Polystichum - Christmas Fern, Holly Fern, Shield Fern
DESCRIPTION: These tender and hardy Ferns (Holly Ferns) are found in many parts of the world, especially in tropical America, North America, Europe, tropical Asia, Japan and South Africa. The fronds of these Ferns vary in length from 2 to 4 feet. P. aculeatum 'Pulcherrimum' has arching, evergreen or semi-evergreen, rigid fronds that are delicately cut into toothed segments. These feathery fronds are bright green maturing to dark green. P. setiferum 'Divisilobum' has arching, bright green, narrowly oval fronds that are finely divided into soft-textured segments. They are covered with white scales as they unfurl. P. setiferum proliferum is a dainty plant with bright green, oval fronds finely divided into mossy segments. They are also clothed with white scales as they unfold.
POTTING: Hardy - These Ferns should be grown in moist, fibrous soil that is well-drained, in a partially shaded location. These Ferns look very handsome when grown in rock gardens.
Greenhouse - These Ferns need a minimum temperature of 50 to 55 degrees. The best soil mixture consists of equal parts of loam, peat moss and leaf mold, with a generous amount of sand. Repotting should be done in February or March. Take the plants out of their containers and remove the crocks and loose soil from the roots. The pots in which the Ferns are to be planted need to be clean and if new, soaked in water and allowed to dry prior to use. They need to be well drained with broken crocks; these should be covered with the rough siftings from the soil or with leaves to prevent the potting soil from running down and clogging the drainage. The soil must contain the correct amount of moisture. To test this, take a handful of soil and squeeze it firmly. When the hand is open, the soil should remain together, but fall apart at the slightest touch. When potting, firm the soil moderately with the fingers, not rammed with a potting stick. Take care not to overwater these Ferns, especially before their pots are filled with healthy roots. Keep the soil moist throughout the summer and only water when the soil begins to dry the rest of the year (at which time it should be watered thoroughly). Keep the atmosphere humid by keeping the area around the pots moist, but not the fronds. Keep shaded from direct sunlight, except during the winter.
PROPAGATION: These Ferns may be divided, or bulbils may be planted in the spring. Spores may be sown in the summer. 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.
VARIETIES: Hardy - P. aculeatum & var. Pulcherrimum, angulare, cristatum, grandiceps, proliferum, imbricatum, plumosum; P. munitum (Giant Holly Fern); P. setiferum & var. Divisilobum; P. setiferum proliferum; P. acrostichoides (Christmas Fern); P. Braunii (Shield Fern); P. Lonchitis (Mountain Holly Fern).
Greenhouse - P. adiantiforme; P. aristatum (East Indian Holly Fern) & var. variegatum; P. tsus-simense; P. viviparum.
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