Most hardy ferns are able to grow as far north as the Great Lakes, into New York State and along the Atlantic coast into Canada (zone 4). Some types of ferns are even hardier, tolerating winter temperatures lower than -20°F and thriving in northern New England, Minnesota and North Dakota.
Locating and Planting
Although there are some ferns that thrive in the sun along roadsides and pastures, most ferns like moist, woodsy places that are somewhat shady. Typically ferns prefer filtered sun or "high shade" which is fairly bright. They are not happy in very deep shade. A good site for ferns is the north side of a building, under trees or shrubs, or in the shade of a wall or rock ledge. However, because Norway maples are particularly dense with a shallow root system that monopolizes soil nutrients and water, avoid planting ferns beneath them. Their shade conditions determine how much moisture they need, but ferns do need moist soil that is well-drained and somewhat acidic (pH 5.0 to 6.0). Add humus, organic material such as chopped leaves, peat moss, or composted sludge if it is available to improve the moisture holding capacity of the soil.
If possible, plant young ferns in the spring before their fronds completely unfurl. Under normal conditions, ferns can be moved as late as mid-June, if necessary. Ferns usually come bare root from the garden center or nursery. Keep their roots moist until planting by wrapping them with damp paper towels or newspaper; then place them in a plastic bag and store them in a cool place. At planting time cut off any broken fronds. If the roots are skimpy, cut all fronds back one-third to minimize water loss from leaf surfaces. Dig a hole slightly larger and deeper than the root ball. Ferns that have rhizomes for roots, must be planted shallowly. Score a 1 inch deep trench in the soil. Lay the rhizomes in the hole so they are level (horizontal) and naturally oriented. Set them just below the soil surface, assuring that the crown of the plant is slightly above the soil. Firm the soil gently over the roots and water. Place large ferns, like the ostrich fern, 3 feet apart, but most can be spaced at 12 to 18 inch intervals. Give shade-loving ferns a little more space than those grown in sunny areas.
The easiest way to grow more fern plants is to divide existing clumps after 3 or 4 years when they become large. In the spring gently lift the plant mass up from the soil with a spade. Shake the soil from the roots, exposing them. Carefully pull them apart into several smaller fern clumps. Tightly tangled roots may have to be cut apart with a sharp knife. Disturb the fronds as little as possible. Plant the separate ferns carefully, as described above.