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Q. The new leaves on my orchids turn black and mushy when they are about 6 inches long. I have had cymbidiums a long time and never had this problem. What is wrong?
- G. M., Daly City, CA
A. "There are two fungal diseases that can cause the symptoms you describe; black rot and bacterial soft rot. Black rot (caused by a fungus, Phytophthora) attacks the leaves, pseudobulbs, and roots of orchids, causing them to turn black. You can cut out the damaged portion of the pseudobulb and remove the affected leaves to stop the spread of the disease. Be sure to isolate the sick plants so the disease doesn't spread to the healthy ones.
Bacterial soft rot symptoms begin with amber-colored spots on the bases of the affected leaves. These turn brown and spread very rapidly, eventually becoming a chestnut brown and then black as the disease progresses. Sometimes it's best to discard diseased plants rather than risk the spread to other plants.
Orchids thrive in average household temperatures, bright light (10 to 15 hours each day), and moist soil. They require moist air, so put the pots on a tray filled with pebbles in which you keep a half-inch of water. Mist the leaves occasionally, too. Orchids don't like cold drafts or direct sunlight. If you're meeting all of these cultural requirements and the plants continue to show signs of disease, you may want to toss out the affected plants and start all over with new plants, sterilized pots and fresh potting soil."
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Q. I have 2 beautiful orchid plants. The leaves are turning yellow and falling off. What should I do?
- U. N., San Francisco, CA
A. "These symptoms may indicate hot, stuffy conditions or insufficient light. Orchids like daytime temperatures around 70F during the summer and 60F during the winter, with a 10 degree drop at night. Cool nights are important to the health and flowering ability of your plant. Orchids require 10-15 hours of light each day, so you may need to supplement natural light with artificial light during the winter months when the days are short. Orchids like moisture and humidity, and appreciate being misted once or twice each day. To increase humidity around the plant, place the pot on a layer of rocks in a tray of water. As the water evaporates it will provide moist, humid conditions around your plant. Try adjusting the growing environment and your orchid should recover."
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Q. Two weeks ago I bought a large poinsettia, and already it is wilting. The soil is moist, so I know it's not wilted from being too dry. Why is this happening, and what can I do to help it recover?
- I. Y., San Francisco, CA
A. Poinsettias thrive in sunny indoor sites, in average household temperatures. They are sensitive to drafts or sudden temperature changes, and prefer moist (but not soggy wet) soils. If any of these conditions are not met, the plant will react by wilting, dropping leaves, and dying. Make sure you are not overwatering. (Wilting can be a sign of overwatering as well as underwatering.) For large containers, wait until the soil is dry down an inch or so before watering. Try placing it in a sunny window; it may regain its health.
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Q. Can you help my ailing ivy topiary? It has what looks like white mold on the potting soil and some of the leaves are turning brown and/or yellow.
- P. L., Kannapolis, NC
A. "If you've had the plant for a while, the white "mold" on the soil surface may be a buildup of minerals from the water and/or fertilizers. Scrape what you can off the soil surface, then flush the soil by saturating it and letting it drain; do this several times. Be sure to let it drain well at the end. Repeat the process every few months. If the plant is relatively new, or newly repotted, the white substance may indeed be mold, which indicates overly moist conditions. Allow the soil to dry out somewhat between waterings, and place the plant where it will receive good air circulation.
Yellowing foliage can be caused by a variety of things: over- or underwatering; exposure to a warm draft such as from a heating vent; lack of humidity; physical damage to the supporting stem by bruising, pruning or a training tie becoming too tight; a need for repotting into a larger pot; or by pests.
Look carefully for webbing on the undersides of the leaves which would indicate a spider mite problem. If you find these, wash the plant in a spray of lukewarm water twice a week and spray with insecticidal soap according to the label instructions. Remove any browning leaves and webbing as soon as you see them. Increase humidity around the plant if possible; a pebble tray filled with water works well for this."
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Q. My African Violet plant has light brown spots on its leaves. This happened to its "sister," and that one eventually died. This plant still looks healthy and blooms regularly. I can't find any bugs. What is wrong?
- N. L., Mission Viejo, CA
A. "There is a fungal disease called botrytis that causes brown spots on the leaves of African violets. High humidity, inadequate light levels, and poor air circulation contribute to the development of the disease. The best way to control it is to improve growing conditions and avoid overhead watering. Space plants so that the leaves of adjacent plants are not touching to minimize spread of the disease. Also, keep a close eye out for mites, because mite injuries are a common site for the fungus to enter the plant. Note that African violets are also very susceptible to root and crown rots, especially if they are overwatered.
There are several pests that regularly attack African violets in addition to mites, including thrips and mealybugs. Examine the plant frequently, checking the undersides of leaves for bumps or spots or webbing. Look also on the stems and in the crown of the plant."
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Q. My mom has a hibiscus she brought indoors for the winter, but over the last month it has been losing leaves. It gets good southern exposure and receives plenty of water. Any ideas?
- S. B., Woodridge, IL
A. "The most common reason for a hibiscus to drop leaves is the soil being too dry, but you say that can't be the problem so we have to look elsewhere. You also don't mention any irregularities such as pests or residue/mold on leaves so we will rule those out as well. That leaves us with two other probabilities: too much water, or a drafty area.
Hibiscus are very picky about watering -- it must be just right. They also won't tolerate drafts, hot or cold. They should be kept out of doorways and away from drafty windows and air vents. Overfertilizing or buildup of fertilizer salts is another possibility. Houseplants should only be fertilized during the spring/summer months (March through August as a rule of thumb). Occasionally flood the soil with water and allow to drain thoroughly, to rinse away any built-up salts.
When bringing plants indoors after a summer outside, make the move gradually so the plant can become accustomed to the lower light levels indoors. Start by placing the plant in a sheltered spot outdoors, out of direct sun, for a few weeks. Then move it indoors to the sunniest place you have. After a few more weeks, you can move it to its winter home -- for hibiscus, that should be a place with bright light."
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Q. I repotted my ficus and did a massive pruning job, and I'm afraid I may have harmed the plant. I have placed it outside in a sunny area and am crossing my fingers. The leaves have started to turn a yellowish white from the center outwards. Is there anything you can suggest to help turn this plant around?
- J. W., Salt Lake City, UT
A. Poor pruning can injure or kill a plant, but most plants have incredible recovery skills, taking abuse and thriving in spite of it all! It sounds as though your ficus is responding more to the direct sunshine on its leaves than to the massive pruning it has undergone -- it has sunburn! Plants that live indoors need to be placed in a protected area for a few weeks when they're first taken outdoors. Put your ficus in a shady spot that's shielded from strong winds, and gradually move it into more direct sun over the course of a few weeks. The affected leaves will fall off but new growth should come from the twigs and branches once it's had some time to recover.
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Q. I have a very large peace lily in my living room and I try to take extremely good care of it. However, no matter what I do, the margins of the leaves turn brown and crisp. What am I doing wrong?
- T. W., Spring City, TN
A. "Brown edges on houseplant leaves are usually caused by one of two things: overwatering or salt burn. Peace lilies (spathiphyllum) are particularly susceptible to brown edges caused by overwatering because they require consistently moist soil. As you may have noticed, if the soil dries out too much, the plant wilts dramatically. For most houseplants, however, it's a good idea to let the soil dry out somewhat between waterings. If the edges of new leaves are browning, I would suspect overwatering.
Salt burn occurs when various mineral salts, from water and fertilizers, build up in the soil over time. Browning usually occurs on the old leaves first. The excess salt accumulates in the leaf edges, where it kills the tissue and the leaf dries out and turns brown. To prevent this from happening, water plants deeply and slowly. Then, about once a month, flush accumulated salts from the soil by watering plant thoroughly, letting excess drain, and watering again. Similar symptoms occur when too much fertilizer has been applied, or when the fertilizer wasn't properly diluted. Always water plants thoroughly before applying fertilizer to help prevent burn.
Finally, very dry air -- a common problem in heated homes in the winter -- can cause brown leaf edges. Try increasing the humidity around the plant by placing it on a tray filled with pebbles and water -- make sure the plant isn't sitting right in the water. As the water evaporates, it will increase the humidity around the plant."
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Q. My hibiscus houseplant isn't doing well. The leaves look sickly, and I've noticed some little white bugs and what look like spider webs on the top. What is wrong, and what should I do?
- L. A., Eastampton, NJ
A. "Based on your description, I suspect you may have several pests at work. Spider mites produce fine webbing, usually on the new growth or on the undersides of leaves. They suck plant juices, causing the leaves to look discolored or stippled with tiny specks. The mites themselves are tiny and hard to see. Aphids are softbodied, oval-shaped sucking insects and tend to congregate at the growing tips of the plants. They come in a number of colors, usually greenish, reddish or brownish. Whitefly is another possible pest. These small bright white flying insects that looks like a pale version of the fruit fly and moves very fast, swarming up when the plant is disturbed. Finally, mealybugs are another common pest. These insects form cottony-looking masses in the leaf axils.
These are all common pests on hibiscus, as well as other houseplants, and (luckily) can be battled the same way by using insecticidal soap according to the instructions on the label. Be sure to reapply at the indicated intervals to control subsequent generations of the pests. In the meantime, also pick off any dried up foliage. In summer, bring the plant outdoors and hose it off frequently to help dislodge pests."
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Q. I was told I have scale on several of my houseplants. What can I use to control it?
- B. S., Pullman, WA
A. "The small brown discs attached to stems and the undersides of leaves are scale insects. The adult females have a waxy outer shell that protects them and makes it difficult for insecticides to reach them. You can wipe the scales off with a damp cloth or push them off with a Q-tip. After you've removed them all, spray the entire plant with a light summer oil to suffocate any remaining immature scale insects. Follow the label directions closely when applying.
When you bring new plants into the house, it's always safest to isolate them from the rest of your collection until you're sure they're not harboring any insect or disease problems."
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Q. Is there anything I can use in or around my houseplants to keep my cat from chewing them?
- K. D., Hartford, CT
A. Try growing some grass just for your cat to eat. Many cats love to chew on grass. (Perhaps it aids in digestion.) They love oat grass, wheat grass, barley, etc. You can buy little containers at pet stores. Or buy the un-sprouted grain at natural food stores. Plant it in a soil less seed starting mix, keep moist, and place in sun. With a little training and encouragement, most cats can learn that the grass is theirs; the spider plant is yours!
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