What Causes the Fronds on a Boston Fern to Turn Yellow or Brown?

Pythium

• Boston fern plants that are affected by pythium root rot will have signs of graying fronds and then yellowing fronds, as well as stunting and wilting. If you see the graying fronds, you need to check the roots of the plant for rot. If the root rot isn’t controlled, the fronds will yellow and the plant will eventually die. Some Boston ferns can be saved by repotting in a sterile potting soil or using a chemical formulated to treat pythium root rot. Water the soil and allow it to dry at least 2 inches deep from the surface before watering the plant again.

Humidity

• Boston ferns need medium to high humidity. If the humidity around the plant is low, the fronds will start to yellow. Assuming the fronds are yellowing because of low humidity, you can fill a drainage tray with gravel and place it under the plant container. Each time you water the plant, the runoff will drain into the tray and humidify the air around the plant.

Runner or Leaf Tip Burn

• The tips and runners of the Boston fern will turn brown if the plant soil has high rates of soluble salt. If the leaf tip or runner burn is allowed to continue without control, the entire frond will turn brown and die. You can leach the salts from the soil by placing the plant under a faucet and running water through the soil for about 5 minutes. Salt comes from months or years of fertilizing the plant or from using water that is filtered through a water softener.

Care and Environmental Issues

• If the plant doesn’t have root rot, low humidity issues or leaf tip burn, it could be the care that is causing the fronds to turn yellow. Boston ferns do well in low-light conditions, but if the fronds turn light green and start yellowing, the plant isn’t getting enough light. Less than ideal temperatures will also cause the frond to turn yellow. The best temperatures are 95 degrees F or less during the day and about 65 degrees F at night.