FERNS
Ferns are among the world's oldest living plants. They have been around for more than 350 million years and are lower on the evolutionary scale than seed plants. Only algae and mosses are older. Long before the appearance of man, great forests of giant ferns covered the earth. Today all that remains of these dense jungles are vast beds of coal formed by the decay of the plants when they were submerged by floodwaters. Nevertheless, quite a few of the descendants of these prehistoric ferns still thrive, and over 12,000 species have been identified to date.
Ferns were the dominant form of vascular plant until the age of the Dinosaurs, when seed bearing plants came into prominence. There is fossil evidence of ferns as far back as the Devonian Period, which was 416-359 million years ago. The ferns were at their height during the Carboniferous Period, 359-299 million years ago, as they were the dominant part of the vegetation at that time. During this era, some fern-like groups actually evolved seeds making up perhaps half of the fern-like foliage in Carboniferous forests and much later giving rise to the flowering plants. Most of the ferns of the Carboniferous period became extinct, but some later evolved into our modern ferns.
Ferns are perennial flowerless plants that are grown around the world. About the only place they are not found is desert regions and the north and south poles. The true ferns are classified as Pteridopsida and are by far the most numerous of all of the fern-allies. There are nine sub-classes, about 250-300 genera, and over 12,000 different species alive today. Some ferns grow as small as an inch, and are perfect for terrariums, while others can grow as big as trees, up to 50-60 feet. Some common fern types are Boston, maidenhair, staghorn, rabbit's foot, and pteris. Plants in the genus Asparagus such as A. setaceus and A. densiflorus are called ferns, but are not true ferns since they produce seeds and not spores.
Ferns are more complicated in structure than most people would suspect. Their structures, though similar in some ways to those of flowering plants are different enough to warrant a distinctive terminology. The frond is the part of the fern that we see as we wander through the woods; it is the "leaf" of the fern. Fronds vary greatly in size, from tree ferns with 12-foot fronds to the mosquito ferns with fronds only 1/16 of an inch long. Rhizomes on ferns would be comparable to "stems" in flowering plants. Fronds arise from the rhizome. In many cases the rhizome can be inconspicuous or even entirely underground. Rhizomes of tree ferns on the other hand, may be 24 inches in diameter and up to 40 feet tall. Roots are most commonly formed from the rhizomes and usually do not divide once they grow from the rhizome. The roots serve to anchor the plant to the ground and absorb water and minerals.
The reproductive structures of ferns are called sporangia. They are miniature sacks or capsules that produce the dust-like spores that are the "seeds" by which ferns are propagated. The arrangement of sporangia varies greatly in ferns. Most ferns that we see as we walk through the forest have their sporangia on the underside of the frond, arranged in an organized pattern usually associated with the veins on the frond. The "seeds" of ferns are called spores. Normally they are formed in groups of four. Spores contain oil droplets and sometimes chlorophyll in addition to their nucleus. Ferns drop millions, sometimes billions, of spores during their lifetime, but very few ever land in a spot suitable for growth.
The life cycle of ferns may seem complicated, but it has worked quite successfully for millions of years. Though spores come from the fronds of ferns, the fronds do not come directly from the spores. Spores from the parent fall to the ground and with an enormous amount of luck they will find suitable moisture and light. The tiny single-celled organism starts to grow by cell division. Soon orderly arrangements of cells form little green heart-shaped plants or prothallia. These plants go unnoticed by most people as they are only 1/2 inch or less across and lie flat on the ground. This is an independent plant with its own simple root system to provide it with nutrients and water. The prothallium then grows male organs and female organs on its underside. The spermatazoids produced by the male organs will swim via a droplet of water to the egg produced by the female organs. The fertilized egg then begins to grow a sporophyte, the plant that we know as a fern.
Propagation of ferns can be done either from spores or by division. However, division is the most practical method for home gardeners. A fern needs to be divided when either the center of the clump is hollow or dead or the fronds are smaller than usual. You may also divide if you simply want more plants. Outdoor ferns can be divided by separating clumps or cutting off established runners. Generally, division is done every three to five years, and can be done right after the first frost in the fall. Fall transplants should not be fertilized. Ferns may also be divided in very early spring, just as the new growth is emerging, but care must be taken to not damage the delicate new leaves. Those with running rootstocks will send up new fronds if transplanted in any season, but they tend to overrun their sites. Use running rootstock ferns such as bracken or ostrich only where a large, mass planting is desired.
Site selection in terms of drainage and light exposure is critical to the production of high-quality ferns. Ferns require well-drained soil. Sandy soils or humus soils with good surface drainage are preferred. Heavy clay soils should be avoided or amended to provide good aeration and drainage. A woodsy location, with shade, moisture and an organic soil high in leaf mold, is perfect for the majority of ferns. Light intensity is another key factor in site selection for plantings of ferns. Ferns generally prefer indirect light. They are excellent plants for shady areas where other plants will not grow well.
Planting directions vary according to species but, in general, ferns with spreading roots prefer to have their roots barely covered, while central-crown types like the crown exposed or just above the soil surface. Dig a fairly deep hole and put in a mixture of leaf mold, sand, and loam. Oak leaves and compost are good substitutes for the leaf mold. If the soil is acid, limestone may be needed, and a mulch of organic materials is always recommended.
Ferns make a fine background for many flowering plants. They give a delicate and airy quality to a shady garden. Cinnamon, royal, and southern shield ferns will grow in full sun if constant moisture is available. Ferns are ideal for damp, low spots by fences, shady areas under trees, on the north side of houses, and indoors where light is filtered and temperatures are fairly low. Some, of course, are strictly tropical and must be grown in a greenhouse in temperate climates. However many of them will thrive in cool, shady, moist spots, even swampy areas. Some hardy types seem to die under hot dry conditions but spring into life as soon as water is supplied.
For an elegant groundcover in a shady spot, try hay scented, ostrich, sensitive, broad beech, or southern shield ferns. Fine textured ferns contrast nicely with the large leaves of hostas, the shiny leaves of hellebores, and the colorful leaves of heucheras. The deciduous types are especially valuable in filling the empty spaces after spring-flowering bulbs have bloomed. Their fronds hide browning bulb foliage and continue to look good even after the shrubs and trees have put forth leaves and made dense shade. Evergreen ferns can be a garden mainstay right up until snow blankets them. The larger ferns are excellent for filling in around newly planted shrubs and supplying height in good landscape design. So, next time you buy plants for your garden, don’t overlook ferns. These low-maintenance plants are invaluable for shade gardens and will make your landscape look mature and lush.