leaf burns on sensitive plants. After sterilizing the soil, add 3 tablespoons of a 6-6-6 or other fertilizer like 5-10-5 to every ½ bushel. Plastic-coated fertilizers can also be used; Most of them require about 2 ounces per ½ bushel. Add a minor element formulation to the potting soil according to the manufacturer's recommendation.

Breeding mixtures for bromeliads

Bromeliads are plants native to Central and South America that are either epiphytic (they grow on branches or in the canopy of trees) or terrestrial (they grow in the ground). Although most bromeliads can be successfully grown in foliage plant mixes, most thrive better in specially designed soil mixes. Any bromeliad mix needs to be well aerated and drained.

• 2 Peat jam for you
• 1 part perlite
• 1 part for bark

OR

• 1 part peat
• 1 part pine bark

OR

• 1 part peat
• 1 part pine bark
• 1 part cypress shavings

Add 2 ounces of dolomitic limestone to 4 gallons (½ bushel) of soil mix and a minor element mix. Dissolve 1 ounce of water-soluble 10-10-10 fertilizer in 3 gallons of water. Use this solution after repotting and again monthly when watering. Also add enough water to fill the vase formed by the overlapping leaf bases.

Growing mixtures for orchids

Orchids have a lot in common with bromeliads, as they also grow as epiphytes on trees and as terrestrial dwellers on the ground. A mix for orchids should also have excellent drainage and aeration. Some soil mixes that can be used are:

• 3 parts Osmunda tree fern fiber (moisten before use by soaking in water for 12 hours)
• 1 part redwood bark

OR

• 5 parts for bark
• 1 part perlite

Tree fern sheets can also be used to grow epiphytic orchids. Add 1 ounce (dry weight) of dolomite limestone for every 4 gallons (½ bushel) of soil mix. Do not add fertilizer to the mix. After plants are potted, add ¼ ounce of liquid 10-10-10 with minors per gallon of water and fertilize once every 6 weeks (if plants are growing in Osmunda fern fiber). If plants are growing in fir bark, use a 30-10-10 liquid fertilizer with minor ingredients every 6 weeks instead of a 10-10-10 fertilizer.

Cultivation mix for succulents and cacti

Cacti and other succulents grow best in well-drained and aerated soil.

• 2 parts garden soil or potting soil
• 2 parts sand
• 2 parts peat
• 1 part perlite (shredded charcoal can be substituted)

Add 2 ounces (dry weight) dolomite limestone to 4 gallons (½ bushel) soil mix, 2 ounces (by weight) bone meal, and ½ ounce superphosphate. After sterilizing the soil, add a minor element additive according to the manufacturer's recommendations.

Growing mixture for ferns

Ferns grow well in most recommended mixes that are high in organic matter with good soil aeration and drainage properties. Use one of the suggested foliage plant mixes. However, most indoor ferns grow better in the following mix:

• 1 part garden soil or potting soil
• 1 You have Peat Jam
• 1 part pine bark
• 1 part coarse sand

Add 2 ounces (dry weight) of dolomitic limestone to each ½ bushel (4 gallons) of soil mix and ½ ounce of either bone meal or 20 percent superphosphate. After pasteurizing the soil mixture, add smaller elements to the mixture. Add 1 tablespoon of a 6-6-6 or similarly balanced fertilizer to every ½ bushel of soil mix.

Growing mixture for African violets

There are a variety of soil mixes for African violets, and most of them will produce high quality plants. A good mix should be well drained and aerated.

• 2 Peat jam for you
• 1 part vermiculite
• 1 part perlite

Add 2½ tablespoons of dolomite and 1½ tablespoons of 20 percent superphosphate to every ½ bushel of soil mix. Add 3 tablespoons of a high phosphorus fertilizer like 5-10-5 or a fertilizer in a similar ratio.

How to sterilize soil

Sterilization reduces the number of diseased organisms and weeds present in the soil. First mix the soil with an equal portion of vermiculite or peat moss (otherwise the soil will become very hard). Next, moisten the mixture and place in the oven. Let it "bake" at 180 degrees F-200 degrees F for 1 hour. Once the soil has cooled, it is ready to use. To treat soil in the microwave, first mix the portion with an equal amount of vermiculite or peat moss and moisten. Place the mixture in a plastic bag. Next, consult the manufacturer's manual to determine the amount of time and power level required to heat the bulk soil to about 180 degrees F (most soils generally take about 10 to 15 minutes). Insert a probe into the soil and make sure it is heated to 180 degrees F - 200 degrees F. Allow the soil to cool before using or storing for future use.

Make sure the soil or potting soil you plan to sterilize does not contain perlite. At high temperatures, toxic levels of fluoride can be released and damage your plants.

acclimatization

Acclimation is the adjustment of a plant to a new environment and is very important for the health and growth of houseplants. In greenhouses, plants are used to plenty of light, nutrients, water supply, temperatures and relative humidity - ideal conditions for rapid growth (Figure 6). Residential homes with dimly lit interiors and low relative humidity will most likely make plants stressful - the greater the difference between the previous environment and the home's surroundings, the greater the stress the plant will endure.

The acclimatization usually takes place in the greenhouse or in the nursery. Plants are grown in low light and with fewer nutrients for a period of time. Because this slows down plant growth, acclimated plants are not ready for market as early as non-acclimatized plants. Acclimated plants cost more than unacclimatized plants, but it's money well spent. Figure 7 and Table 2 describe the symptoms and appearance of acclimated plants.

To acclimate plants at home, place newly purchased plants in bright spots for at least 3 to 4 weeks, and then move them to their permanent location. Canopies and patios are ideal bright spots for your plants during the warm months, as long as the plants are not exposed to direct sunlight. The most common symptom experienced by indoor plants is defoliation. As long as it is not extensive and slows down after a few weeks, the plants will adapt to the location. However, remember that every time the plant is moved it goes through an acclimatization period and such changes can become obvious.

Find out as much as possible about the degree of acclimatization of the selected plants. The dealer should be able to provide this information. If you buy plants from a garden center, ask if the plants have been acclimated.

Remember that the most important factors in the growth of houseplants are adequate light, fertilizer and water in reduced amounts.

What to look out for when buying houseplants

Only buy healthy-looking plants with medium to dark green foliage (unless you want the foliage to be a different color).

Avoid plants with unnaturally mottled, yellow, or brown leaves. If the plant is unhealthy at the nursery, there is a chance it will die soon after consumer purchase. Look for pests on the underside of the leaves. Remove the plant from the pot and examine the root system. Healthy roots are and should generally be visible along the outside of the globe and have an earthy odor (Figure 8).

Any discoloration, generally brown or blackened roots, are signs of trouble. Some plants, like dracaenas, have roots of colors other than white. Unhealthy roots can also smell foul. When buying ferns, don't be alarmed if you see brown spots or long rows of structure on the lower leaf surface; These "spots" are reproductive structures called spores.

select containers

Planters can increase the decorative value of plants. When choosing a planter, consider the following:

• Suitability for the needs of the plant
• Suitability for the needs of the individual and the environment
• cost and availability
• strength and durability
• Drainage
• weight

The style, shape, and size of the container should complement the plants being grown. Small containers work best for small, slow-growing plants, while fast-growing plants work better in large containers.

Containers can be made from a variety of materials - terracotta, clay, plastic or ceramic. Fired clay terracotta pots are among the most popular options, with designs ranging from the simple to the ornate. Plants thrive very well in terracotta pots, as the porous surface allows good air exchange between the plant roots and the environment. Other clay containers (not considered terracotta) are gray to brown in color depending on the clay used. Clay pots can be glazed or unglazed. The glazed pots restrict the exchange of air, but offer more design options. Unglazed pots evaporate water more quickly and the plants in them may need more frequent watering. Disadvantages of clay containers include their weight (especially large pots) and the potential for them to chip or break.

Made from materials such as polyethylene, polyurethane, recycled plastic and fiberglass, plastic pots have gone from being very simple to being quite elaborate. They have the advantage of being lightweight and resistant to shattering and breaking. Air exchange and water evaporation are generally lower with plastic containers than with clay containers. Plants in plastic pots don't dry out as quickly as plants in clay pots, increasing the risk of overwatering.

There are generally two types of containers - those with drainage holes and those without. In containers with drainage holes, do not allow plants to sit in water-filled saucers unless the plant is hanging above the water level by a layer of rock. To avoid salt build-up, leach the soil once a month by applying a gallon of water to every cubic foot of potting soil; After a few hours, follow with ½ gallon of water. If the potting mix contains garden soil, apply 5 gallons of water per cubic foot of growing medium.

Containers without drainage holes work well for plants like the peace lily (Spathiphyllum), which need a lot of water, but they should not be used for cacti and succulents.

Pruning, maintenance, cleaning and repotting

When is the best time to cut? "When the knife is sharp" says an old proverb and means to orient oneself to the natural life cycles. For example, if the plant is growing rapidly and you want to maintain a certain size, prune lightly and frequently, removing shoots or shoot tips when they are small. Removing the very immature tips is called pinching. Pinching and light pruning will also increase stem branching, resulting in a sturdier, fuller plant.

Once the plant has outgrown its container, root pruning is advisable. Pull the roots away from the root mass, then cut back to within 1 inch of the soil mass. An alternate method is to make three or four vertical cuts 1 inch deep into the soil ball on opposite sides of the root ball.

If you reuse bins, make sure they're clean by washing out old compost, chemical or paint residue. Sterilize the container by soaking in a 10% bleach solution and rinsing well.

A clean plant is a healthy plant. Water flow causes salt to accumulate along leaf edges and/or tips, creating necrotic areas. Dust dulls normal leaf coloration, reduces plant value, but also shades plant surfaces and reflects light that can be used for photosynthesis. Dust on the lower leaf surfaces can clog stomata (specialized cells involved in water transpiration) and inhibit gas exchange within the leaf. Leaves with thick, shiny cuticles (croton, ficus, peace lily, bromeliads) should be cleaned with a damp sponge.

If the plant is small, dip the leaves in lukewarm water and toss them around. Water should not be used when cleaning cacti, African violet leaves, and other plants with hairy leaves. Instead, use a clean, small brush to remove dust. Remove dead flowers and leaves regularly. Leaves with tip and/or edge necrosis, e.g. B. fluoride damage should be reduced to the healthy part.

If the plant has grown well, it will likely need to be repotted. The decision to repot should be based on the appearance of the plant - whether it's top-heavy, whether it's filling the container with new shoots, or whether it has heavy root growth from the pot's drainage holes. Ideally, plants should be repotted in 1-inch increments. Planting in a container that is too large will give the roots more soil than they originally need. The excess soil holds extra moisture and creates overly wet conditions. Increase the pot size in smaller increments instead of doubling the pot size in one go (Figure 9).

pest control

Very few plants stay pest free forever. Pests are more common on indoor plants than diseases, since the indoor environment rarely provides favorable conditions for the development of leaf diseases. However, when plants are grown under stressful conditions (e.g. low light and too much water), soil-borne pathogens often develop.

The scales are ⅛ inch to ⅓ inch long and vary in color depending on the species. The three main families of scales are armored (the body covering can be separated from the body), soft (the body covering cannot be separated from the body), and mealybugs. Scales suck plant juices from leaves and stems, causing growth retardation, leaf discoloration, and tissue death. As a result of their feeding, sticky "honeydew" (digested plant sap) is excreted (except for armored scales). Honeydew provides a growth medium for a fungus called sooty mold which, if present, can spoil the plant's appearance and block light from reaching the leaf surface. Scales are usually unremarkable; By the time infestation is noticed, the population is usually very large (Figure 10 and Figure 11).

Mealybugs are soft-bodied, 1/5 inch to 1/3 inch long, and covered in white, waxy filaments, giving them a white, cotton-like appearance. Insects are often found on the new growth at the stem tip, where they suck plant saps, causing wilting and leaf clipping (Figure 12). Some types of mealybugs first appear on the underside of the leaves. Mealybugs excrete sticky honeydew that attracts sooty mold.

Aphids are soft-bodied, pear-shaped, 1/25 inch to 1/8 inch long, and usually green in color (but can be pink, blue, brown, yellow, or black). Aphids live on new growth or on the underside of young leaves, where they suck plant saps, causing deformed, ruffled growth of new leaves, buds, and flowers. Aphids also excrete honeydew. Aphids are usually wingless but develop winged forms when colonies grow too large (Figure 13).

Spider mites are the second most common pest problem in houseplants (Figure 14). The adult females are about 1/50th of an inch long and barely visible to the naked eye. Mites feed on the underside of young leaves. Affected areas are mottled grayish or yellow.

Networks form as a means of propagation. Spider mites thrive in hot and dry conditions.

While thrips are uncommon among houseplants, they primarily feed on patio and other outdoor plants (Figure 15). Thrips are small, slender, 1/25 inch to 1/12 inch long, and tan, black, or tan with lighter markings. Adults and larvae feed on shoot tips, flowers and leaves by sucking sap and cell contents. Injured tissue has a whitish or silver-speckled appearance due to light reflecting off the empty cell walls of dead cells.

What to do with plant problems?

pests

• The best method is prevention - buy pest-free plants.
• Remove a light infestation of mealybugs or aphids with a cotton swab dipped in rubbing alcohol.
• If outdoor conditions permit, move the affected houseplant outside to a sheltered area where natural predators will eventually come and rid the plant of the pest.
• Treat with insecticidal soap. Best results are achieved with plants that have been hardened in the indoor environment. New plants, unless acclimated (used to lower levels of light, fertilizer and water), will become tender and should be treated after the first few weeks. Add 2 teaspoons of insecticidal soap per gallon of water and wipe down leaves and stems with the soapy water and a soft cloth.
• A severe infestation may be too extensive to treat. Throw these plants away and don't put them on your compost pile.
• Do not bring beneficial insects into the house! They can do well in the greenhouse with large numbers of plants and pests, but there just isn't enough food in your home to sustain their population. Most pests can be controlled culturally on houseplants without the use of chemicals.

Another potential problem in indoor gardening is the appearance of various diseases. For disease to occur, three factors must be present: (1) a susceptible plant, (2) a viable pathogen, and (3) a favorable environment. Because the home has a very low relative humidity and water is often applied directly to the growing medium (keeping the foliage dry), the chances of leaf disease developing is minimal.

Leaf spot is the most common problem, but it's not usually caused by a disease. Leaf scalding, for example, occurs when water droplets on the leaves act as lenses, focusing excessive light on a spot, bleaching the chlorophyll and killing the underlying tissue. Patches with patterns are signs of disease, including a brown center, dark borders, and/or light borders called "halos." Dark structures may be present on the underside; these contain a dispersal agent called spores.

The most important thing is to avoid stress on the plants. A healthy plant is much more likely to fight a disease than a stressed one. Use a simplified key to identify the causative agent of a disease (Figure 16).

Soil borne pathogens are often found on stressed plants. Soil-borne pathogens attack plants at or below the soil line; The development of the disease is usually well advanced before symptoms are observed on parts of the plant above ground. Soil diseases are common when the growing medium is kept overly wet and fertility is high. Low light and overwatering create favorable environments for indoor soilborne diseases.

The most common causes of indoor stress are too little light and too much water.

Summary of cultural maintenance

Table 3 lists more than 200 plants and their cultural requirements. To summarize cultural care guidelines, the following abbreviations and coding numbers are used. These guidelines apply to actively growing houseplants.

L = light

1. Sunny light areas: At least 4 hours of direct sun
2. Bright Areas: Above 200 ft-c but no direct sun
3. Medium light areas: 75 ft-c to 200 ft-c
4. Dimly lit areas: 25 ft-c to 75 ft-c

T = Temperature

1. Cool: 50°F night, 65°F daytime temperature
2. Average: 65°F night, 75°F daytime temperatures
3. Warm: 70°F nighttime, 85°F daytime temperature

H = relative humidity

1. High: 50% or higher
2. Average: 25% to 49%
3. Low: 5% to 24%

W = irrigation

1. Keep soil mix moist
2. The surface of the soil mix should dry before watering again
3. The soil mix can be moderately dry before watering again

S = Recommended soil mix

Specific ingredients can be found in the different growing mixes under "Soil/Growing Medium". The soil mixes are coded as follows:

1. Flowering houseplants
2. deciduous plants
3. Bromeliads
4. orchids
5. Succulents and cacti
6. Make some
7. African violets and other gesneriads

bibliography

Manaker, G. H. (1997).Indoor plant landscapes: installation, maintenance and management(3rd ed.). apprentice hall.

McConnell, DB (1978).The indoor gardener's companion : a definitive, colour-illustrated guide to choosing and caring for houseplants.Van Nostrand Reinhold Company.

Status and revision history
Released December 15, 2006
Released October 13, 2009
Published with full review on December 01, 2012
Published with full review on January 05, 2017
Published with full review on May 27, 2020
Published with full review on July 21, 2022