There are many kinds of Adiantum, commonly called Maidenhair Ferns. Most of them are natives of tropical countries, but two are hardy and can be grown outside in the North. One hardy kind is A. pedatum, native of North America. Its graceful fronds grow 18 to 24 inches long. They flourish in shade and woodsy soil made by adding leaf mold and sand. This plant is great for clumping in cool, shady spots in the wild garden and rock garden. A. Capillus-Veneris is another fern that's hardy, it's found wild in North America, Europe and South America. The most popular tender kind is A. cuneatum (Delta Maidenhair Fern), native of Brazil. It has many beautiful varieties such as, elegantissimum, gracillimum, grande and Pocottii. They make suitable pot plants and the fronds are used for cutting. The young ones will droop quickly, so immerse them in water for 24 hours before use. Other kinds of Maidenhair Fern are A. macrophyllum, which has very large leaflets (pinnules) and A. tenerum Farleyense, which has large fronds on stalks, 18 to 24 inches long. The latter needs a warmer greenhouse than the others do; a minimum temperature of 60 degrees is necessary.
Repotting is done in March or April, as soon as the new fronds begin to uncurl. Remove the crocks and loose soil with a pointed stick and set in slightly larger pots filled with equal parts of peat moss, leaf mold, and loam with an addition of coarse sand and a few small pieces of charcoal. Press this firmly with the fingers, not a potting stick. By repotting yearly, large plants may be grown in 10-inch pots, but those in 5-inch pots are most useful. When they're in larger pots, Maidenhair Ferns can be kept growing actively for several years by top-dressing them with fresh compost in March and by applying weak, liquid fertilizer every week from May to August. With the onset of fall comes a decrease in the water supply. From September to March, very little water should be given because this is their resting period, but the soil should never be very dry. The tender kinds need a partially shaded, heated greenhouse (minimum temperature of 50-55 degrees) that has diffused sunlight, but not too dull. The young fronds will be scorched if they are subjected to harsh sunlight and too much shade makes very weak growth. The atmosphere must be humid during the growing season. Do not sprits the foliage because moisture will collect between the small fronds and cause them to damp off. Maidenhair Fern can be grown indoors in a shady window, but will usually deteriorate within a few months unless they're returned to a warm, humid greenhouse for a time, or are enclosed in a terrarium.
Maidenhair Fern are increased by division or spores. They may be divided in the spring as soon as the fronds begin to uncurl. Separate the plant into two or three pieces and repot separately. If a large number is desired, wash away the soil and separate them into single rooted pieces and set in a flower pan filled with moist sand. Place them in a propagating case and when they are well rooted they are potted individually into 2-inch pots. Propagation by spores is an easy and reliable method. When the spores are ripe, which is when they are dark brown or yellowish brown, a frond is set in a paper bag and hung in a dry place for several hours to allow the ripe spores to fall to the bottom of the bag. Sprinkle these thinly on the top of finely sifted compost that is in small pans filled halfway with crocks. It is wise to sterilize the compost, crocks and pans by baking before planting the spores. Set a pane of glass over the pots, which are then set in saucers of water. Place the pots of spores in a greenhouse with the required temperature and cover with paper. The prothallia (prothallia are the thin, green, heart-shaped structures that bear a number of root hairs that attach to the soil and extract nourishment) that develop from the spores are pricked out in small clusters and placed half an inch apart in pans of sifted compost. When they're visible as tiny plants just press them into the surface of the compost. They must be kept moist by standing them in water. Don't water them from above until they develop their first small fronds. When they're large enough they can be potted in 3-inch pots and, later, into larger ones. Ferns aren't cross-pollinated as flowering plants are. The spores of two or more kinds are mixed and planted together and hybridization takes place naturally in the prothallia stage. The male element from the prothallia of one kind swims in the film of moisture and enters the female structure on the prothallia of another kind of fern, and fertilization takes place.