Short answer
Your Boston Fern has a spider mite infestation, which is common when indoor humidity levels drop below the fern's preferred high-moisture threshold. The most effective fix is to physically rinse the fronds and maintain consistent humidity above 50% to prevent re-infestation.
Boston Ferns (Nephrolepis exaltata) are notoriously sensitive to dry air, making them magnets for spider mites. While these pests appear as fine webbing and leaf stippling, this is a serious condition that can rapidly cause the delicate fronds to wither and die if not addressed immediately.
Spider mites thrive in the dry, stagnant air conditions often found in homes during winter. They pierce the frond cells to feed on sap, which creates the telltale speckled look and fine, silken webbing.
Check: Hold a piece of white paper under a leaf and tap the frond; look for tiny, dust-like moving specks on the paper.
Fix: Isolate the fern and give it a thorough shower with lukewarm water, ensuring you spray the undersides of the leaflets, then apply neem oil or insecticidal soap every 5-7 days for three weeks.
Boston Ferns require high ambient humidity. When the air is too dry, the plant becomes physically weaker and loses its natural resistance to pests like mites, which actively prefer these stressed conditions.
Check: Check if your home humidity levels are below 50% using a hygrometer.
Fix: Group your fern with other plants, place it on a pebble tray filled with water, or run a humidifier nearby to create a consistently damp microclimate.
While not causing webbing, heavy fertilizer buildup or severe deficiencies can sometimes cause leaf yellowing that mimics stippling. However, this will not produce the silk-like threads associated with active pest activity.
Check: Inspect the leaf undersides closely; if there are no webs or moving pests, check your fertilizer schedule and soil salinity.
Fix: Flush the soil with distilled water to remove excess mineral salts and switch to a balanced, diluted liquid fertilizer used at half-strength during the growing season.
When to worry
You should treat this as an emergency immediately upon spotting the webbing, as Boston Ferns are too delicate to survive heavy mite feeding for long.
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Diagnose my Boston FernYou can remove heavily damaged fronds to reduce the mite population, but the pests are likely still present on remaining fronds and nearby surfaces, so you must treat the entire plant.
Indoor heating systems significantly drop household humidity, creating the exact dry, arid environment that spider mites thrive in and that your fern despises.
Moving it to a bathroom with a window is an excellent strategy, as the daily use of the shower provides the consistent, high-humidity environment that keeps Boston Ferns healthy and mites at bay.
Consistent with guidance from: Royal Horticultural Society, University of Florida IFAS Extension.