Plant care guide
Boston Fern Brown Fronds: Dry Air, Dry Mix, Sun or Salts?
Updated
Why are my Boston fern fronds turning brown?
Brown, crispy Boston fern fronds usually trace back to dry air, a root ball that dried out, direct sun, or salts from fertilizer and hard or softened water. Where the browning starts, and which fronds it hits, tells you which one to fix.
What to do first
Check the mix first: if it has dried out, water it through. Then check the spot for heat, dry air and direct sun, look for a white crust of salts, and cut the dead fronds back once new growth appears.
Brown fronds on a Boston fern (Nephrolepis exaltata) look alarming, but the plant is rarely dying. The browning is a record of stress the fronds have already been through. Brown tissue will not turn green again, so the goal is to find the cause and protect the new fronds.
NC State Extension says this fern needs high humidity and moist soil that should never be allowed to dry out. Most brown fronds come from one of those two slipping, from too much sun, or from salts in the mix.
First, rule out spores
Look under a frond before you change anything. NC State says Boston fern makes spores on the underside of the leaflets, as dark brown to black dots in a regular pattern. It warns not to mistake these for insects or disease. Neat rows of dots on otherwise green leaflets need no treatment.
Read where the browning starts
| What you see | Likely cause | Source |
|---|---|---|
| Tips and edges of leaflets brown, worse in winter, mix moist | Dry indoor air | UW–Madison, Clemson, UConn |
| Whole fronds or patches crisp, mix dry and pulling from the pot | Root ball dried out | Clemson, NC State |
| Browning starts at frond ends and works back, after feeding | Too much fertilizer | UMN, UW–Madison |
| White or grey crust on the mix or pot rim, brown tips | Salt buildup | Clemson |
| Bleached or scorched fronds on the window side | Direct sun | Clemson, UConn |
| Brown tips on a basket hung near the ceiling or a heater | Hot, dry air | UMN, Clemson |
Dry air
UW–Madison Extension says that in dry indoor air, especially in winter, the tips and edges of the pinnae may turn brown. Clemson’s indoor ferns factsheet says ferns may develop brown leaves or leaflets at low humidity, and that home humidity is very low in winter. UConn lists browning frond tips, and yellowing and dropping of interior leaves, as signs of low humidity.
Height matters too. University of Minnesota Extension warns that the higher a fern hangs, the hotter and drier the air, and that this can turn frond tips brown. Keep baskets away from the ceiling, heat vents and radiators.
A dried-out root ball
Clemson names too much or too little water as the main problems of indoor ferns, and says never to let any fern dry out completely. One missed watering in a warm room can brown a whole section of a hanging basket.
Lift the pot. A light pot and mix shrinking from the sides point to drought. Clemson’s houseplant disorders factsheet adds that a pot-bound plant has too little soil to hold water for all its roots. If this keeps happening, our guide to Boston fern soil drying out covers pot size, mix and position.
Fertilizer and salts
Ferns burn easily. Clemson says ferns leaf-scorch when fertilized too heavily. UMN says over-fertilizing causes browning that begins at the tips and works back into the fronds. UW–Madison advises half-strength feeding every 4 to 6 weeks in active growth, and much less in winter.
Water quality adds salts as well. Clemson says brown tips and margins can come from salt accumulation, and that a white to grey crust on the mix or pot rim is a sign of it. UMN advises against softened water, because repeated use builds up salts that injure roots.
Direct sun
Clemson says never to put ferns directly in a south- or west-facing window, because direct sun damages the foliage. UConn warns that intense south or west sun can dry out or scald fern fronds. NC State recommends bright, indirect light.
What to do
- Water a dry fern thoroughly. Water until it drains, then empty the saucer after a few minutes, as UMN advises. Clemson warns not to let water stand in fern pots.
- Leach salts if you see a crust. Clemson suggests drenching the pot with water periodically to wash salts out, removing crusts and adding fresh mix. Use rainwater when you can.
- Feed less. Half strength, only in active growth, none in winter (Clemson, UW–Madison).
- Raise humidity near the fern. UConn suggests a pebble tray with the pot above the water line, or a room humidifier. UMN finds misting not very effective and prefers humidifiers.
- Move it out of sun and heat. An east window or a spot behind a sheer curtain suits it, UW–Madison says.
- Trim the damage. UW–Madison suggests cutting old fronds at soil level to encourage new growth. Cut fully brown fronds out. Leave partly green fronds until new ones replace them.
When to look further
If the mix stays wet and fronds yellow and brown from the base, check the roots. Clemson links root rot to slow-draining mix and over-frequent watering. Our root rot guide covers what to look for. Fine webbing or speckled fronds point to mites instead; see the spider mite guide.
For year-round care, read the Boston fern care guide. A bright bathroom can help with humidity; see Boston fern in the bathroom.
Related guides
Other boston fern problems we cover: fungus gnats, shedding leaflets, spider mites, yellow leaves, root rot.
References
- NC State Extension Gardener Plant Toolbox: Nephrolepis exaltata
- Clemson Cooperative Extension HGIC 1505: Indoor Ferns
- Clemson Cooperative Extension HGIC 2251: Houseplant Diseases & Disorders
- University of Wisconsin–Madison Extension: Boston fern, Nephrolepis exaltata ‘Bostoniensis’
- University of Minnesota Extension: Growing tropical ferns indoors
- UConn Home & Garden Education Center: Ferns, Indoor Growing
How this guide was put together: NC State Extension, Clemson Cooperative Extension, University of Wisconsin–Madison Extension, University of Minnesota Extension and UConn Home & Garden Education Center guidance.