Why Are My Fern Leaves Turning Brown? | How To Fix It

Ferns are incredibly ancient nonflowering herbaceous plants that come from the diverse class of Polypodiopsida

These beautiful, luscious plants that reproduce by spores, are not known to be invasive and make great houseplants simply for their astounding ability to remove indoor air pollutants.

The following article describes the most common reasons that fern leaves turn brown and what to do about it. 

Why Do Fern Leaves, Turn Brown

The unfortunate browning of leaves, often called necrosis, is caused by environmental factors such as low soil moisture, nutrient deficiencies, or poor climate conditions. These environmental factors cause stress to your ferns leading to problems with brown leaves. 

The yellowing of leaves, or chlorosis, is the most common symptom that precedes leaf browning, so it is always worth being extra vigilant of any changes in your fern’s normal vibrant green colour. 

What Causes Fern Leaves to Turn Brown

Ferns can be finicky, and since they have evolved in very specific habitats, they require those same conditions to flourish indoors. If conditions such as soil moisture levels, nutrient availability, and climate are not correct, then leaves are likely to brown.  

Watering Problems

Inadequate soil moisture levels or the use of unfiltered tap water are the most common causes of browning leaves on fern plants. 

Overwatering

Consistently overwatered ferns will develop brown leaves, predominantly near the bottom of the fern, and have an overall yellow, wilted, and soggy appearance. The soil will also remain damp for prolonged periods.

If severe overwatering has occurred allow the soil to dry for 2 – 3 days, then only water your fern when the topsoil feels dry. In addition, I recommend top-dressing with a 1-inch layer of worm castings since leaching of soil nutrients is likely. 

Underwatering

Underwatering causes severe browning and curling of leaflet edges, typically following signs of wilting and leaf chlorosis. If long-term drought has occurred, the leaves of the ferns will crisp and die. 

To replenish the soil of moisture, water well until it drains from the holes at the bottom of the pot. Then, repeat a couple of times over the next 3 days, which will limit the potential of leaching. 

Since ferns have such shallow root systems, you will need to water them when the topsoil feels or looks dry rather than sticking to a schedule. 

Every time you water, soak the soil thoroughly so that it drains through the bottom of the pot. This ensures that the soil is properly and evenly dampened between waterings. 

If you find that the soil either dries too quickly or retains too much water, it’s probably a good idea to change the soil. It needs to be nutrient-rich but also provide good drainage whilst also retaining some moisture. I use the following mix for my fern soil:

  • 1/3 Loam Garden Soil
  • 1/3 Perlite
  • 1/3 Peat Moss or Coco Coir
  • 1 Pint of Dried Manure
  • ½ Pint of Charcoal
  • ½ Pint of Small Gravel 

Using Unfiltered Tap Water

Tap water can contain hard minerals, salts, and chemical additives like chlorine and fluoride that will build up in the soil. This can cause harm to the fern’s root system, which leads to browning leaves. 

This type of leaf browning usually follows leaf chlorosis and also a period of stunted growth. 

Switch to using only filtered tap water or rainwater. If you suspect a build-up of impurities in the soil it is worth re-potting your fern in fresh soil. 

Alternatively, is also possible to flush the existing soil of impurities by watering 3 – 5 times over 3 days with enough water to fill the container the fern is in. Let it drain completely between flush cycles. 

Nutrient Deficiencies

Soil that is lacking in nutrients is likely to cause browning leaves, most often appearing after signs of leaf chlorosis and stunted growth. Here’s a rundown of the most common types of nutrient deficiencies in fern plants and how the symptoms will present:

Nitrogen (N)

Leaf chlorosis and the browning of older leaves, followed by defoliation. 

Phosphorus (P)

Browning leaf tips are accompanied by the purple discolouration of older leaves. 

Potassium (K)

Yellowing and browning along leaflet tips and margins.

Calcium (Ca)

Brown scorching and uneven leaf chlorosis on the tips of the newest leaves. 

To remedy soil nutrient deficiencies in fern plants I recommend adding a 1-inch top-dress that contains 50% worm castings and 50% compost, then water thoroughly to allow nutrients to leach into the fern’s soil. 

I like to adhere to the recommendation made by the University of Georgia when it comes to fertilizing fern plants. This involves feeding them monthly from spring to fall and every 2 months during the winter with natural fish emulsion fertilizers. These gentle, low NPK types of fertilizers will ensure your ferns get the nutrients they need without burning their sensitive roots.

Climate

Ferns prefer temperatures under 75 degrees Fahrenheit, require relative humidity above 40%, and indirect sunlight from northern windows. 

Low Humidity

Most fern species will begin to brown and crisp on the edges of their leaves if the humidity level is not consistently maintained between 40 – 50%. 

If you need to increase humidity you could try relocating your fern, installing a humidifier in the room or adding a layer of consistently moist sandy gravel to the catch tray of your fern. It also helps to spray your fern with filtered or rainwater daily. 

Keep your ferns away from air conditioners, air vents, or any sources of heat. 

Direct Sunlight Exposure

While ferns are tropical species, they have evolved in the understory where they do not receive direct sunlight. Therefore, brown sun-scorched areas will develop especially on the top of the ferns if left in the sun for more than a few hours. 

To prevent leaf scorching relocate to a northern window or use a sheer curtain to lower the intensity of the direct sunlight. Remove any sunburnt leaves and water well once the fern has recovered. 

Pest, Bacterial, Or Fungal Infection

Ferns don’t typically have pest problems, but when they do, it is devastating to the plant, which will likely perish without quick action. 

Fern Scales

Fern scales are hard-bodied insects that appear as small brown spots on the leaves. Then, honeydew, a sticky substance secreted by the scales, develops brown and blackened fungus that encases the entire fern leaf. 

Inspect the fronds of your fern regularly and remove any leaves that have any signs of scaling or fungal blackening. If the infestation is too severe you may need to destroy your plant. Ferns are sensitive to insecticides and unlikely to survive even after being treated. Additionally, the disease can quickly spread to your other plants. 

Preventatively treat with an all-natural essential oil spray that contains neem, lemongrass, and lavender to limit any future infestations. 

Always isolate and monitor any new plants for at least a week before adding them to your plant collection. 

Fertile Leaves 

Brown spots on the underside of fern leaves are commonly mistaken for pest infestations but are more likely to be fruiting bodies that are perfectly natural in the fern’s unique multi-stage reproductive life cycle. 

Fruiting bodies pose no harm to the fern, but several human health studies have shown that those with known allergy problems have a 60 – 70% chance of developing allergy-like symptoms to the spores of fern plants, particularly bracken ferns, Pteridium aquilinum

Side effects include skin rashes and respiratory issues often caused within a horticultural setting or large forest stands. For household ferns, simply cut off the sporing leaves and discard them in the trash if you are concerned. 

For more plant articles related to brown leaves, click this link to find out why ZZ plant leaves turn brown.

FAQ Why Are My Fern Leaves Turning Brown

Should I remove the brown leaves on my fern plants?

Yes, periodically pruning the dead leaves from your ferns will help them maintain a healthy and beautiful appearance. Pruning brown leaves also helps prevent pest infestations. 

Citations

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Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.