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Growing tropical ferns indoors

Deborah Brown

illustration of a Boston fern

Nephrolepis exaltata 'Bostoniensis'
Boston fern

Light levels
Most ferns thrive in filtered light or shady sites outdoors, but the tropical ferns we use as houseplants are poor candidates for low-light locations. Golden pothos (Epipremnum aureum), heart-leaf philodendron (Philodendron scandens oxycardium), snake plant (Sansevieria trifasciata), and Chinese evergreen (Aglaonema commutatum) are much better candidates for locations near north windows or other poorly lit places in your home.

Tropical ferns actually grow best indoors in "medium" light such as what you'd find in an east-facing window or a few feet from a west or south-facing window.

During our short days from November through February, ferns can be placed directly in a west or south window with no ill effects. But as days lengthen and sunlight becomes more intense, you run the risk of burning delicate foliage in such bright places, unless the light in those windows is filtered by large trees nearby, or by sheer shades or curtains, inside.

Without adequate light, no fern will prosper indoors, but there's more to growing ferns than providing enough light.

You'll find that new ferns come with care tags suggesting they need to be kept evenly moist. That means the soil should never be allowed to get very dry; it doesn't mean it should always stay wet.

It's important to water ferns thoroughly whenever you water. Don't just dribble a little water on top of the soil from time to time. Use room temperature or lukewarm water; cold water can damage tropical roots. If at all possible, avoid using softened water. Its repeated use will result in an accumulation of salts in the soil, which eventually injures the plant's roots.

Water until excess moisture begins to drip through the container's drain holes, then spill out whatever remains in the tray or saucer after a few minutes. Wait to water again until the soil surface begins to feel dry to the touch. It's a mistake to water before that; soggy soil encourages root rots.

Ferns are usually potted in highly organic soil that's porous, yet moisture-retentive. When it's time to transplant them into larger containers, choose potting soil that contains a large percentage of peat moss.

Air circulation
Place ferns far enough from walls and other plants to insure good air circulation. Ferns look particularly handsome displayed on pedestals or in wicker ferneries. They're also commonly grown in hanging baskets, but you must be careful not to display them too near the ceiling. The higher they are, the hotter and drier the air, especially during the heating season. This may cause the tips of your fern's fronds to turn brown and die.

Ferns are known for their high humidity needs. Some people still mist their ferns to increase humidity, but it's not very effective. Unfortunately, misting also increases the likelihood of foliar leaf spot diseases; it's better to rely on room humidifiers.

Because it's difficult to improve humidity significantly indoors, it's usually better to concentrate on proper watering to eliminate moisture stress.

Typically ferns have modest fertilizer needs; they can be damaged more easily than most houseplants if you overdo it. Over-fertilizing will result in browning and drying that begins at the tips, then works its way back into the rest of the fronds. A lack of nutrients results in foliage that pales and loses its vibrant green color.

Fish emulsion seems to work well, though other fertilizers meant specially for houseplants are fine, too, provided they're mixed ½-strength and applied sparingly. Fertilize only when the plants are actively putting on new growth, or if the foliage appears a paler green than normal.

Keep them clean
It's important to keep fern foliage clean. Dusty leaves may provide a haven for mites or insects. The dust also filters sunlight so less reaches the foliage. You can wash ferns with a gentle spray of lukewarm water from the sink, or swish them upside-down in a sink or laundry tub of lukewarm water to which you've added a few drops of mild dishwashing liquid.

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