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When a houseplant stops blooming or drops its leaves, the home gardener may be tempted to discard the plant rather than seek out the problem. Bud failure or leaf drop may be due to low temperature, poor soil, drafts, lack of fertilizer, too much or too little water, or too much or too little light. All these problems may be correctable. Saving the plant is entirely possible.
When you go to a nursery or garden center to buy a houseplant, you want a specimen that is appropriate for the conditions you can provide. And, of course, you want a healthy plant that is pest-free.
Appropriate Plants: The most important factor in choosing an appropriate species of plant is the amount of light it will receive in your home. To learn how to evaluate indoor lighting, read the section called Providing Light, which appears later in this chapter. Note whether the proposed growing area receives bright, medium, or low light. Take a houseplant reference book with you when you shop, or make sure your nursery has references available on-site. Look up your intended purchase to see whether the site can provide the light the plant needs. Flowering plants and cacti need the most sunlight. Pothos, cast-iron plants, and some ivies grow slowly but well in indirect light. Prima donnas such as orchids have specific light requirements in order to bloom; make sure your site can meet their needs before selecting such plants.
Healthy Plants: How can you tell if a plant is healthy? The leaves of a healthy plant are green unless they arenaturally variegated or multicolored, as are some pothos, Chinese evergreens, zebra plants, and others. Unhealthy leaves may have tips or edges that look burnt, brown spots, or a yellowish cast. Unhealthy leaves may appear crumpled or tend to droop. Readily apparent leaf problems can be due to powdery mildew, aphids, whiteflies, spider mites, or other insects. Inspect leaf undersides and leaf-to-stem junctions for signs of disease or insects. Of the plants that appear healthy, select the most compact and fully leafed.
When buying a flowering plant for indoor use, look for a specimen with ample buds as well as flowers. Minimal buds on a plant usually mean it has passed the peak of blooming; it will be another year before it blooms copiously again. A plant with many buds will be colorful throughout the current season. If you find a sturdy, well-budded plant with some flowers, give it a gentle shake. If many flowers drop off, the plant has been subjected to severe stress. Select a healthier specimen.
After bringing your purchase home, set it off by itself for about a week. Even though you did not see any insect pests, the plant may harbor microscopic insect eggs. Check the plant carefully after the quarantine period. If you see even a few insects, treat the new plant with insecticide before placing it near any other plant.
Purchasing the Perfect Pot
Among the many choices available for indoor plant potting are unglazed clay, plastic, and glazed ceramic in designs to match every decor.
A clay pot is especially appropriate on a porch or in a rustic atmosphere. Since moisture evaporates quickly through clay pot sides, use clay pots as containers for plants such as succulents, which tolerate dryness. If you place other types of plants in clay pots, they will need more moisture than normal. Since water tends to seep through clay pot bottoms, place a nonporous saucer underneath to prevent rug or counter stains.
Plastic pots are lightweight and often used for hanging plants. Plastic pots hold water longer than clay pots, so be careful not to overwater. Many plastic pots are sold with removable saucers.
Glazed ceramic pots are as effective in water control as plastic pots. However, many ceramic pots do not have drainage holes, a deficiency that can cause overwatering. Place a plastic pot with drainage saucer inside the glazed pot.
In nature, plant roots can spread out to seek nutrients. In a pot, what's there is what the plant gets. If vitamins and minerals are lacking, the plant fails to thrive. Nutrients are as important to the plant as adequate light and sufficient moisture.
Most houseplants can thrive in all-purpose potting soil. Fussier plants, such as African violets, may grow better in a commercial potting soil formulated especially for the species. Other types of commercial soils are formulated for specific situations—for example, terrariums. Soilless growing mediums are also available.
You can make your own potting mix, using varying proportions of garden soil, sand, peat moss, vermiculite, and leaf mold. The gardener who uses homemade potting mix, however, runs the risk of bringing in insect pests and disease organisms. Commercial potting soil is inexpensive, convenient, and free of pests and disease.
Water causes more plant problems than any other single factor. These problems include overwatering, underwatering, and using inappropriate water techniques or tainted water.
Too Much Water: A water overdose without adequate drainage rots roots slowly but steadily, causing plant death. One sign of overwatering is green moss that grows on the surface of the soil. Plant symptoms include lower leaf wilting, faded leaf colors, and poor growth. The lower portion of the plant's main stem, right above the soil line, may darken. Roots are brown and mushy.
If damage has not totally destroyed the roots, rescue attempts can include removing standing water, trimming brown roots, and repotting the plant in well-draining soil. An alternative is to take cuttings from healthy stems and start over.
Too Little Water: Many gardeners worry so much about overwatering that they underwater. A water-stressed plant conserves moisture by slowing or stopping new growth. Without adequate water, green leaves turn dull green or yellow. Drooping occurs. If buds are present, they may fall off.
When to water? Poke your finger about 1/2 inch into the potting soil. It should feel moist but not wet. If it feels dry or barely moist, water immediately and thoroughly. Ensure adequate drainage, or standing water will turn the underwatering problem into a case of overwatering.
Watering Techniques and Tainted Water: Water most houseplants from the top. Within an hour, pour off excess water from the saucer underneath the pot.
Most drinkable tap water is adequate for plants. Use it at room temperature. The sodium in some types of artificially softened water can prove a problem, however, if used consistently over a long period. Some tap water may also contain salts, which accumulate quickly in plant containers. Salt damage is evidenced by brown leaftips or edges. Damage occurs on older leaves first, and affected leaves eventually die. The plant may also be stunted, with brittle leaves that curl downward. An accumulation or overdose of fertilizer salts causes similar damage. If you see symptoms of salt accumulation, flush the plant thoroughly with water (for instructions, see page 22). If salts are built up on the rim or at the soil line in the pot, repot the plant in fresh soil to dilute salt levels.
Some gardeners collect rainwater for indoor plant use. Rainwater may carry pollutants, depending on where you live. In a pot, pollutants may accumulate quickly and deter plant growth.
The secret to providing appropriate light is to match the plant to the site.
Site Evaluation: How do you evaluate light? During prime light time, place a sheet of white paper on the table or sill where a plant will reside. Hold your hand about 12 inches above the paper. If a clearly defined dark shadow results, the site receives bright light. If a muted but clearly definable shadow results, the light is medium. If your hand shadow is barely visible, the amount of light is low. Make sure any plants you purchase can prosper in the lighting conditions you can provide.
Symptoms of Inappropriate Light: Inadequate lighting produces a leggy, weak plant that may suddenly drop its leaves. Growth slows. The lower leaves turn a lighter green, and the plant does not flower. Plants lean toward the light source; rotating the plants regularly prevents uneven growth.
An African violet that does not bloom is probably not receiving adequate light. These plants require about 12 hours of bright light every day.
Although most complaints are about insufficient light, some rooms are too sunny. Dry patches on leaves may be symptoms of sunburn. If the site gets hot enough, buds and flowers drop off and the entire plant may wilt. To prevent further damage, try moving the plant away from the window; shading the window with filmy curtains; or replacing the plant with a heat-tolerant species, such as a cactus.
Cacti are the plants of choice for sunny locations. Watering them once a week will do, except when you want them to flower. Do not allow cacti to dry out totally during the flowering season.
Artificial Light: In sites that receive little sun, artificial light may be the only answer. Fluorescent bulbs and incandescent bulbs provide different types of light. Cool-white fluorescent bulbs give off little heat. They do not bake the moisture out of plants, even if placed within 4 inches of the foliage. With adequate fluorescent lighting, you need no outdoor light; you could grow plants in a closet if you provided a fan for air circulation.
To help support plant growth with incandescent light, you must use a bulb of at least 100 watts. Such a bulb produces a lot of heat; keep incandescent light at least 2 feet above plant tops to keep from burning the foliage and baking the soil.
Outdoors, soil is constantly improved with leaf mold, earthworm castings, decaying plants, and animal droppings.
Indoors, once a plant has used up the nutrients in the pot, there's nowhere for it to get more unless the gardener adds some type of fertilizer.
Symptoms of Nutrient Shortage: Plants quickly reflect a nutrient shortage. A nitrogen shortage shows up as yellowing leaves and poor growth. If a plant has leaves a darker green than normal, poor growth, and leaf stems with a purplish tinge, a shortage of phosphorus is probably the cause. A potassium shortage appears as yellowing leaves with brown tips and edges. A lack of iron appears as the yellowing of older leaves, on the bottom portions of stems. This yellowing starts at leaf edges and progresses inward.
Fertilizer Selection and Application: Many types of indoor plant fertilizer are available. The numbers on the container describe the relative proportions of nitrogen (N), phosphorus (P), and potassium (K). The designation "20-20-20" means the fertilizer contains equal portions of each element. A 5-10-5 mixture is higher in phosphorus than in nitrogen or potassium.
Nitrogen helps make healthy green leaves. Phosphorus encourages a strong root system as well as luxuriant flowers. Potassium aids in disease resistance, promotes plant vigor, increases bloom, and strengthens stems. In addition, plants need trace elements, such as iron, which is essential in minute amounts for chlorophyll production and enzyme functioning. Plants grown in synthetic mediums, such as sand or vermiculite, need a dose of one-third strength fertilizer with each watering, because they contain no soil nutrients.
A little bit of fertilizer may be fine, but a lot of fertilizer is almost always too much. Extra fertilizer accumulates in soil, causing tip burn or browning. Too much nitrogen causes rapid growth at the expense of plant vigor. The plant becomes large and spindly, does not set flowers, and is prone to insect invasion.
If you have applied too much fertilizer, take action quickly. Repot the plant in fresh soil or rinse and drain the current soil to wash out fertilizer residue. When applying fertilizer, always follow label instructions.
Outdoor potted plants purchased for indoor bloom—such as chrysanthemums, freesias, hydrangeas, hyacinths, and narcissus—may be subject to rapid bud withering if kept in areas with continual hot, dry air. Avoid placing these plants in extremely sunny kitchen windows or near microwaves, ovens, and heating vents.
Given appropriate light, sufficient water, and ample air circulation, outdoor plants will bloom indoors for several weeks. If the soil is allowed to become dry during blooming time, future flowers may not form, even though foliage may recuperate.
When bulbs and other basically outdoor plants cease flowering, they probably will not do so again indoors. Plant them outdoors in appropriate surroundings, however, and they will bloom normally.
Holiday plants, such as poinsettias and Christmas cacti, are reared under controlled conditions to produce blooming during specific seasons. Gardeners often expect them to bloom again next year at the same time. This will probably not happen unless light is strictly regulated.
Extended periods of light encourage foliage rather than flowers. For poinsettias and Christmas cacti to reflower, you must provide total uninterrupted darkness during evening and night hours. After poinsettias bloom the first time, cut back stems to 8 inches and repot the plants in fresh houseplant soil. Beginning in October, cover both poinsettias and Christmas cacti with a large carton from sundown to sunup. Remove the carton every morning. Do this until flowers appear.
Gift plants, such as azaleas, may lose their flowers quickly indoors if placed in hot direct sun. Do not let them dry out. Place them away from drafts, and keep them moist and cool. Getting azaleas to bloom indoors a second time is extremely difficult. Even with the best care, it may take several years. After the plants bloom the first time, some gardeners place them outdoors in appropriate surroundings, where the azaleas may do well. Others keep azaleas as foliage plants indoors.
Other gift plants that generally do not bloom again indoors are cineraria and cyclamen. Try placing them outdoors in good soil and growing conditions, and after the first or second spring they may surprise you with flowers.
Problems Common to many
Too little water
Problem: Leaves are small, and plants fail to grow well and may be stunted. Plant parts or whole plants wilt; leaves may yellow and drop off. Margins of leaves or the tips of leaves of narrow-leafed plants may dry and become brittle but still retain a dull green color. Bleached areas may occur between the veins. Such tissues may die and remain bleached or may turn tan or brown. Plants may die.
Analysis: Plants need water in order to grow. Besides making up most of the plant tissue, water is also the medium that carries nutrients into the plant, so a plant that is frequently short of water is also short of nutrients. Water also cools the leaves as it evaporates from them. If a leaf has no water to evaporate, it may overheat in the sun and burn. If plants wilt and then are given water, sometimes the margins or tips of the leaves will have completely wilted and will not recover. If this occurs, the margins or tips will die and become dry and brittle but will retain a dull green color.
Solution: Water plants immediately and thoroughly. If the soil is completely dry, soak the entire pot in water for a couple of hours. The rim of the container should be submerged. Or add a soil penetrant (available in garden centers) to the irrigation water. Water again when the soil just below the surface is barely moist, applying enough water so that some water drains from the bottom. In large containers (more than 10 inches wide and 10 inches high), water when the soil 1 to 2 inches below the surface is barely moist.
Too much water or
Problem: Plants fail to grow and may wilt. Leaves lose their glossiness and may become light green or yellow. When the plant is lifted from its container and its rootball is examined, the roots are brown and soft and do not have white tips. The soil in the bottom of the pot may be very wet and have a foul odor. Plants may die.
Analysis: If the soil is kept too wet, the air spaces are filled with water, and the roots are weakened and may die. Although plants need water to live, the roots also need air. Weakened plants are more susceptible to root-rot fungi, which wet soils favor. Plants with diseased roots do not absorb as much water as they did when they were healthy, so the soil remains wet. If roots are damaged or diseased, they cannot pick up water and nutrients needed for plant growth.
Solution: Discard severely wilted plants and those without white root tips. Repot into a smaller pot until roots regrow. Clean the pot before reuse. Do not water less severely affected plants until the soil is barely moist. Prevent the problem by using a light soil with good drainage.
Problem: The leaf margins of plants with broad leaves or the leaf tips of plants with long, narrow leaves turn dark brown and die. This browning occurs on the older leaves first, but when the condition is severe, new leaves may also be affected. Plants may be stunted, with brittle leaves curling downward. On some plants, the older leaves may yellow and die.
Analysis: Salt damage is a common problem on container-grown plants. The roots pick up soluble salts, which accumulate in the margins and tips of the leaves. When concentrations become high enough, the tissues are killed. Salts can accumulate from water or from the use of fertilizers, or they may be present in the soil used in potting. Salts accumulate faster and do more harm if plants are not watered thoroughly. Water that is high in lime does not cause as much salt damage as water that is high in other salts.
Solution: Leach excess salts from the soil by flushing with water. Water thoroughly at least three times, letting the water drain from the pot each time. This is most easily done if the pot is placed in the bathtub, in a basin, or outside in the shade to drain. If a saucer is used to catch the water, empty the saucer 30 minutes after each watering. If the plant is too large to lift, empty the saucer with a turkey baster. Never let a plant stand in drainage water.