Ferns are often planted in shady areas to provide bright, refreshing greenery, but some ferns need sunny gardens. Certain fern species need a lot of water, thriving in damp locations, and others do best with a little less moisture. Selecting the right ferns for your garden is important. If you have time to water plants several times each week, then moisture-loving ferns are fine choices. If you just do not have time to water or simply forget to check on your plants, then go for ferns that can handle a little neglect.
Fern Hardiness and Cultural Requirements
Ferns are generally hardy in U.S. Department of Agriculture plant hardiness zones 2 through 11, depending on their variety. Some ferns, such as northern maidenhair or five-finger fern (Adiantum pedatum), thrive in environments that have cold winters; northern maidenhair, which needs fast-draining soil, is hardy in USDA zones 2 through 8. Other ferns, including Boston or sword fern (Nephrolepis exaltata, USDA zones 9 through 11), require milder environments. Boston fern grows best in moist soil and high humidity but tolerates drought; it requires partial to full shade when planted outdoors. Royal fern (Osmunda regalis, USDA zones 3 through 9) thrives in wet, organically rich soil and four to six hours of direct sunlight each day.
Water Requirements
Ferns growing in the ground outdoors need about 1 inch or 3 gallons of water each week. The amount should be adjusted for the growing conditions, the fern species' requirements and the weather. All newly planted ferns should be watered as often as necessary to maintain uniformly moist soil for the first one or two months, until they are well-established. Afterward, the top 1 inch of soil can be allowed to dry between irrigation sessions for ferns such as the northern maidenhair. The soil for varieties such as Boston and royal ferns should always be slightly moist.
Ferns in fast-draining soil have to be watered more often than those planted in slower-draining soil. All ferns have to be watered more than normal during hot summer weather. If it does not rain, give each fern 3 gallons of water, and then check the soil every few days. When the soil begins to get a little dry, give each plant another 3 gallons. A gray tint to ferns' leaflets is an indication that the plants are not getting enough water. A 2- to 3-inch depth of organic mulch spread over the soil surface around the ferns -- but not touching the plants -- helps to conserve moisture.
Fertilizer Requirements
Do not give ferns a lot of fertilizer. They are very sensitive to it and end up with burned roots and brown, crispy or crinkled leaflets when given too much. A balanced, 14-14-14, slow-release, granular fertilizer is all ferns planted in the ground outdoors need. A common application rate for ferns is 1/4 cup per 20 square feet, but the amount varies among fertilizer products; follow the manufacturer’s recommendations on your fertilizer's label. Give them one application of the fertilizer in spring when they begin to grow new fronds and leaflets.
Sprinkle the fertilizer evenly on the soil surface beneath the fern stems, or fronds, to a few inches beyond their outer edges. Mix the fertilizer into the top 1/2 inch of soil lightly with a hand rake, being careful not to disturb roots. If fertilizer gets on the fern fronds, brush it off gently by hand or with a broom.
Fern Diseases
Ferns are susceptible to a few diseases, including bacterial blight, Pythium root rot and Rhizoctonia blight. Bacterial blight causes translucent spots on the leaflets; the spots get bigger and change to reddish brown with purple edges. Water ferns from below their stems with a soaker hose or watering can to avoid wetting the leaves to help prevent that disease. Prune infected fronds and clean up debris from around the ferns to help prevent the spread of the bacteria. Disinfect the pruners with a household disinfectant before beginning and between cuts. Rinse off the disinfectant with clean water, and dry the pruners before using them. Throw the diseased fronds and debris in the trash; do not put them in a compost pile. A fresh layer of mulch will cover the bacteria below and help prevent its spread.
Pythium root rot causes fern roots to rot and fronds to turn gray or yellow and wilt. Rhizoctonia blight causes brown spots on fern leaflets and a fungal webbing between the fronds. Treat ferns infected with either of those diseases, as well as ferns infected with lesion nematodes, by applying a fungicide that contains thiophanate methyl; spray it on the fronds, and drench the soil with it. That fungicide is available in a variety of formulas. A 40-percent wettable powder that is 25 percent thiophanate methyl is commonly diluted at a rate of ¾ to 1 ½ ounces per 12 ½ gallons of water to drench 50 square feet of soil. Follow the fungicide manufacturer’s recommendations carefully. Wear eye-wear and protective clothing to cover all of your skin when handling, mixing and using a fungicide.
Fern Pests
Ferns are not attacked by many pests, but mealybugs, scales and nematodes can become a problem. Mealybugs are small, oval, white to off-white, mealy-looking pests. Scale insects are small, round or oval, flat and usually tan. Both mealybugs and scale insects suck juices from fern leaflets. They usually can be found on the undersides of leaflets but may be on the plants' tops and stems, too. Don't confuse these insects with ferns' reproductive spores. Many kinds of ferns develop reproductive spores on their leaf undersides; the spores are spaced evenly, but scale insects and mealybugs tend to be in groups.
A strong spray of water from a garden hose usually gets mealybugs off ferns. Spray water on the undersides of leaves and stems as well as other plant parts. Spray the ferns in the morning every few days until the mealybugs are gone. Both mealybugs and scale insects can be wiped off with a cotton ball or swab that was dipped in isopropyl rubbing alcohol. The pests also can be scraped off with a thumbnail or old toothbrush. Pesticides are not a suitable option to use because they can damage ferns.
Foliar nematodes cause little, dark-green dots toward the bottom of fern stems, and the dots get bigger and turn black or brown. Ferns cannot be saved from foliar nematodes. Dig up the affected ferns, and throw them in the trash. Do not add them to a compost pile. Lesion nematodes attack fern roots, causing the stems to turn gray and wilt before they die. Treat ferns with lesion nematodes in the same way as ferns with Pythium root rot.
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