Spot a fern when you’re at the nursery or home and garden center, and you’ll likely soon find yourself picturing the perfect place to put the plant in your indoor garden. With their gorgeous, often lacy or ruffled fronds and wide range of soothing greens, ferns make a lovely addition to the indoor garden.
According to Mobee Weinstein, author of The Complete Book of Ferns, growers are constantly expanding their offerings when it comes to ferns that thrive indoors. The book has an extensive chapter on growing ferns as houseplants, and an encyclopedia of ferns.
As Weinstein suggests, and I highly agree, it’s best before you bring a fern into your indoor environment to check out its natural habitat for clues as to if the plant will thrive in your indoor garden and what to do to help it grow well.
Here are the top requirements for growing ferns indoors.
Lighting for Fern Houseplants
Ferns usually require medium light or bright, indirect light. Avoid growing indoor ferns in direct, hot sun. Weinstein suggests an eastern exposure, which I’ve found is ideal. Avoid western exposures, as that is generally too hot. Southern exposures can work, providing the area doesn’t get too bright.
If you have a room that faces a mixed exposure—for instance, I have a room that sits on a northwest corner—that may work. I happen to find that my ferns do well in that room. A full northern exposure room would not have enough light, however.
When you don’t have the right lighting in your indoor garden, you can simply add full-spectrum lighting, which simulates daylight, and your ferns will be happy. You can find fixtures in full-spectrum lighting, as well as bulbs to add to existing fixtures.
Ideal Temperatures for Indoor Fern Growing
Most ferns you’ll find for indoor growing will thrive in temperatures ranging from 70 to 80 degrees, with the ability to withstand some time in higher and lower temperatures. If your home is generally much lower or higher than this range, you may have difficulty keeping ferns happy in your indoor garden.
Ferns also prefer a drop in temperature of 5 to 10 degrees F. at night. If you’re growing ferns on a windowsill, make sure that they don’t get too cold during the winter months or too hot during the peak of summer.
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Potting Soil for Indoor Ferns
Ferns tend to have shallow, thin root systems, according to Weinstein. That means they require a well-aerated, well-draining potting mix. However, you don’t want the mix to drain too quickly, as ferns do need a constant source of moisture and nutrients. Most ferns also do best in a slightly acidic mix ranging between 6 and 7.
If your fern begins to show signs of leaf yellowing and loss and fronds fail to mature to full size, your pH may be off. After checking that your plant has the right lighting and watering regimen and enough humidity, suspect and correct a pH problem. Check out our video playlist on fixing houseplant soil pH here.
Choose a soilless mix for your ferns. Such potting soils contain peat moss as a base and perlite or pumice for drainage. Or, a renewable, more sustainable source of a potting soil base becoming more readily available is coir, which is made from coconut husks.
Watering Your Indoor Fern
Most ferns for indoor growing come from tropical climates and therefore require the soil to be kept evenly moist. There are some ferns that require drier soil, so it helps to know what your fern requires.
Water your fern with warm to tepid water. Water from the tap that is cold can shock the roots of the fern and cause poor or stunted growth and root dieback. If possible, use rainwater on your ferns. Ferns don’t respond well to fluoride and chlorine often found in tap water. Chlorine will dissipate if you let the water sit for 24 hours, but fluoride won’t leave the water.
Water your fern by soaking the pot over a sink or outdoors in the shade, or do bottom watering by sinking the fern into a container that is slightly bigger than the pot the fern is in. See our video on bottom watering here.
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Humidity for Fern Houseplants
Most of the ferns grown indoors are from tropical climates that have 70 to 100 percent humidity. Most homes range from 40 to 60 percent humidity. That means that ferns require additional humidity to do well in your home. If you are doing everything else right and find that your fern’s leaf tips are drying and the fronds are drying out, you may have a humidity problem.
Test the humidity in the air surrounding your fern with a hygrometer. This useful device will tell you the relative humidity and temperature. The relative humidity refers to the percentage of moisture in the air sampled at a specific location, taking into consideration the total amount of moisture that particular air can hold without the vapor being precipitated into rain or fog.
So, a reading of 50 percent humidity indicates that the air sample contains half of the moisture it can hold before the moisture condenses and becomes visible. Air temperature affects relative humidity. Warm air contains more humidity than cooler air.
To increase humidity for your ferns, use a humidity tray, as well as group your plants. Plants humidify each other. So, the more plants you have, the more humid the air will be. You can also mist your ferns, but keep in mind that the effects are short-lived. Misting will have to be repeated several times a day to make a difference. If you live in a particularly dry climate and want to grow ferns, you may have to use a humidifier.
Common Pests on Indoor Ferns
Scale and mealybugs are common on indoor grown ferns. These pests suck on fern sap and can weaken and even kill ferns. Their sucking creates a sticky substance on surrounding furniture and the floor and will cause yellowing fronds. Treat both pests by spraying outdoors with horticultural oil, which will suffocate them. Mealybugs can also be sprayed with isopropyl alcohol.