Ferns are warm season plants that cannot withstand cold temperatures. If a fern is showing signs of dying, it could be related to many different causes, including temperature, moisture, light, humidity and soil or container conditions. Without the proper care and conditions, the ferns will start to die.
Ferns such as staghorn and brake ferns can handle slightly cooler night temperatures than the Boston fern, which needs night temperatures at about 62 to 65 degrees Fahrenheit. Daytime temperatures should be between 68 and 72 degrees Fahrenheit. If plants are grown outdoors as container plants, you must bring the plant indoors before the night temperatures drop down into the 50s.
Moisture and Fertilizer
Ferns need moist soil, but not soggy soil. Ferns such as holly, brake and rabbit's foot ferns need water when the surface of the soil is dry. Other ferns types may require more water to keep the soil moist to slightly damp. If the fern has brown tips, it could be a lack of moisture or humidity. Although ferns don't need fertilizer, if you are adding fertilizer, only add it to the soil once a month, diluted by one-half.
Ferns require high humidity that mimics the rainforests where the plants grow wild. Boston ferns, staghorn and maidenhair ferns are especially prone to dying without high humidity. You can add humidity around the plant by placing the container in a drainage tray filled with gravel to catch the excess water runoff during watering. If the plant needs more humidity, add water directly to the drainage tray.
Soil and Container
Soils for ferns must have good drainage. If the roots are kept on the wet side, the fern will start to die back. A good medium to use is peat moss or 1 part sand and 3 parts peat moss. The roots must be moist, but not wet. If the fern becomes rootbound, it will start to show signs of stress. Ferns don't like to become rootbound like some other plants. If the fern is old and has been in the same container for a long time, you may need to repot it into a container 2 to 3 inches larger than what it is planted in currently. If you have an air fern, these plants grow without soil. The plant gets its nutrients from the water and air.
If you have a fern with pests such as mites, mealybugs or scales, you cannot use any pesticide or it will damage the fern. Ferns that have a pest problem can be tended by removing the pests by hand or by using a hard mist of warm water to dislodge the pest. If the fern is heavily infested and a pesticide is needed, you must be very careful and follow the directions for treating ferns.