Plant care guide
Do Spider Mites Affect Boston Ferns? Signs and Safe Fixes
Updated
Why does my Boston fern have spider mites?
Yes, spider mites do attack Boston ferns, mostly when the air around the plant is too dry. Look for fine pale speckling and a faded, dusty look on the leaflets, tiny moving dots underneath, and fine webbing in heavier infestations.
What to do first
Raise the humidity around the fern and rinse the fronds, undersides included, with a gentle but brisk spray of water. Ferns are sensitive to many pesticides, so test any product labeled for houseplants on a few fronds first and let it dry out of direct sun.
A Boston fern that turns dull and dusty-looking can be hard to read. Spider mites are one real cause. NC State Extension says scales or spider mites can be a problem on Boston fern when the air around the plant is too dry. Clemson’s indoor ferns factsheet calls scale insects and mites the most common insect problems of ferns. The treatment needs a lighter touch than on most houseplants.
Confirm it is spider mites
Clemson HGIC’s houseplant pests factsheet says mites are so small that damage is usually the first sign. Look for:
- Light speckling on the leaflets (pinnae) and an overall faded look.
- Bronzed or yellowed leaflets if the mites go unchecked.
- Silky webbing among the leaflets in heavier infestations.
- Tiny moving dots on the undersides. UC IPM says a 10× hand lens shows them easily (UC IPM: Spider Mites).
UC IPM suggests shaking a frond over white paper and watching for specks that move. Be sure mites are present before you treat.
Rule out look-alikes
- Spores. NC State notes that Boston fern produces spores on the underside of the leaflets as dark brown to black dots in a pattern, and warns not to mistake them for insects. UW–Madison describes them as two rows of round sori near the leaflet margins (UW–Madison: Boston fern). They do not move.
- Scale. Fern scale males are snow-white and ridged, and females are flat and brown, says NC State’s fern scale factsheet. They stay put, unlike mites.
- Dry-air browning. UW–Madison says the tips and edges of the leaflets may brown in dry interiors, especially in winter. That browning has no speckles or webbing; see Boston fern brown fronds.
Why sprays need care on ferns
Clemson’s fern factsheet says pesticide sprays injure many ferns. It advises reading the label carefully, testing on a small area first and watching for injury. NC State calls ferns notoriously sensitive to pesticides. University of Maryland Extension says ferns are sensitive to many ingredients, though horticultural oil can be tolerated if the plant stays shaded while the spray dries (UMD: Scale Insects on Indoor Plants).
Clemson HGIC 2252 lists maidenhair fern among the plants that should not receive insecticidal soap. Boston fern is not on that list, but the general fern warning still applies.
What to do
- Isolate the fern. Clemson makes this the first step for any houseplant pest.
- Trim the worst fronds. UW–Madison suggests cutting old fronds off at the soil to encourage new ones. Bag the trimmings.
- Rinse with water. Clemson’s fern factsheet suggests removing pests with a brisk water spray outside. Its pest factsheet adds that repeated water sprays help control mites. Clemson also notes fern fronds are sensitive to rough handling, so support them and keep the spray even rather than blasting one spot.
- Raise the humidity. NC State says Boston fern needs high humidity and suggests a kitchen or bathroom, or a tray of wet pebbles. Clemson suggests double potting in moist sphagnum moss.
- Spray only after a test. If rinsing is not enough, test a product labeled for houseplants on a few fronds and wait. Clemson says injury can take at least 48 hours to show. Following UMD and NC State, let any spray dry before the fern sees bright light.
- Repeat and recheck weekly. Clemson says mite control often takes weekly treatment for several weeks.
Pets
The ASPCA lists Boston fern as non-toxic to dogs and cats. Keep pets away from any treatment until it has dried.
Keep mites away
- Keep humidity up in winter. Clemson notes home humidity is very low in winter and ferns need extra attention.
- Keep the mix evenly moist. NC State says it should never dry out. UC IPM links water stress to worse mite damage.
- Quarantine new plants for six weeks, checking undersides weekly, as Clemson advises.
For whole-plant care, see our Boston fern care guide. Our spider mites guide compares treatments across houseplants, and the Boston fern hub lists our other fern pages.
Related guides
Other boston fern problems we cover: fungus gnats, shedding leaflets, yellow leaves, root rot.
References
- NC State Extension Gardener Plant Toolbox: Nephrolepis exaltata
- Clemson Cooperative Extension: Indoor Ferns
- Clemson Cooperative Extension HGIC 2252: Common Houseplant Insects & Related Pests
- UC Statewide IPM Program: Pest Notes: Spider Mites (Publication 7405)
- University of Maryland Extension: Scale Insects on Indoor Plants
- NC State Extension: Fern Scale Insect
- UW–Madison Extension: Boston fern, Nephrolepis exaltata ‘Bostoniensis’
- ASPCA Animal Poison Control: Boston Fern
How this guide was put together: NC State Extension, Clemson Cooperative Extension, UC Statewide IPM Program, University of Maryland Extension, UW–Madison Extension and ASPCA guidance.