Indoor Plant Care
Indoor plant care: Different aspects of raising healthy and beautiful house plants, as well as keeping them alive.
Most people acquire houseplants as gifts: either as whole plants or in the form of slips for rooting. Commercial producers start houseplants from seed - and you can do the same. Starting them from seed is an easy, economical and satisfying way to acquire a variety of interesting houseplants.
You can start houseplants from seed indoors the same way you start vegetables and annual flowers for transplanting to your garden. Plants that can be easily started from seed include flowering maple, asparagus ferns (not true ferns), palms, crotons, false aralias, and freesia, though there are many, many more.
From Seeds to Seedlings
Seeds can be started in pots or seed pans. For the growing medium, prepare a mixture of sand and peat moss in equal portions by volume. Use fine sand and peat moss for small seeds. Larger seeds can often be started in slightly coarser mixtures that can include vermiculite or perilite. It is also possible to start seeds in commercial sterilized potting soil; if this is used, pack the soil down firmly, sprinkle the seeds evenly over the surface of the soil, then sieve a small quality of the soil mixture over the seeds. This will assure that the seeds are in close contact with the soil.
As a general guideline, plant at a depth that is twice the diameter of the seed. Very small seeds such as begonia seeds are left uncovered.
After planting, moisten the medium without disturbing the seeds. Keep the seeds moist until they germinate. To keep the moisture level high, cover the pots or pans with a sheet of glass or place them in clear plastic bags and tie. For seeds that take a relatively long time to germinate, you may have to add water occasionally to keep the medium damp.
Many houseplants will take more than 3 weeks to germinate - so be patient. The seeds can be kept in the dark or given indirect light, but it is important that they receive a bright, indirect light upon germination. When the seeds germinate, be sure to remove the plastic or glass; otherwise the seedlings will be susceptible to dampening-off and other problems.
Seed packages will usually have directions about recommended care of the seedlings. When the seedling are about 5 cm (2 in.) high, transplant them to larger containers. How large should these containers be? For fast-growing plants such as impatiens and coleus, you can transplant the seedlings into a 10 cm (4 in.) container. Slower growing plants are best transplanted first into small (2 in) containers and then repotted into successively larger containers as the plants grow.
Ferns are started from spores, which are very small - the size of dust particles. Starting ferns from spores is not difficult. All you do is buy the spores, and plant them just as you would fine seeds, sprinkling the spores over the surface of the medium. The medium should be damp as for seeds. In the case of spores, however, keep the plastic or glass cover on after the plants start to grow - because ferns benefit from humid conditions. As the fern approaches transplanting size (on average, 5-8 cm or 2-3 in.) gradually remove the plastic or glass to expose the plants to room conditions. Transplant as for seeds.
Humidity and Houseplants
Humidity is a measure of the amount of water that air will hold. The water is usually in the form of invisible droplets. At 100 percent humidity the air cannot hold any more water. The highest humidity often occurs on hot days, creating a "muggy" feeling. Fog occurs when the air is saturated and the invisible water now becomes visible.
Humidity is measured relative to temperature and is called relative humidity (RH). The measurement is taken this way because humidity and temperature are directly related: the warmer the air, the more water it can hold.
Humidity in the Home
If warm air holds more moisture than cold, then why is it so dry inside the house in winter? Remember that the furnace is taking dry outside air and warming it. If no water is added to this outside air, then it will still be dry. You can increase the humidity inside to a certain extent by adding water to the air. Warm, moist air is always being lost from the house, and cold dry air is always being brought in, so high humidity in the entire house is not possible.
When warm, moist air comes in contact with a cold, dry surface, the water in the air condenses. This is very common on windows, and is an indication that the humidity inside the house is higher than outside. If the inside walls of the house are cooler than the air inside the house, water can condense on the walls, and can cause wallpaper to come unstuck, but don't rely on this as a means of stripping wallpaper!
Humidity and Plants
Humidity is important to plants because it partly controls the moisture loss from the plant. The leaves of plants have tiny pores in them called stomata. Carbon dioxide enters the plants through these pores; oxygen and water leave through them.
The humidity inside a plant is close to 100%. A plant growing in a dry room will lose moisture because water always moves from high to low humidity. When the difference in humidity is large, the loss of moisture from the plant is rapid and severe.
Most houseplants prefer a humidity of about 60%. Cacti, succulents and plants native to desert environments tolerate much lower humidity (30-35%), but prefer not to drop below 20%. House plants that are native to tropical rain forests require much higher humidity, 90% for example, and thus pose problems for most home owners. Plants that require a very high humidity are best grown in terrariums or closed containers where it is possible to regulate the humidity.
Damage from excess humidity - Under very humid environments, fungal diseases can spread. This seldom happens during winter, but can be a problem in fall when the temperature is cool and the humidity is high. Mildew on plant leaves is an indication of excess humidity and lack of Damage from dryness - Plants that prefer a more humid environment, but that are forced to grow in a dry environment will commonly suffer damage to younger leaves and to leaf tips. New leaves and leaf tips are the area of the plant with the most actively growing cells, and these cells are the most susceptible to dry air. Older leaves that are fully formed may be shed as a result of lack of humidity, but they will not be deformed or damaged by the dry air. Plants stressed in this way very frequently shed flower buds, or flowers die soon after opening.
There are a number of ways that a home owner can increase the humidity in the room or around the plants.
Humidifiers - Using a humidifier is by far the most effective way to increase humidity. Humidifiers that attach directly to the furnace will increase the humidity throughout the house. Portable humidifiers can be used to increase the humidity in one or more rooms.
Changing locations - Bathrooms and kitchens, if they are sunny, often have a higher humidity than other areas of the home, and may be more suitable for house plants requiring extra humidity.
Double potting - Take a small potted plant or a number of small plants, and put them in a larger pot. Fill the area underneath and around the small pots with peat moss. Keep the peat moss constantly moist. As water evaporates from the peat moss, it increases the humidity around the plants. Make sure the large pot has a tray underneath to catch excess moisture from the peat moss. A similar approach is to place a house plant in a basket lined with moist peat moss.
Pebble trays - Fill a large plant saucer with pebbles or stones. Place a number of small pots (or a large pot) on top of the stones. To assure that the pots do not contact the water, you may wish to place them on saucers which sit on the pebbles. Now fill the large plant saucer with water up to the level of the pebbles. Make sure the saucer with pebbles is large enough to be effective - the larger the surface area of pebbles, the more effective the method will be.
Totems for climbing plants - Take chicken wire and roll it into a totem (tube). Fill the tub with peat moss. Anchor the tube in the plant pot and then wind the climbing plant around the tube. Keep the peat moss inside the tub moist. Do not worry if the plant forms roots into the totem, but if this occurs make sure the totem is kept evenly moist.
Grouping - Moisture loss from one plant can benefit the plant next to it. Try and group plants with similar watering requirements together, and keep them close to each other. The closer together they are, the more effective the method.
Misting - This is the least effective but often the most used method. Misting plants with tepid water will result in a layer of water on the leaves, which will reduce the transpiration of water from the leaves. However, soon after misting, the water will evaporate, and once this occurs, the air is once again low in humidity. If plants are misted too often or too much, however, fungal growth and tissue rotting may result. Plants with hairy leaves cannot be misted, for leaf spotting will likely occur as a result.
PLANTS PREFER PURE WATER
Water that is very high in salts such as sodium, calcium and magnesium can injure houseplants if used over a prolonged period. Our water in Saskatoon is not high enough in salt content to harm houseplants, but in many areas of the province, plants are at risk. Water high in salts can cause leaf necrosis (speckling of the leaf), leaf burn (drying of leaf tips and margins), and in severe case, leaf drop.
If water high in salts is used, in time the salts will accumulate and show up as a white or tan crust at the edges of plant pots. The same crust may form on the soil surface and around the plant stems. Misting houseplants with water high in salts will cause a white residue to form on the leaves, which can lead to permanent leaf spotting.
Solving Salt Problems
One approach to these problems is to reduce the salt buildup in various ways. Begin by removing the salt crust from the soil and pot. Next, flush the pot with rain water or melted snow, which are very low in all salts. Some of the salts in the soil will dissolve in the water and drain away. Flushing with tap water will leach some salts away, but because the tap water itself will be high in salts, it is not as effective as rain water or melted snow. Watering houseplants with a strong tea solution will help to offset the damaging effects of high levels of salts in the soil.
A more direct approach is to reduce the salt content of the water before using it. Some homeowners boil water to remove the salts. This procedure does remove some salts, which build up as a scale inside the kettle, but many salts remain in the water. There are a number of different systems for salt-removal available to the homeowner. Before I discuss them, here are a few more facts about water and salts.
Hard and Saline Water
Water with a high concentration of calcium and magnesium is referred to as "hard" water. How high is high? Hard water has greater than 150 parts per million (ppm) of calcium and magnesium. Saline water has a high concentration of many different salts, including calcium and magnesium. The salinity of water is measured by its electrical conductivity; the dissolved salts increase the conductivity of the water, so the higher the salinity, the higher the conductivity.
Soaps used for laundry and washing are not very effective in hard and saline water, and for this reason many households with high-salt water supplies "soften" their water before using it.
The ion exchange or salt water softener - This is the system most commonly used by homeowners to soften water for laundry and washing. But it may not be suitable if you want water that is safe for your houseplants. Somewhat paradoxically, this system uses common salt (sodium chloride) to soften the water. Small beads of resin capture the calcium and magnesium salts in the water; as part of this process, sodium is released into the water. The amount of sodium released is equal to the amount of calcium and magnesium in the untreated water. If the water is very hard and contains high amounts of calcium and magnesium, the treated water will contain an equally high amount of sodium. Though the treated water will be suitable for laundry and washing, it will be most unsuitable for plants because sodium in high concentrations is even more harmful to plants than calcium and magnesium!
Reverse Osmosis System - This system is commonly used to produce purified water for drinking. The treated water is very low in salts and safe for houseplants. In contrast to the ion exchange system, the reverse osmosis system has a relatively small capacity and is not practical for treating large volumes of water. It uses a "semi-permeable membrane" that allows water to flow through and captures most salts and minerals. The membrane must be cleaned and eventually replaced.
Deionizing and distilling systems are also very effective in removing salts from water. Like the reverse osmosis system, these systems have a small capacity. The costs of purchasing and operating them are quite high, though the treated water is very pure and safe for houseplants. Deionized water can be purchased at some stores.
Urban systems - Some urban centres choose to soften their water supply. Saskatoon adds calcium oxide to the water. When the water is aerated, calcium carbonate precipitates out and is removed. This process, which reduces the calcium content of our water, is used from October 1-May 1.
Saskatoon and many other urban centres also add chlorine and fluoride to water supplies for health reasons. Some plants may be damaged by fluoride and chlorine, even at the very low levels present in our water. Susceptible plants include Hawaiian ti, spider plant, wandering Jew, prayer plant, some palms and calathea. Let the water from the tap sit for a day at room temperature; this will allow the chlorine and fluoride to evaporate.
Growing house plants is a challenging and rewarding hobby that can be enjoyed by everyone and need not be difficult. Give plants what they need and they'll do well for you. Give them just about what they need and they hold their own. Deny too many of their needs and plants fail.
Take time to learn the cultural needs of a particular plant when you purchase it and keep a watchful eye out for possible disease and insect problems. If a plant has poor color, or distorted leaves or flowers, or if the plant tends to droop, something is wrong. These distress signals tell you the plant is having problems and corrective steps should be taken.
Check plants over carefully before purchasing. Pick one which has a healthy green color and shows signs of new growth. Make sure that the pot has good drainage and the plant is not root bound. Avoid plants with abnormal white or brown lumps on the leaves or stems. Webbing or a speckled leaf appearance could indicate an insect or related pest problem. A new plant should be isolated from other plants in the home for two to three weeks to avoid exposing other plants to problems which may develop. If a problem does develop, you have not exposed your other house plants.
Plant roots must have air, food and water. Potting soil must be porous enough to allow drainage of excess water and to admit oxygen (soil aeration) needed by the roots.
Garden soil may appear ideal for potting indoor plants but actually causes problems. This soil may be wonderful for outdoor gardening under natural conditions, but after a few months the garden soil becomes hard and almost rock-like in a plant pot. Plants in garden soil grow satisfactorily for a month or two, but soon the lower leaves turn yellow and the plants become unthrifty. This problem is the result of poor drainage and the lack of soil aeration due to improper soil structure. Most garden soils become compacted with time and house plants grow poorly in compacted soil.
A proper soil mixture is of utmost importance to a house plant because the roots are restricted by the pot. A good potting soil should have the capacity to retain some air and moisture and yet drain well and hold nutrients. Sand or perlite added to the soil will improve aeration and drainage. Clay or organic matter will help retain water. Organic matter, plus commercial fertilizers, will maintain adequate nutrient levels. Modern "soil-less" potting medias do not contain soil so the addition of fertilizer is required to provide all essential plant nutrients.
For general use, a good soil mix includes approximately equal parts of good garden loam, organic matter (preferably peat moss, although well-rotted manure or leaf mold will do) and sharp sand or perlite. When sandy soil is used in the mixture, reduce the amount of sand or perlite.
Always use pasteurized soil when repotting at home.
Always use thoroughly cleaned potting containers with proper drainage holes. Before reusing any pots, they should be scrubbed clean and thoroughly rinsed in a solution of one part household bleach to nine parts water to kill disease organisms present. Cover the drainage holds in the pot with pieces of broken clay pots or coarse gravel. Next add enough potting soil to bring the soil level of the finished planting to about one-half inch below the rim of the pot. This top space serves as a reservoir for watering.
When repotting, cover the old soil level with about one-half inch of new soil. Firm the new soil around the root ball and water well to eliminate air pockets. Keep transplants away from drafts and provide extra humidity to reduce transplanting shock. You can provide extra humidity by covering plants with plastic for a day or two. Water when the soil feels dry but avoid fertilizing the plants for a few weeks until new shoot growth is evident. Excess fertilizer can damage the newly developing root hairs and delay plant growth.
Close observation and good judgment are essential for proper house plant watering. Growing conditions vary from home to home and room to room due to variations in light, temperature (day and night) and humidity. Plants with roots in shallow containers may need daily watering, while plants in large tubs may go several weeks between waterings. Succulents and other dry-soil plants require less watering than moist-soil plants such as ferns and African violets.
Proper watering keeps the soil moist enough to supply the plants' needs without drowning the roots. Saturated soil drives out air, and roots can die from lack of oxygen. Proper pot drainage is critical. All the soil in a pot should be thoroughly wetted each time the plant is watered. Always empty the drainage water from the catch basin beneath your plant container after each watering. This will reduce the possibility of waterlogged soil and prevent the dissolved salts in the water from being drawn back into the soil. Soil should dry to the point that the plant approaches moisture stress between watering intervals.
Do not use water that is unusually high in salts or that has been run through a water softener to water plants. Rain or melted snow are good alternate sources of water for house plants. Some plants are sensitive to the chlorine gas in city water systems. Letting a container of tap water sit overnight before use will allow most of the gas to escape.
Many brands of fertilizers are designed for house plants. Follow the manufacturer's directions and do not assume that twice the recommended amount is better than the recommended amount; overfeeding may damage your plants.
Plant injury can be reduced by leaching or rinsing out part of the dissolved fertilizer with clear water if over fertilization occurs. Use a container with holes in the bottom to allow thorough drainage. Place the pot in a sink and water liberally three to four times at half-hour intervals, allowing the water to flush out the dissolved fertilizer and other accumulated salts.
A white, flaky material on the soil surface of potted plants is often observed one to several months after potting. These are mineral salts that accumulate in the soil. Well water in North Dakota contains varying amounts of dissolved salts, as does the fertilizer you apply. With continuous watering, these dissolved salts accumulate in the soil and appear on the soil surface. The salts can be flushed out of the soil from time to time to prevent salt injury to your plants. Leaching (rinsing) the soil of most house plants every three to six months is a good cultural practice and will reduce the accumulation of salts in the soil. Clay pots which have accumulated salts should be soaked in hot water for 24 hours before reuse.
Fertilizer will not cure all ills. Fertilizer will not help a plant that is suffering from poor drainage, insect infestation, disease or over-watering.
House Plant Trouble Signs
Wilting or partial wilting will often be the result of improper water relations in the plant. If sudden wilting is diagnosed, check the roots, pot or soil for the trouble. Some common causes are a lack of water, excess water, root rot, too much fertilizer and/or a salt buildup. Check the cause by pressing your finger, up to the first knuckle, into the soil. If the soil is dry to this depth, the plant needs water. If the soil is wet, too much water in the root area may be the problem. The roots may be saturated or rotting and incapable of absorbing water from the soil and supplying it to the leaves. Over watered plants should be repotted into fresh soil. (Refer to the section on yellowing and death of all leaves and poor growth for more information on root rot.)
Plants which are pot bound may wilt because the roots are strangling each other. Don't be afraid to remove the plant from the pot and examine the roots to see if they are too dry, too wet or diseased. To remove, merely invert the plant and lightly tap the edge of the container on a solid object while holding the plant and soil ball. You may find the soil mass is completely enveloped in roots and the plant needs repotting.
Sudden loss of leaves is frequently caused by a rapid temperature change. It may also be caused by such factors as prolonged hot or cold drafts, dry air, exposure to gas or furnace fumes or by changing the location of the plant from a sunny to a dark location. Ficus benjamina, commonly called weeping fig, frequently has sudden leaf drop when moved to a location with lower light intensity.
Yellowing or death of leaves may indicate a nutrient deficiency, usually nitrogen or iron. First apply a nitrogen fertilizer. If the foliage does not appear greener after three to four days, do not add additional nitrogen. Instead apply a chelated iron product. Iron is essential to healthy green leaves and may be present in the soil but in a form which the plant cannot use. Chelated iron is in a form which is readily available to the plant roots.
The yellowing and death of lower leaves may occur if plants become pot bound because of extensive root development. Rubber plant, Dracena, Diffenbachia and other woody plants are especially prone to this problem. When the lower leaves first start to yellow, apply extra nitrogen fertilizer or consider repotting. Occasional lower leaf drop may be normal. The length of time a plant will hold its leaves varies from species to species.
Yellowing of all leaves and poor growth may be due to excessive soil moisture and/or to root rot. If the drainage hole in the pot or plant box is plugged or if the plants constantly stand in water, the soil will be waterlogged and lack sufficient oxygen.
If a root rot problem is suspected, remove the rootball and check the roots. Healthy roots and root tips will be white or cream-colored. Rotted roots are a brown-black color and may appear slimy. Severely rotted roots may be hollow and easily broken between the thumb and index fingers.
Destruction of the roots by soilborne fungi and nematodes may cause a yellowing of the entire plant. Severe infestations of mites, aphids and scale insects, fertilizer burn, improper light and temperature, or improper pH all may cause plant yellowing. Soil pH prefers to the acidity or alkalinity of a soil measured on a scale of one to 14 with seven being neutral. Anything below seven is acid and anything above seven is alkaline.
Some plants such as the Norfolk island pine and Boston fern require an acid soil medium. This can be achieved by using a potting mixture high in peat and by using an acid fertilizer. Acid fertilizers help to reduce the pH of the soil. Most North Dakota well and river water is alkaline, so regular use of an acidifying fertilizer would be advantageous to plant growth .
Finely specked leaves with a faint mottled, lighter color may be infested with spider mites. When the mites are plentiful, the upper and sometimes the lower surface of the leaves may appear dusty due to their webbing. To check plants for spider mites, shake several suspect leaves or branches over a sheet of white paper. Look closely at the specks which have fallen on the paper. If they are moving, they are spider mites. More information on mites and their control is give in the chart that follows.
Bronzed or abnormally reddened leaves indicate cold temperature damage or a deficiency of phosphorus or potassium. Check the recommended temperature range for the plant. If a nutrient deficiency is suspected, fertilize with a complete fertilizer or repot in new soil.
Unnaturally small pale leaves and spindly plants are most generally the result of insufficient light. This is especially common during the winter or when outdoor or greenhouse grown plants are brought into the home. Small leaves might also indicate a need for fertilizer.
Brown leaf tips and margins can be caused by exposure to hot dry air, improper watering, insect feeding, salt accumulations or objects rubbing against the leaves. Water which is chlorinated or contains added or natural amounts of fluoride can harm sensitive plants. Perlite (the white material in many potting mixes) and fertilizer products containing fluoride may release enough fluoride to harm sensitive plants. Spider plants, especially the variegated variety, are very sensitive to fluoride and are often seen with leaf-tip burn. Occasionally flushing the soil should help to reduce a fluoride salt buildup.
Bleached or faced spots on leaves are sometimes caused by direct sunlight burning plants that require shade or are not yet accustomed to large doses of direct sunlight. Chemicals and plant cleaning products can also injure leaves.
Other leaf spots, varying in description, may be caused by aerosol products, hot grease in the kitchen area, cold water (especially on African violets and gloxinias) or the sun shining on wet leaves. In rare cases a pathogen may be involved. For more information on plant pathogens see the table that follows.
Plant distortion (leaf thickening, curling, leaf and flower drop) accompanied by leaf yellowing and browning may be due to gas fumes or pesticides which are toxic to the plant. Plants are very sensitive to gases and will show symptoms before the gas concentration is at a level detectable to humans. Garden soil that is contaminated with agricultural chemicals and used for potting house plants can result in chemical injury to the house plants.
White substances on the soil surface may indicate two things. If crusty or crystalline, it's probably an accumulation of salts. The crusty surface layer of soil can be removed and replaced with fresh soil between repottings. Refer to the previous section on "Feeding" for more information.
A white or light yellow mold-like growth may indicate the presence of a saprophytic soil fungus, a fungus that lives on dead or decaying matter. The fungus will not harm the plant but may indicate unsterile potting medium or an over watered plant.
Light brown corky scabs, usually occurring on the underside of leaves and along stems, are the result of excess water. This condition is known as oedema. Careful watering and good drainage will minimize this problem.