Can the Sun Cause Ferns to Brown?

Sun Damage to Ferns

• Many ferns are easily damaged by excess exposure to light and heat. Any fern that is typically found growing on the ground in the full shade of woody, temperate areas, including the Boston fern, tolerates only indirect light as the maximum amount of sunlight it can receive and remain healthy. Direct sunlight, even during cooler parts of the day, is a surefire way to cause brown scorch and scald marks to appear on the leaves of a fern.

Sun-Tolerant Ferns

• Some types of ferns tolerate sunlight very well. These include plants such as the cinnamon fern and the ebony spleenwort, which both tolerate moderate amounts of direct sunlight in their growing environments. The royal fern and southern shield fern also tolerate sunlight, according to the Clemson Cooperative Extension website. These ferns do not brown unless exposed to direct sun during the hottest part of the day. Sun-tolerant ferns grow best in sun to partial or full shade.

Leaf Tip Burn

• If sunlight isn't the cause of browning, other environmental factors such as fertilizer may play a role in the browning of fern leaves. Leaf tip burn is caused by excess fertilizer; fertilizer burns are a garden problem related to synthetic fertilizers that contain salts that dry out the soil and flesh of plants. Spreading too much fertilizer around a fern prevents the plant from utilizing the nutrients properly and leads to brown leaves on the plant.

Rhizoctonia Blight

• Rhizoctonia solani is a fungal disease that causes browning of fern leaves. Spots begin near the top of the fern and spread rapidly to cover leaves. Fungal webs sometimes form and spread between the leaves of the fern plant, leading to further damage and browning of the leaves. Rhizoctonia blight of ferns is treatable with fungicide sprays that contain the chemical thiophanate methyl. Remove and destroy any severely damaged leaves.