Cooperative Extension Publications

Tips for Growing Houseplants in Maine: Caring for Houseplants in Maine (PDF)

Tips for Growing Houseplants in Maine: This newly revised and expanded fact sheet series addresses the basics of keeping houseplants. It will help you diagnose common problems with your houseplants, such as insects and diseases; overwatering or underwatering; improper lighting, temperature, or humidity; and insufficient pot size (root-bound). The series addresses how to start new plants from old plants, and also the unique challenges of growing houseplants in Maine, including the use of artificial light.

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Adapted by Donna Coffin, Extension Professor, University of Maine Cooperative Extension

Reviewed by Rebecca Long, Extension Professional, Matt Wallhead, Extension Ornamental Horticulture Specialist, and Alicyn Smart, Extension Plant Pathologist, University of Maine Cooperative Extension

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Houseplants can become infested with several kinds of insects and mites that thrive in the favorable temperature and growing conditions of the average home. High temperatures and a large group of plants are particularly favorable to most insects.

Prevention of Insect and Disease Infestations

• Healthy plants will be less susceptible to infestation. See Bulletin #2611, Caring for Houseplants in Maine.
• Examine plants, including the underside of leaves, for disease, insects, eggs, webbing, or feeding damage before purchasing. It’s a good idea to isolate new plants for a month; control infestations if necessary.
• Regularly inspect your plants as you water. Controlling a few insects is much easier than controlling a large infestation.
• Once every three to four months, wash all your plants with warm soapy water and a soft cloth to remove any built up dust. Hairy textured leaves like African violets can be brushed with a soft brush to remove dust. A regular bath may be all that is needed to remove many insects. Use two teaspoons of a mild liquid dishwashing detergent to one gallon of water. Keep the soap mixture out of the soil.
• Use sterilized soil for potting to prevent development of soil insects.

Insecticides

Before spraying a plant with an insecticide, make sure you know what the insect is (Table 1) (University of Maine Cooperative Extension Insect Lab) and follow the label directions very carefully. Consider removing the infected leaves or discarding infested plants rather than treating them with a toxic substance.

Move the plants to be sprayed into a well-ventilated area, such as the garage, basement, or a room with a fan. If the weather allows, treat plants outdoors and away from direct sunlight. Bring plants back in when dry.

Note: Check all pesticide labels carefully. Products may not be registered for use on all varieties of plants or may not be tested on all rare or unusual varieties. If the host and pest are not listed on the label, do not use the pesticide. Systemic pesticides, such as imidacloprid (BioAdvanced 2 in 1 Plant Food and Insect Control Spikes or Bonide Systemic Houseplant Insect Control), work by being absorbed into the plant, via the roots, and are ingested by pests when they feed on the plant. Systemics should not be used in combination with beneficial insects.

Table 1: Common Houseplant Insects and How to Control Them
(Adapted with permission from Preventing, Diagnosing, and Correcting Houseplant Problems from Penn State University.)

Pest	Photo	Description	Damage	Control
Aphids	J. Dill	Tiny green, brown, or black insect, located on the undersides of leaves	Feeding damage causes stunted plant growth and curled or distorted foliage	Wash off with water, insecticidal soap,or neem, or use imidacloprid
Fungus Gnat	C. D. Armstrong	Adult is a small fruit fly–type insect. Larvae is a small white worm or maggot that lives in the moist soil	Minimal damage	Allow the soil surface to dry between waterings or use Bacillus thuringiensis subsp. israelensis
Mealybugs	US National Collection of Scale Insects Photographs, USDA ARS, Bugwood.org	Scale insect with white cottony appearance on stems, undersides of foliage, and on nodes (where the leaf or bud attaches to the plant’s stems)	Feeding damage causes stunted plant growth	Wipe off with cotton swab dipped in alcohol, or use insecticidal soap, or neem,or use imidacloprid
Mites: Spider	J. Dill	Microscopic light-colored arachnids (not insects)	Produce webbing on foliage and stems	Discard heavily infested plants; or horticultural oil (can cause damage)
Mites: Cyclamen	Jody Fetzer, Maryland National Capital Park and Planning Commission, Bugwood.org	Microscopic arachnids not visible without magnification	Feeding produces distorted yellowish foliage	Discard heavily infested plants or use insecticidal soap[1]
Scale	Whitney Cranshaw, Colorado State University, Bugwood.org	Oval or round brown insects located on stems and leaves	Insects suck plant juices, resulting in poor or stunted plant growth. Black fungus may grow on honeydew (sap) excreted.	Discard heavily infested plants; wash off with water, wipe off with cotton swab dipped in alcohol, or use insecticidal soap, neem oil, or horticultural oil (can cause damage)[2]
Springtails	J. Dill	Minute in size (1/8th to 1/16th of an inch in length), dark-colored but some can be white or light in color. Live in moist soils.	They are beneficial insects because they feed on fungi, pollen, algae, and decaying organic matter.
Thrips	J. Dill	Extremely tiny (1/8th to 1/4 inch) insects. Adults are light tan to dark brown; appear white when young	Feed on foliage and flowers, causing them to have a silvery appearance and become distorted and discolored	Use neem, horticultural oil, spinosad,or pyrethrins
Whitefly	Frank Peairs, Colorado State University, Bugwood.org	Small, white, gnat-like insect	Adults and young feed on leaves, causing the leaves to turn pale yellow or white	Wash or use alcohol swab; insecticidal soap, or neem, or use imidacloprid

[1] Bessin, R. 2019. Cyclamen Mite in the Greenhouse. University of Kentucky College of Agriculture https://entomology.ca.uky.edu/ef422

[2] Klass, C. 2012. Scale on Houseplants. Cornell University http://idl.entomology.cornell.edu/wp-content/uploads/Scales-on-Houseplants.pdf

Table 2: Chart of Pesticides, active ingredients, brand names
Mention or display of a trademark, proprietary product, or firm in text or figures does not constitute an endorsement and does not imply approval to the exclusion of other suitable products or firms.

Active Ingredient	Trade Name(s)
Bacillus thuringiensis subsp. israelensis	Gnatrol, Knox-Out Gnats
Neem oil (Clarified hydrophobic extract of neem oil)	NimBioSys Neem Oil, Bonide Captain Jack’sNeem Oil
Insecticidal soap (potassium salts of fatty acids)	Bonide Insecticidal Soap Multi-Purpose Insect Control, Garden’s Alive! Plant Guardian Houseplant Insecticidal Soap, or Safers Insect Killing Soap
Imidacloprid	BioAdvanced Fertilizer with Imidacloprid plant spikes, Bonide Systemic Houseplant Insect Control
Horticultural oil (mineral oil)	Bonide All Seasons Horticulture and Dormant Oil, Safer Brand Horticulture and Dormant Oil Spray
Spinosad	Bonide Spinosad Concentrate (AKA Captain Jacks Deadbug Brew), Gardens Alive! Bulls-Eye Bioinsecticide, Monterey Garden Insect Spray
Pyrethrins	Bonide Pyrethrin Garden Insect Spray, Gardens Alive! House Guardian Insect Spray, Safer Brand End All Insect Killer

 

Table 3: Houseplant Disorders and Diseases
(Adapted with permission from Preventing, Diagnosing, and Correcting Houseplant Problems from Penn State University.)

Abiotic (environment)[1]
Symptom	Photo	Common Cause
Spindly plants / leggy growth/ weak growth	Julie Weisennhorn, UMN Extension	Not enough light intensity or length of time in the light See Bulletin #2614, #4 Growing Houseplants Under Artificial Lights in Maine. Root system damaged from being kept too wet
Few flowers	R. Long	Poor lighting conditions
Yellowing leaves	R. Long	Overwatering Not enough light Relative humidity is too low Soil drains poorly and remains wet for too long Injured by low temperatures resulting from a draft caused by an open door, window, or air conditioner Natural senescence (aging) of older leaves (normal process) Lack of nitrogen
Leaves sun-scorched/ sunscalded	Tina Smith – UMass Extension, RetiredD. Coffin	Receiving too much direct sun
Brown leaf tips	A Smart R. Long	Chemical burn from overapplication of pesticide or fertilizer Soft water Soil remains dry for extended periods of time Temperature is too low
Small leaves	R. Long	Soil remains either too wet or too dry Lack of proper nutrients
Wilting plant	Photo courtesy of University of Wisconsin-Madison	Soil remains either too wet or too dry

Biotic (disease organism)[2]
Name	Photo	Organism	Symptom	Management
Anthracnose	Photo courtesy Margery Daughtrey, Cornell University	Colletotrichum and Gloeosporium fungi	Leaf tips turn yellow, then brown; entire leaf may die	Remove infected leaves and avoid misting leaves
Leaf spots	R. Long	Fungi and bacteria	Fungal: Leaf spots appear brown and may have a yellow halo; tiny black dots (fungal bodies) can be seen with a magnifying lens on the brown tissue; portions of or the entire leaf may die Bacterial: Leaf spots appear water-soaked and may also have a yellow halo	Remove infected leaves; increase air circulation; avoid getting water on leaves
Powdery mildew	B. Watt	Fungus Oidium genus	White powdery fungal growth on foliage; leaf distortion; leaf drop may result	Increase air circulation around plant; avoid saturated soils; remove severely infected foliage
Root and stem rots	D. Coffin	Botrytis species (sp.), Pythium sp., Alternaria sp., Phytophthora sp., Sclerotinia sp., and Rhizoctonia sp.	Brown to black soft or mushy roots or lack of roots; girdled soft stems with a brown or black lesion near the soil line; plants wilt, show nutrient deficiency symptoms, and may eventually die	Cut back on watering; dispose of infected plants and sterilize any pot that will be reused

[1] Kelly, K. 2016. Preventing, Diagnosing, and Correcting Houseplant Problems, Penn State University, https://extension.psu.edu/preventing-diagnosing-and-correcting-common-houseplant-problems

[2] Kelly, K., Preventing, Diagnosing, and Correcting Houseplant Problems, Penn State University, https://extension.psu.edu/preventing-diagnosing-and-correcting-common-houseplant-problems

Additional Resources

• Bulletin #2611, Caring for Houseplants in Maine
• Bulletin #2612, Dealing with Houseplant Problems in Maine
• Bulletin #2614, Growing Houseplants Under Artificial Lights in Maine
• Bulletin #2615, Creating New Plants from Old Plants
• Bulletin #2516, FAQ About Houseplants in Maine

Sources

Houseplants in Maine by Lois Stack, Ornamental Horticulture Specialist, University of Maine Cooperative Extension

House Plant Tips by Gleason Gray, Extension Educator, Penobscot County, University of Maine Cooperative Extension

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Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

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