How to Grow Ferns in Containers

Ferns come from many genera and grow in a variety of climates. Although ferns vary widely, they require similar growing conditions and care when planted in pots: They all need well-drained potting mix, and watering and fertilizer schedules. Also, they are all susceptible to the same pests and diseases.

Check the preferred lighting conditions for your fern species. For example, Boston fern (Nephrolepis exaltata), which is a perennial in U.S. Department of Agriculture plant hardiness zones 8b through 11, does well in indirect sunlight or full shade while maidenhair fern (Adiantum species), perennial in USDA zones 9 through 11, does best in shade. Most houseplant ferns grow well in a north-facing window.

All pots -- including hanging baskets -- used for ferns must have bottom drainage holes. Ferns thrive in evenly moist soil, but their roots rot if their pots do not drain well. Shallow pots work best because ferns do not have deep root systems. Use small pots for small plants, and move up to larger pot sizes as the ferns grow.

When you move a fern into a new pot, the new container should provide 1 inch of growing room all around the root ball. So use a pot 2 inches larger in diameter than the previous pot. Repot a fern when its leaves spill over the edges of its container,but before its roots completely fill the pot.

Fern potting mix must drain well but also hold moisture. Use a commercial fern potting mix or make your own by combining equal portions of coarse sand, peat moss and garden soil. Leaf mold or ground sphagnum moss can be used in place of peat moss. You can also replace part of the coarse sand with charcoal chips. Before using the potting mix, sterilize it in a closed pan in a 200-degrees Fahrenheit oven for 20 to 25 minutes. Doing so kills disease-causing organisms in the soil.

Most ferns need water often enough to keep their soil moist but not soggy. The amount of water ferns need depends on the time of year, growing location and species. Boston ferns, for example, grow best when the top of their soil is allowed to dry between waterings. Maidenhair fern's soil should be constantly moist.

Keep a close eye on the plants to ensure they get enough water. Either overwatering or underwatering can result in yellowed or wilting leaves, brown leaf tips, loss of foliage and slow growth. If too much water is the problem, the soil is wet and heavy, and the roots start to rot. If too little water is the problem, the soil looks dry, and the pot feel lightweight.

Most ferns in pots need fertilizer once each month while actively growing, spring through fall. Potted ferns indoors can be fertilized every other month during winter as well. Use an all-purpose houseplant fertilizer when feeding potted ferns. If, for example, you use a water-soluble, 24-8-16, all-purpose plant food, then mix 1/2 teaspoon of it with 1 gallon of water, and apply the mixture to the fern's soil as a regular watering. Unless the label describes the product as a foliage fertilizer, avoid getting the fertilizer or fertilizer-water mixture on the ferns' leaves.

Trim ferns periodically to remove dead foliage. How often you prune will depend on how fast the plants grow and when old fronds die. Disinfect tools before pruning and between pruning multiple plants to avoid introducing diseases. Soak pruning tools in a solution that is 1 part bleach to 3 parts water for at least five minutes. Then rinse them with clean water before use.

Healthy ferns rarely suffer from pest problems. If pests show up, however, they are usually scale insects or mealy bugs. Both are very small; fern scales are 5/100 to 9/100 inch long. Scales are hard-bodied insects with no legs that can be seen, and mealy bugs are soft-bodied with a white or gray coating. Ferns are sensitive to pesticides, but you can use horticultural oil or insecticidal soap to their infestation of scales or mealy bugs. Most concentrated horticultural oils and insecticidal soaps are applied by mixing 2 to 5 tablespoons of the product with 1 gallon of water. Spray enough of the product-water mixture to cover the top and undersides of fern leaves and stems. Read and follow label instructions for the specific product you use, however.

Ferns occasionally develop diseases. Avoid problems by using sterile potting mix and keeping the potting soil evenly moist rather than soggy. Many problems can be corrected by proper care while others are lethal.

Drought and overfertilization cause leaf browning. Treat by watering ferns thoroughly and reducing fertilizer amounts.

Bacteria blight (Pseudomonas cichorii or Pseudomonas gladioli) results in translucent leaf spots that turn reddish brown. Discard infected plants.

Foliar nematodes (Aphelenchoides fragariae) show up as small, green spots on bases of fronds, which turn black as they grow. Discard infected plants.

Nematodes (Pratylenchus species) make foliage wilt and roots rot. Discard infected plants.

Use caution when working with horticultural oil, insecticidal soap or a different treatment. Wear waterproof gloves, a face mask or, if required, respirator, as well as goggles, waterproof closed-toe shoes, a long-sleeved shirt, long pants and a hat to keep chemicals off your skin. Mix and spray the product in a well-ventilated area, preferably outside on a windless day. Wash your clothing and hands thoroughly after using chemicals, following label directions for cleanup.