Fern Diseases

Ferns are not typically susceptible to most common garden diseases. This easy-to-care-for plant thrives in most garden settings as long as the soil is very well draining and there is shade during part or most of the day. Growing a fern in inadequate conditions will result in a weakened plant much more likely to contract certain fungal diseases that are present in most garden soils.

Tip Necrosis

Tip necrosis is more a cultural problem associated with the under or over-watering of ferns. Garden-grown ferns that are allowed to dry between waterings may start to show stress at the tips of their fronds. Eventually, the whole frond could turn brown and die back if the plant is left unwatered or not moved to a better location with sufficient drainage.

Container-grown ferns outdoors or in the house can also show signs of tip necrosis as a result of low humidity. Browning of fronds also occurs at the end of the growing season for those types that are fully herbaceous and go dormant through the fall and winter. This is completely normal with no treatment required. 

Identifying Tip Necrosis

The tips of the fronds begin to yellow and eventually turn brown and crispy. The whole frond may eventually be affected when left untreated.

Treating Tip Necrosis On Ferns

Snip off the ends of any fronds that are crispy, making sharp cuts just above a node of l Resume proper watering if the cause is underwatering. Overwatered plants need to have all affected plant material removed and replanted in a better-draining location. Container-grown plants will need to be repotted into fresh potting mix and a better-draining container and then allowed to dry for a few days before resuming a watering schedule. 

Fungal Leaf Spot

Fungal leaf spot fungus is present in garden soils and often becomes active in growing seasons that are wetter and colder than normal.  Heavily covered fronds will dieback slowly although as long as only a few fronds are affected the plant will survive and produce new growth throughout the summer.  Herbaceous ferns will regrow fresh fronds the following growing season.

Fungal leaf spot is mostly cosmetic only causing growth issues in plants that are very young or very weakened by not growing in their preferred conditions. 

Identifying Fungal Leaf Spot

Small brown or black spots will appear on both the top and bottom of the fern fronds. Fungal leaf spots are not typically raised or in even distribution on the underside of the fronds like the spore-producing sporangia. As the fungal leaf spot spreads whole fronds will look like they are covered in brown or black blotches.

Treating Fungal Leaf Spot On Ferns

Removal of the affected fronds is recommended as soon as the disease is diagnosed. Mulching with organic compost or finely shredded arborist chips helps to keep developing fronds above the soil and reduces the amount of soil splashing on the plant during watering. Reduce overhead watering during periods of cool and damp weather when fungal leaf spot spores have the best chance of spreading. are most active. 

Crown and Stump Rot

Crown and stump rot is often thought of as appearing suddenly on plants, when in fact the damage that is seen on the top growth may have been developing over the course of many growing seasons below the soil. The fungal spores that trigger crown and stump rot diseases are always present in garden soil but only become a problem when plants become weakened by some other cause.

Overwatering and planting ferns too deep in the soil are the two most common situations that crown and stump rot fungus take advantage of. 

Identifying Crown and Stump Rot

The top growth of fronds declines suddenly. Further investigation will reveal issues with the root system as well as black and rotten parts of the fern crown (where the new fronds emerge). The garden soil may be waterlogged and boggy or even have a rotten smell from the lack of air space in the soil.

Treating Crown and Stump Rot On Ferns

Remove the plant and either replant it in a different location or fix any drainage issues with the garden bed. Replant the fern so that the crown (where the fronds emerge) is above the soil level by an inch or more. This helps to keep air flowing around the crown of the plant. Do not pile mulch on or against the crown of the fern and use drip irrigation or soaker hoses to keep water from collecting in the crown and sitting for long periods.

Damping Off

Damping off is a fungal disease that afflicts new seedlings. Both water molds and soil-born fungi are to blame for damping off and can cause sudden death in whole trays of seedlings. Fern seedlings (prothallus)  are particularly susceptible to damping off as they need an atmosphere that is warm and high in humidity, just the conditions that favor outbreaks of damping off. 

Identifying Damping Off

New seedling stems will begin to show areas of black where they touch the soil and appear to have a very tapered shape. As the fungus takes over the seedling, stems topple over and the spores begin to grow a white fuzzy coating across the soil surface. This can quickly take over whole trays of seedlings within a few days if left unchecked. The seedlings are a complete loss and will need to be regrown in clean containers and fresh seed starting mix. 

Treating Damping Off On Ferns

Never use outdoor garden soil for starting seeds. Native garden soil has fungi and bacteria that happily coexist outdoors with no consequence but when exposed to high humidity and moisture can run amok. Always clean containers, tools, and trays that you are using for seed starting. The damping off fungi survive for a long time on exposed surfaces.

Do not allow the soil to be cold when it is wet, keep plants warm with bottom heat mats if required for growth. Set grow light timers for 12-16 hour cycles to ensure quick growth of the tender new shoots. Do not fertilize plants until they are ready to be up-potted into larger cells or individual pots. Newly germinated seedlings survive off the nutrition in their seed until well after the first true leaves emerge. 

Fern Disease Chart

Sources: “Growing Ferns” Extension Bulletin 737, University of Georgia Extension. wwwextension.uga.edu