Division is a reasonable and practical option for increasing two types of ferns: ferns with a creeping and/or branching rhizome or those with multiple crowns. Many ferns have long-creeping rhizomes, those "feet" that circle the basket or roam about in the garden. These can be judiciously cut apart, taking care to take a growing tip and roots, and potted up in humusy soil or, if of substantial size, set directly into the garden. Try for 4-in. (10-cm) or even larger clumps, as many species, such as Adiantum venustum, do not like to be pried into small bits. I prefer to do this with a seriously sharp knife in the fall, but others use assorted utensils including a sharp spade and operate in the spring. The latter option is preferred for areas with harsh winters so that the foliage and roots can reestablish during mild weather. Among others, polypodiums, nephrolepis, davallias, gymnocarpiums, thelypteris, some woodwardias, and those masters of long
Plantlets crowd the fronds on Woodwardia orientalis var. formosana at the Miller Botanical Garden.
Stock plants for commercial production, Sundquist Nursery, Poulsbo, Washington. Clockwise from bottom, Blechnum chilense, Adiantum venustum, Blechnum penna-marina, Polypodium scouleri, and Polystichum setiferum 'Plumoso-multilobum'. These ferns all lend themselves to vegetative increase. Photo by Nils Sundquist, Sundquist Nursery.
Multiple crowns suitable for dividing.
rhizomes, dennstaedtias, are all easily multiplied in this manner.
Ferns with short-creeping and branching rhizomes with multiple growing tips are also candidates for division. These are your clump-forming rather than crown-forming types and include such gardenworthy specimens as Athyrium niponicum 'Pictum', Adiantum pedatum, Adiantum aleuticum, most cystopteris and cheilanthes, and a number of dryopteris. Cut these apart by taking a portion of the live growing tip(s) with roots and some fronds. To ease the transition cut back some of the foliage, or do the dividing in the fall or before the appearance of new fronds in the spring.
Stoloniferous ferns with rhizomes on steroids, such as Matteuccia struthiopteris (ostrich fern), will happily go forth and colonize, with new plants appearing at some distance from the parent. These can be dug as individuals and easily reestablished (or graciously given away to a friend in need of instant landscaping). I bought one Matteuccia some 20 years ago, and left it in its pot over the winter. It eventually found a home but not before the stolons escaped from the pot and made their way into the surrounding garden. Every spring two or three babies still doggedly appear at the original site and every spring I still doggedly dig them up.
Surgery of another sort is used to divide ferns with multiple crowns. Some dry-opteris frequently develop offsets most easily observed when the fronds are removed. These are complete circles of coiled crosiers and each can be separated from the parent to produce a new plant. Taking half a circle will produce half a plant and a dreadful visual effect. As these divisions can be quite substantial in size, a good sharp spade or machete-sized blade is the recommended weapon. A kinder way is to place two strong forks back to back and then pry. I usually just carve away offsets from the plant's perimeter. Some growers find it more efficient to work with and divide a young fern as soon as it develops one or two offsets. When these are readily distinguished, they dig the entire
clump, clean it, and cut off the new crowns with an appropriate portion of root material to support the offspring (Archer 2005).
In areas with mild winters, fall is an ideal time to divide, but my friends in colder areas prefer to operate in early spring. With either time line, the foliage should be thinned to reduce stress on the roots. Incidentally, left undivided, these same, multi-crowned plants can form massive specimens that are incredibly handsome, so choose wisely before taking knife in hand.
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