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Why Is My Boston Fern Turning Black? (9 Causes+How To Fix)

Boston ferns are popular houseplants that can brighten up any room with their evergreen fronds. No wonder it is heartbreaking to see your Boston ferns turn black. But why is the Boston fern turning black? How can you fix it? Let’s find out.

It is natural for the old fronds of Boston fern to turn black, but if the younger leaves start turning black, it signifies a problem. Fungal diseases like root rot are the primary causes of black leaves. You will need to eliminate the decaying roots and repot the plant to fix the problem.

I will discuss the reasons that cause black fronds in Boston ferns in this article. I will also provide you with information about how to fix the problems and save your Boston fern. So, keep reading.


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What causes my Boston fern to turn black?

Boston ferns are low maintenance and easy to grow plants, but it doesn’t mean you will not care about their basic requirements.

Black leaves are not caused in one or two days, and the plant will show other signs of stress before turning black.

Keeping the ferns in unhealthy conditions for a prolonged period will make the fronds go black.

Many reasons can be responsible for black fronds in Boston ferns.

Let’s understand all the possible reasons.

Improper watering

Boston fern moisture meter

Improper watering will cause the fronds of your Boston ferns to turn black.

Both overwatering and underwatering can cause this issue. 

When you overwater your plant, its roots will start to rot, causing the tips of the fronds to turn black.

Whenever root rot takes place, the roots turn fragile and fail to perform their basic function of carrying water and nutrients to the plant.

The plant undergoes nutrition deficiency and fails to perform its basic life processes, due to which its fronds start to turn black.

If not treated within time, your Boston fern can even die.

Boston ferns can turn black at the edges if you are underwatering the soil.

They prefer their roots to be evenly and consistently moist. 

In their natural habitat, they grow in soil that retains moisture and has a porous structure that drains out the excess water from the soil.

So if you underwater the plant, the soil will dry out quickly, causing the leaves to turn crispy, brown, or black At the edges.

Low humidity

Boston fern high temperature

One of the major reasons for black fronds in Boston ferns is low humidity. 

Boston ferns are tropical plants adapted to live in regions where humidity levels are as high as 80%.

Hence, they cannot withstand dry air for a longer period as it will increase the transpiration rate, resulting in excess water loss from the leaves.

The plant will dehydrate, leading to shriveled and black leaves.

Usually, when grown as houseplants, the humidity in the indoor environment is too low, which is inappropriate for fern growth, leading to black, dried, and crispy leaves.

In the indoor environment, they will face humidity constraints from the following:

  • Air conditioners: The air coming from ACs creates unsuitable air currents and dries up the air, causing the plant to dehydrate and turn black.
  • Forced air: Like ACs, forced air forms dry air currents that lower the humidity level and raised the temperature. The high temperature will cause the soil to dry out quickly, lowering the humidity around Boston ferns.
  • Heating sources: Any heating sources like fireplaces, chimneys, and heaters can create conventional heat currents inside the house, which causes dry air to flow around the plant.

Light issues

Boston fern in low light

Boston ferns will grow well when they receive bright, indirect sunlight.

They grow under the canopy of trees in their natural habitat, which filters the light.

Direct sunlight will cause them sunburn.

If they are placed in a location with too much sunlight, their leaves will start to lose water quicker.

This will cause the soil to dry out quickly, leaving the fronds to turn black and crispy with a dying appearance.

On the hand, the plant can also turn black if it doesn’t receive light.

They will need light for carrying out photosynthesis to prepare food and get energy. 

Without light, the leaves will not get the energy to maintain their green color.

The leaves will first turn yellow, then brown and black ultimately.


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Temperature stress

Boston fern prefers optimum temperatures of 60-75ºF.

A sudden temperature rise can cause the plant to lose excess moisture from its leaves, causing stress.

The high temperature will also increase the rate of evaporation from the soil.

The leaves will shrivel and turn brown initially, but continuous moisture loss will lead to black leaves. 

Also, Boston ferns can’t tolerate extremely cold weather, and their leaves will turn black if you expose them to a temperature below 50ºF.

The root system stops functioning, and the plant’s metabolism deteriorates due to cold, causing the leaves to wilt and turn black.

Sudden temperature fluctuation can often cause the plant to turn black.

This happens when you move the plant from one place to another place.

A change in environment can stress the plant, due to which its leaves can turn brown or black.

Pests

Pest will cause the leaves of the Boston fern to turn black.

Some common pests that you might notice on Boston fern include mealybugs, caterpillars, spider mites, scales, and thrips. 

These pests are too tiny to catch our attention, so they are often unnoticed.

The bugs suck out the sap from the leaves making the plant lose its nutrients and water.

In addition, the pests damage the roots system and attract diseases to the plant, due to which the leaves of your Boston fern turn black.

Overfertilization

Fertilizing indoor plant

Overfertilization is one reason that will cause discoloration of leaves. 

Many plant owners do the mistake of feeding the plant more than required, thinking that fertilizing more will increase the growth of their plant.

However, it doesn’t happen, and eventually, the plant develops different problems.

Too much fertilizer will lead to salt build in the soil that can burn the plant’s root system and make the tips of the fronds black.

Overfertilization mainly occurs during the winter season as the plant remains dormant and does not need fertilizer for new growth.

Nematodes

Nematodes are thread-like roundworms with soft bodies that live inside the soil surface.

They usually attack the plant’s root system and reduce its ability to pull water and nutrients from the soil.

Bud and stem nematodes distort and kill buds and leaf tissues which causes stress and disturbs the normal functioning of the plant leading to black leaves.

If you notice a brown, black spot or strips on the upper side of the leaves, then there may be nematodes present in the soil.

Bacterial soft rot

Bacterial soft rot is a disease caused by several bacteria, most commonly Pectobacterium and carotovorum.

The sign of this disease includes small soft to black spots with an unpleasant smell from the plant. 

They enlarge over time and become soft and sunken.

They destroy pectate molecules in plants that bind cells together, due to which the plant structure falls apart, leading to black leaves.

This disease can enter the plant through contaminated tools, insects, or infested plant debris or soil. 

Natural black fronds

There is one situation where Boston fern with black fronds is considered natural.

You may find tiny black spots on the underside of Boston fern leaves arranged in regular rows. 

These black spots are the spores used for the propagation of Boston ferns.

Eventually, the spores will fall off the leaves and grow back into reproductive structures.

Do not worry whenever you find these spores, do not worry, as it is a sign of healthy ferns.

Like any other plant, Boston ferns can experience browning as they ages.

When new growth takes place, the old leaves will wither and turn brown to black to clear the way for the new growth. 

This is a natural process.

If you find such discolored leaves, prune them from your plant.

How to fix black fronds in Boston ferns?

If your Boston fern has black fronds, you need to identify the cause quickly and take action without any delay to save your plant’s life.

You can fix black fronds by providing the plant with enough light, adequate fertilizing, proper watering, and the right conditions. 

The fronds that have turned black will not become healthy again, so you need to prune them off your plant.

Since we have already discussed the causes earlier, let us understand how to treat these problems.

Water consistently

Boston fern watering

If you don’t want black leaves, stop overwatering or underwatering your Boston ferns.

You should keep the soil moist but not damp.

  • If, by any chance, you have overwatered your Boston fern, prune the discolored fronds and all other damaged parts with sterilized scissors.
  • Check the roots for root rot. If you find that the roots have turned black and mushy, then prune them, leaving behind the healthy ones.
  • Get a new pot and add a rich, well-draining fresh potting mix and repot your Boston fern in it. Ensure that the pot you are using must have drainage holes to drain the excess water from the soil.
  • After repotting, water the soil thoroughly and keep the plant in bright, indirect light. Avoid over-fertilizing the plant and wait until you notice new growth.
  • Before watering again, check the moisture level of the soil. You can check moisture by inserting your finger into the soil. Water the plant only when the top 1 to 2 inches of the soil feels dry. You can also use a moisture meter.
  • Reduce watering during the winter season since the plant does not actively grow and so it doesn’t need much water.

Also read: How To Water Boston Fern? (How Often, How Much & More)

Fix the humidity

Boston fern humidifier

Boston ferns being tropical plants need high humidity to remain alive. 

There are some ways to increase humidity around the plant:

  • Grouping plants: You can group your Boston fern with other houseplants to increase the humidity around it. As the plants transpire, they will release moisture into the air, adding humidity to the environment.
  • Use humidifiers: You can buy a humidifier to adjust the humidity level as per your plant’s requirements. 
  • Misting: You can mist the leaves of your Boston ferns twice a week to increase the humidity level.
  • Use pebble trays: You can keep your Boston fern on trays filled with water and pebbles. The water from the tray will evaporate and create a moist environment around the plant.

Also read: Should I Mist My Boston Fern? (How Often+Pros & Cons)



Fix the light

Boston ferns can tolerate morning sun for a few hours, but the afternoon sun can be too harsh.

So, to make your Boston fern thrive, select a location that can provide them with bright, indirect light for a minimum of 3-4 hours every day.

Make sure to keep the Boston fern away from direct sunlight.

  • You should keep your Boston fern near a South or West-facing window to provide them with the correct amount of light.
  • You can use curtains to filter the direct light if you have a sunny window. 
  • If you wish to keep your plant outside, choose a shady spot so that it remains protected from direct sunlight. 
  • Rotate the plant once a week so that all of its sides will receive an equal amount of light.
  • If natural light is limited in your house, you can use artificial lights to fulfill Boston fern’s light requirements.

Also read: What Kind Of Lighting Does A Boston Fern Need?

Adjust the temperature

Boston fern prefers to stay in a controlled environment with average room temperatures.

Room temperatures between 60-75ºF are suitable for your plant but make sure that the room doesn’t have air conditioners or heaters.

  • If the temperature level drops, immediately bring your plant to a warm location.
  • Keep the plant away from cold drafts and frosts during the winter months. 
  • And during extremely hot conditions, keep your Boston ferns in a shadier spot away from direct sunlight.
  • Use curtains or keep the plant a few feet away from the window to prevent excess heat. 
  • Do not place your plant near any heating device like radiators, heaters, or furnaces, as the heat waves from such devices can burn your plant’s leaves. 

Also read: Boston Fern Temperature Tolerance: +Ideal Temperature

Treat pest infestations

Boston fern neem oil

There are many ways to treat pest infestation from your Boston ferns.

  • Wash your plant: Rinse your Boston fern by giving it a good wash to eliminate the pests. After washing, keep the plant in indirect sunlight for a few hours to let it dry.
  • Spray solutions: Many remedies are available to treat pests in Boston ferns. You can use Neem oilinsecticidal soaps, dish wash soap, or herbs. Mix any of these with water, prepare the solution and spray it over your plant. Continue to apply the solution for a few weeks until the pest goes away.
  • Use insecticides: If the pests are still present after using homemade remedies, you need to look for insecticides. Some insecticides can be toxic, so do not overuse them. Read the application instructions on the label before applying them to your plant.

Also read: Boston Fern Pests And Diseases: Common Bugs & Diseases+How To Fix

Treat nematodes

To destroy the growth of nematodes, you need to add compost or rotten manure to the soil.

This will encourage the growth of beneficial fungi and bacteria that will fight against nematodes.

You can change the potting mix with organic ingredients if any new infestation develops.

If the infestation is quite bad, you need to discard the soil and the infected plant.

Treat the diseases 

If you have grouped your diseased Boston fern with other houseplants, isolate it to prevent further infestation.

  • Prune off the infected leaves, stems, and roots from the plant with sterilized plants.
  • Treat the disease by applying fungicides to the plant.
  • Make sure that the surrounding region around the plant is well ventilated. 
  • Do not keep the leaves wet and prefer watering the plant in the morning only.

Fertilize adequately

Boston fern fertilizer

 If you have over-fertilized your Boston fern, this is what you need to do:

  • Stop fertilizing the plant for some time if you notice any signs of overfertilization.
  • Prune off the affected leaves and other parts of the plant.
  • If there is a salt build-up due to overfeeding, water the Boston fern thoroughly to leach out the excess salts from the soil.
  • Once your plant has recovered, use a water-soluble liquid fertilizer with an NPK ratio of 20-10-20 and dilute it at half strength to prevent over-fertilization.
  • Fertilize the plant during the growing season and avoid fertilizing during winter.
  • Always water the plant before fertilizing if the fertilizers can evenly spread on the soil.

Also read: Should I Fertilize My Boston Fern? (Ideal Fertilizer+When & How Much)

Final thoughts

Witnessing your Boston fern turn black is unfortunate, but it can happen if you miss the initial signs that the plant gives out. Black leaves or fronds occur over time, indicating that the plant has been facing problems for a while now.

I have discussed all the possible problems that make your Boston fern go black. Unless it is happening due to natural causes like aging, you should observe your plant thoroughly and address the problem as soon as possible.

You must remove the black leaves or fronds from your Boston fern as they will not turn green again.


Reference: University of FloridaThe University of Arkansas DivisionTexas A&M University SystemThe University of GeorgiaUniversity of New HampshireWikipediaThe Royal Horticultural Society.