Continuing Education and
Communication Services
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
12/10/01
Contacts:
Brooke Edmunds, Department of Plant Pathology, (515) 294-1741, bedmunds@iastate.edu
Del Marks, Continuing Education and Communication Services, (5150 294-9807,
delmarks@iastate.edu
Yard and Garden Column for week beginning Dec. 14
Warding Off Houseplant Problems
By Brooke Edmunds, Research Assistant
Department of Plant Pathology
Iowa State University Extension
As the weather turns colder, many gardeners turn to houseplants to get their green thumb fix. The first step to healthy houseplants takes place at the store. The best places to buy houseplants are nurseries or garden centers. Choosing to shop at stores that specialize in plants usually means that you'll get the plants of the most consistent quality. Look around at all the plants; do they generally look healthy?
The foliage should be free of spots, brown leaf edges, and insect pests. Check the roots as best as you can; it's often easy to pop a root ball out of its flat or pot if you don't mind getting your hands a bit dirty. Are the roots on the outside of the ball a bright white color? That's what you're hoping for. If the roots are brown and slimy-appearing, leave the plant on the bench. The best plants in the store are usually going to make the best plants at home.
If you're like me, every once in a while you'll bring home a "pity plant." A good example is the beat-up, brown-tipped ivy on the half-price sale rack. You're convinced it will recover if it's only given a good home. Try to resist the temptation! Pity plants usually die from the stress they suffered in their early stages; no matter how much love and nurturing they receive.
Sometimes, however, even the healthiest looking plants start to decline once you bring them home. Instead of giving up, ask a few questions. Did the plant get too cold in the car on the way home? Did you forget to water it over the Thanksgiving holiday? Have your cats discovered an alternative to the more traditional litter box?
The best way to keep plants healthy once you bring them home is to provide a stress-free environment. The first test a new houseplant faces is the change in environment. Growing conditions in greenhouses are nearly perfect, while houses tend to be dry and dark in winter. Many people tend to overwater houseplants, so that the soil is wet all the time. If you were a plant, you'd complain too about being trapped in a dark, dry room with wet feet!
Maybe the most common source of houseplant woes in Iowa is buildup of salts in the pot. The salts come from minerals in the tap water most people use on their plants. When the water evaporates, the salts are left behind, and can gradually accumulate to the point where the roots get burned. Browned leaf tips and edges often indicate an excess-salts problem. Fortunately, salt buildup can be remedied. Just flush the pot with at least five times its volume of water, which will wash out most of the salts.
Houseplants also can have problems with diseases and insect pests. At times it's difficult to tell if poor growing conditions or pests are hurting a plant, as symptoms tend to mimic each other. The four most common disease and pest problems of houseplants are powdery mildew, leaf spots, root rot, and mites.
Powdery mildew usually shows up as gray or white growth on surface of leaves. It's most common in crowded, shaded, or humid environments. This fungal disease thrives under cooler temperatures and humid conditions. African violets, jade, begonias and others seem most susceptible to this disease. The best way to manage powdery mildew is to reduce humidity and increase air movement by keeping plants in well-ventilated areas and avoiding overcrowding.
Bacteria, fungi, insects, accidental chemical exposure, or poor growing conditions can cause leaf spots, making this sort of problem the most difficult type to diagnose correctly. Depending on the culprit, the spots can vary from pinprick-size brown spots to large spots that take over the entire leaf. Since it can be difficult to diagnose the cause of leaf spots, try removing the affected leaves and avoid getting the leaves wet when watering.
Overwatering is the main reason root rot develops. Roots struggle to breathe in soil that is kept wet all the time. On the other hand, certain fungi such as Pythium, love moist soils and are only too happy to feast on roots weakened by waterlogging. Root rots reveal themselves aboveground as wilting of the foliage and belowground as brown, mushy roots. If you notice the problem early, you may be able to reverse the damage by cutting back on your watering regime and allowing the soil surface to dry between waterings. Emergency intervention, in the form of repotting the plant in a better-drained mix, can sometimes be effective too.
Spider mites can be an extremely annoying pest of houseplants. This tiny insect-like animal (you'll have to squint or use a magnifier to see this one) feeds on leaves, causing a yellow blotchy appearance. If spider mites are abundant, fine webbings will be visible over the yellowed leaves. For light infections, you may use ordinary dishwashing detergent as an insecticide with little risk of injury to plants.
To make your own insecticidal soap spray solution, mix 1 tablespoon of liquid dishwashing detergent in 1 quart of water. Soap sprays have no residual activity and only control mites that are contacted directly. Thorough spraying, especially to the undersides of leaves is important for control. Heavily infested plants are most likely a lost cause and should be discarded.
This is only a sampling of the most common houseplant problems. Since there are so many species of houseplants, it's impossible to list all the potential maladies. If your plants are suffering, your best bet is to call the ISU Hortline at (515) 294-3108 for advice on growing conditions and other stresses. For more troublesome problems, send a sample for diagnosis to your county extension agent or the Plant Disease Clinic, 351 Bessey Hall, Iowa State University, Ames, IA 50011.
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ml: isugarden
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