Why is my Boston fern turning brown? 5 common causes you need to know about

'Why is my Boston fern turning brown?' is a question that many houseplant lovers growing these beautiful evergreen plants end up asking themselves at some point. 

While the Boston fern is a great choice as a houseplant thanks to its suitability for lower-light locations, it does have a set of requirements that need to be met for the plant to thrive. Get these wrong, and you could soon find that the leaves start turning an unattractive shade of brown. 

To help ensure the fronds of your plant retain their vibrant green color, our houseplant experts have identified the common reasons your plant could be turning brown. 

5 reasons your Boston fern is turning brown

Here are the main issues that cause the leaves on your Boston fern to turn brown, and the best remedies.

1. Over or underwatering

Like many other indoor plants, Boston ferns are sensitive to incorrect watering. Get the amount and frequency of your watering wrong and the leaves can start to turn brown. 

It's worth remembering that ferns in nature thrive in humid climates, preferring to grow in moist woodlands. If in doubt, it's best to overwater a little than underwater. 

Tatyana Zhuk, plant expert at the NatureID app, recommends giving your Boston fern 'a drink once every 3-4 days, letting the topsoil dry out by around 0.5in (1-2cm). Check the soil moisture level with your finger or a wooden stick. When watering, pour water all over the soil surface. You can also moisten the leaves.'

2. Insufficient humidity

A related issue that will cause your Boston fern to go brown is insufficient humidity. Tatyana Zhuk says that 'the optimal humidity for your fern is about 50-60%. Mist it regularly when the weather is dry. 

'Use a fine mist sprayer to create a “fog” around the plant and evenly moisturize its foliage.' 

If you think you'll forget to mist, you can get a plant humidifier on Amazon and keep it in the room where you are growing your fern. 

Boston ferns are great as a bathroom plant as they will love the humidity, providing your bathroom has a source of natural light. 

3. You are using hard water for watering

Hard water is generally not suitable for plants growing in your indoor garden, as they evolved to be compatible with rain water. 

Tatyana Zhuk recommends using 'only soft (rain, filtered, or settled for 1-2 days) water for watering. Excess salts are harmful to your plant.' 

Generally, if your plant is suffering from the effects of hard water, you will see leaves that are brown and curling.  

If you can't collect rainwater, simply add some tap water to a bowl or container and leave it to settle for a couple of days before using it to water your plants.

4. The soil in the plant pot is compacted

While the Boston fern likes humidity and plenty of water, it will begin to fail if the soil in its pot is compacted. Compacted soil leads to a lack of oxygen, waterlogging, and root rot. 

In nature, Boston ferns thrive in loamy soils or ones with a high peat content. While peat is not a sustainable potting material, you can add perlite or coir to your potting mix to open up the soil a little. This will allow the soil to breathe and your fern to thrive. 

And if your Boston fern outgrows its pot, repotting the plant will give it the space it needs to grow and thrive. 

5. Too much sunlight

Boston ferns prefer indirect light or even semi-shade, but never direct sunlight. Some dappled morning light is ok, but avoid placing your plant in a location where it will get full lunchtime or afternoon sun. 

Brody Hall, Certified Horticulturist and Co-Founder at The Indoor Nursery, recommends ensuring that your Boston fern 'is not in direct sunlight, which can dry up the soil too quickly and burn the plant’s leaves.' If you like keeping your fern in the window, adding a curtain or a blind can help protect it from harsh lunchtime sun and stop the leaves turning brown. 

As a rule, though, it's best to keep your Boston fern is a room that doesn't get too much direct sun. Boston ferns are therefore a good choice for a bedroom plant in a north-facing room, humid bathrooms with windows, or bookshelf locations away from sunny windows.