11 Common Causes of Boston Fern Fronds Turning Yellow

When healthy and vibrant, I think my Boston fern (Nephrolepis exaltata) makes a big statement. I love that their large fronds cascade out in all directions, creating a dramatic display of green. However, sometimes these stunning ferns develop one yellow frond, then another, and soon the whole plant looks sad. In my experience, many different factors can lead to yellowing Boston fern leaves, including environmental issues and pests. Read on to learn about the most common causes of Boston Fern fronds turning yellow, plus, I’ll share what I do to remedy the issue at home.

11 Common Causes of Boston Fern Fronds Turning Yellow

11 Common Causes of Boston Fern Fronds Turning Yellow

1. Overwatering

A cluster of boston fern fronds with some turning a pale yellow

If you are watering your plant, so the soil is constantly wet, you are likely overwatering. While Boston ferns like slightly moist soil, the soil should not be saturated.

When the soil is always damp, the plant’s roots may have difficulty taking up water and nutrients. Damp soil may also lead to a fungal infection known as root rot.

Remember that low temperatures, low light, and high humidity will all decrease the frequency you’ll need to water.

For more, see our in-depth guide to when and how to water Boston Ferns.

2. Underwatering

Underwatering may also lead to yellow leaves. If your plant does not have access to enough moisture, it will have difficulty completing crucial processes. This can lead to yellowing leaves over time.

It’s best to water your Boston fern when the top two inches of soil is dry. Check the soil at least once a week and water when dry.

It’s also important to remember that you will need to water more often when the temperature is high and/or humidity is low. 

3. Improper Soil Type

A person repotting a boston fern plant

Soil type also plays a significant role in soil moisture. Soils that contain lots of organic matter and/or clay hold onto water for a long time. However, materials like perlite, pine bark, and sand can all increase drainage.

Boston ferns prefer well-draining soil. If the soil doesn’t have proper drainage, the plants may sit in constantly moist soil. This can lead to problems with water and nutrient uptake and therefore cause yellow leaves.

Choose a potting soil that contains organic material to hold moisture as well as materials to increase drainage. If you think your fern is in the wrong type of soil, repot your Boston Fern into a better soil mix.

4. Low Humidity

Like many houseplants, Boston ferns prefer high humidity. If your house is extremely dry or even at average humidity, your plant may suffer.

Many homes have humidity levels below 50%, especially if heat or air conditioning is running. While an indoor humidity of 30-50% is a good range for human health, it is often too low for Boston ferns.

Dry air can lead to increased rates of transpiration. This means that plants are losing moisture more quickly through their leaves. This can lead to low water content in the plant, which can sometimes cause yellow leaves.

To increase the humidity around your plant, you can use a humidifier. You can also mist the air around your plant, but this solution isn’t as effective.

5. Nutrient Deficiency

A person placing a handful of fertilizer around the soil of a plant pot

Boston ferns, like other plants, need a range of nutrients to thrive. While young plants can survive without fertilizer for a bit, plants will eventually need an input of nutrients.

Fertilizing Boston fern plants is the best way to provide your plant with the nutrients it needs. Apply a low-dose fertilizer about once a month in the spring and summer. Choose a product that is designed for vegetative houseplants to provide the correct amount of nutrients.

6. Sap-Sucking Pests

Numerous small pests seek out Boston ferns to suck the plants’ juices. These include spider mites, thrips, and aphids.

While these are all unique species, they cause similar harm. First, the pests use their piercing mouthparts to cut through the top layer of the fern’s fronds. Then, they suck out the plant’s sap.

A few pests won’t cause much damage and may even go unnoticed. However, since these pests can rapidly multiply, they can quickly reach large numbers.

As a collective, the pests can remove a large amount of sap. This can eventually lead to small discolored spots—an effect known as stippling. Over time, this may transform into yellow leaves.

Fortunately, it’s easy to determine if these pests cause yellow leaves. If you see them, they’re likely the cause! But if you don’t see any pests or only a few, something else is likely to blame.

7. Cold Temperatures

A boston fern plant being grown outside against a blue sky

Another possible cause of yellow leaves is low temperatures. Despite its common name, the Boston fern is native to tropical regions, including Florida, Central America, and the West Indies. As such, it prefers warm temperatures.

If air temperatures remain below 60ºF for an extended time, your plant may develop yellow leaves. Short periods below 50ºF can also cause tissue to die, resulting in discolored leaves.

Along with cold temperatures, large swings in temperature can also lead to yellowing leaves. This may occur if your plant is located in a drafty area or if you move your Boston Fern from a warm location to a cooler location.

Any temperature change can stress your plant, which may cause yellow leaves. Therefore, keep your plant out of drafty areas and slowly acclimate it to new areas.

For more, see our in-depth guide to Boston Fern temperature tolerances.

8. Exposure to Direct Light

Like most types of indoor ferns, intense, direct light can damage a Boston fern’s leaves and lead to yellowing. This is especially true if the plant was in a darker area and then suddenly exposed to direct light.

Aim to keep your plant in an area with bright yet indirect light. And if you are moving your plant to a sunnier location, do so gradually. For example, give the plant a few hours of bright light to start, then a few more hours the following week.

9. Not Enough Light

A boston fern growing in partial shade

Indeed, Boston ferns don’t need (or like) direct light. That said, they require lots of bright, indirect light to thrive.

If your plant is in a dark area, it may not be getting the light it needs to photosynthesize properly. This means the plant will be unable to produce the energy it needs. One sign of this could be yellowing leaves.

10. Plant Age

Just like humans and other living organisms, Boston ferns age over time. Part of the aging process involves the dying of older tissues.

If your Boston fern is old, you may notice older leaves becoming discolored and then dying. As long as the other leaves remain healthy, this is typically not cause for concern.

11. Over Fertilizing

A boston fern planted in a wooden planter

While Boston ferns need nutrients to thrive, they can also be harmed by too many nutrients. Many nutrients exist in salt form. Therefore, applying fertilizer adds salts to your plant.

If you apply too much fertilizer or too strong a dose, your plant may develop issues with high salt levels. This can stress out the plant and result in the older leaves turning yellow.

If you think you have applied too much fertilizer, you can water your plant well. This will help flush out the excess salts.

How to Fix Yellow or Brown Leaves on a Boston Fern

A close shot of vibrant green boston fern fronds

The first step to fixing discolored Boston fern leaves and brown tips is identifying the cause. Look through the list above and see what factor(s) are likely to apply to your situation.

Next, aim to fix that specific factor. For example, if the soil seems constantly moist, decrease the amount you water and check that your pot has drainage holes. 

If you’re unsure of the cause, you can look at the conditions your fern is in and check if it matches up with the ideal environment.

Light:bright yet indirect light
Water:water when the top two inches of soil is dry; soil should remain slightly moist
Soil:well-draining with a pH between 5.5 and 6.5
Fertilizer:fertilize once a month in the spring and summer
Humidity:moderate to high; above 50%

Yellowing or Brown Boston Fern Fronds FAQs:

How do you fix yellow leaves on a Boston Fern?

This depends on the cause of yellow leaves. Ensuring that you are providing the proper environment is a good first step.

Can yellow Boston Fern leaves turn green again? 

Once leaves turn yellow, they are unlikely to turn green again. However, new leaves can emerge, and your plant can return to good health.

Can direct sunlight cause Boston Ferns leaves to turn yellow? 

Yes, direct light can cause Boston fern leaves to turn yellow.

Does the type of water cause Boston Fern leaves to turn yellow? 

Boston ferns can be sensitive to hard water as well as chemicals in tap water. While these may cause yellowing, they aren’t the most likely cause.

Can over-fertilizing cause Boston Fern leaves to turn yellow?

Yes, over-fertilizing can cause Boston ferns to turn yellow. A dose of fertilizer that is too high can cause high salt levels, which leads to plant stress. This will result in older leaves turning yellow first.

The Final Word

Now that you know the many potential causes of yellow Boston fern leaves, it’s time to get to work discovering which one applies to your plant. By fixing the cause of yellowing leaves, you can help your plant return to a healthy state.

For more, see our in-depth guide to the meaning and symbolism of ferns.

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