Ferns include nearly 12,000 species within a unique category of plants that do not reproduce by seeds produced by flowers that pollinate (sexual reproduction), as do virtually all other plant species. Instead, ferns propagate via spores, which are reproductive units that look like small dots on the undersides of the fronds. Fern plants can drop millions of spores onto the ground, but only a few will find ideal conditions will grow. Ferns have been in existence for more than 300 million years, and are easily recognizable because of their lace-like leaves, known as fronds.
There are so many different species of fern that each must be approached individually to fully understand its characteristics and cultural needs. Some are giant tree-like plants, while others rarely grow above 1 inch in height. Most like shady conditions, but a few grow best in nearly full sun. Some like dry soil, while most need to be kept constantly moist. However, there are some common things to know if you want to grow ferns in your garden or home.
How to Grow Ferns
Most of the popular varieties of ferns for the garden should be planted in a part-shade location, in soil that is rich and which is both moist and well-drained. Spacing should depend on the type of fern—some are mat-forming, and will quickly spread to blanket an area, while others are self-contained and can be used as specimen plants among mixed plantings.
The only rule of thumb for growing ferns is to keep them moist—most varieties, that is. Many ferns are so easy to grow that they can become a nuisance, spreading where you don't want them unless you supervise them. Watch for slug damage through the season. Fronds can be left in place to protect the crowns over winter but should be cleaned away in the spring.
Most ferns prefer a shady location, but they don't do well in deep shade. The dabbled shade provided by tree branches provide the best conditions. Think about how they grow in the forest and try and find similar conditions in your yard.
Ferns can handle some direct sunlight, however, the more sun they get, the more moisture they will need. Only a few fern species, such as ostrich fern (Matteucia struthiopteris) will tolerate dry, hot, sunny locations.
Nearly all ferns prefer a soil that is moist and well-draining. Most do best in slightly acidic to neutral soil, from 4.0 to 7.0 in pH, but some, such as the maidenhair fern (Adiantum), requires a more alkaline soil.
Water ferns regularly during periods without rain, and do not let the soil get totally dry. A 2-inch-thick layer of mulch will help keep the roots cool and damp. When grown indoors, water the plant slightly every day.
Temperature and Humidity
Most (not all) ferns like a humid environment, but their temperature tolerance is quite broad. There is a fern for almost every climate, provided soil and humidity needs are met.
Although not essential, you can use a slow-release fertilizer mixed into the soil in early spring. Ferns are sensitive to fertilizer, so don't overfeed.
Potting and Repotting
When using ferns as houseplants, choose tropical species. Rather than standard potting soil, ferns will grow best in a richer medium, such as a fern-specific commercial mix or compost mixed with peat moss and sand. Repotting is necessary when the plant begins to crowd its container, which may lead to smaller fronds.
Propagating Ferns From Spores
To collect fern spores, wait until they darken and start to fall off the fronds, signaling they are ripe. An easy way to do this is to cut off a frond when its spores are beginning to darken in color. Leave the frond in an open paper bag or on top of a piece of paper (indoors, where the spores won't get blown away) and wait for the spores to fall. You want to be sure they are fully mature and fall off on their own.
- Fill a flat or another container with sterile, moistened potting mix designed for ferns. Shake the spores off the paper or bag directly on top of the mix and press gently, so the spores make good contact with the soil.
- Mist the surface of the potting mix, to moisten the spores and keep them in place.
- Cover the container with plastic and place it in a tray filled with 1 to 2 inches of water. Move to a warm spot, with indirect sunlight.
- Keep replacing the water in the tray until you see signs of growth. This can take 6 to 12 weeks, so be patient and don't let the soil dry out.
- The first thing you will see will be small heart-shaped shoots called prothalli. These can be gently lifted out of the container and moved into individual pots filled with damp, sterile fern potting mix. Leave the transplants uncovered, but keep them moist.
- Once the prothalli begin developing fronds, they can be slowly hardened off and transplanted outdoors.
Propagating Ferns From Stolons
A second way to propagate ferns is by planting the stolons—long, fuzzy string-like structures growing from your fern. These are stolons or runners, and you can propagate ferns by layering them on the soil.
Pin the stolen to the nearby soil with a U-shaped landscape staple or a small rock. Keep moist and in a few weeks the stolon should root and send up new growth. When that happens, cut the stolen from the mother plant. This new plant can now be dug up and transplanted to a new location.
Propagating Ferns by Division
When fern fronds begin to get smaller, or if you notice a bare center in a clump, it is time to divide them. Some ferns form visible crowns, and while others grow as mats of fibrous roots. To divide, dig up the entire clump and cut 6-inch squares of the most robust growth. Each piece should have at least one growing tip where fronds are sprouting. Replant the pieces at the same depth as the original plant, then water them in thoroughly.
Growing Ferns Indoors
Ferns make lovely houseplants, but the humidity in homes is often too low for some ferns to thrive. This is especially true in the winter when the heat is on. Misting the plants will help improve humidity levels, as will placing their containers on a tray filled with pebbles and just enough water to reach the bottom of the fern's pot.
Some ferns that can better handle low humidity include:
Most ferns have no serious problem, other than slugs that may feed on the fronds. Fight them with commercial slug bait or diatomaceous earth spread over the ground around the plants.
Ferns that get too much sun, or are growing in subpar soil, will be weak and won't spread as vigorously.