By Jessica Carlson

Otter Tail County Master Gardener Intern

The outdoor gardening season is ending, and the Holidays are right around the corner. Many gardeners have brought in their plants from the patio after summer vacation. Sadly, uninvited guests often come along for the ride. Tiny insects can thrive in the warm, sheltered environment of our homes, and understanding their habits can help keep houseplants healthy all winter long. I have made a list of few unpopular guests.

The aphid is like an overenthusiastic uncle arriving at dinner in a SUV full of his children. Aphids are soft bodied insects that suck plant sap and reproduce quickly. They often cluster on tender new growth or under leaves. Sticky honeydew and distorted leaves are common signs. A strong stream of water can wash them off, and insecticidal soap helps control heavier infestations. Check plants weekly because aphids multiply fast in warm, still air.

Fungus gnats are freeloaders that appear suddenly and begin to make themselves at home.

They are tiny black flies that hover near soil surfaces. Their larvae live in moist soil and feed on decaying matter and tender roots. Adults are more annoying than harmful, but larvae can damage seedlings and delicate roots. Letting the top inch of soil dry before watering reduces their numbers. Yellow sticky traps catch adults, and a soil drench of Bacillus thuringiensis israelensis can target larvae if needed.

Spider mites leave a mess behind while staying out of sight. They are common when indoor air becomes dry. They are invisible to the eye but leave fine webbing on the undersides of leaves. Leaves may appear stippled or bronze as they lose chlorophyll. Mites thrive in low humidity and warm rooms, so misting plants or running a humidifier can help discourage them. Rinsing leaves in the sink or shower and using insecticidal soap or neem oil can also help.

Mealy bugs are overly dependent on their host. These slow-moving insects covered with white cottony wax, often hide in leaf axils, along stems, or on roots of potted plants. They suck plant sap, causing yellowing and leaf drop. Removing them with a cotton swab dipped in rubbing alcohol is an easy first step. For larger infestations, insecticidal soap or neem oil can be effective if applied thoroughly and repeatedly.

Scale is the couch surfing cousin. These insects look like small brown or gray bumps attached to stems or leaves. They do not move once settled but feed continuously on plant sap and produce sticky honeydew. Scraping them gently with a fingernail or soft brush removes a majority of them. Heavier infestations can be treated with horticultural oil, which suffocates both adults and young crawlers.

Pests thrive when growing conditions are less than ideal. Overwatering keeps soil damp enough for fungus gnats and root rots. Underwatering weakens plants, making them more vulnerable to spider mites and aphids. Low humidity encourages mites and slows plant recovery. To keep conditions balanced, try inexpensive moisture meters to monitor soil moisture and hygrometers to track indoor humidity levels. Humidifiers, pebble trays, and proper air circulation help create a healthier environment for plants.

If a pest problem occurs, it is best to quarantine the affected plant away from your others until it has been treated and the pest is fully controlled. This helps prevent insects from spreading throughout your home. Inspecting houseplants weekly and isolating new or infested ones makes a significant difference. Healthy plants resist pests more effectively, so paying attention to watering, light, and humidity will help keep both your plants and your winter spirits thriving.

For more information on preventing and controlling houseplant pests visit the University of MN Extension www.extention.umn.edu/product-and-houseplant-pests/insects-indoor-plants