By Dr. Bob Gilbert
While at Ammons Nursery in Tuckasegee recently I spotted a fern like plant with woody stems that was new to me, Comptonia peregrina or Sweet Fern. From the Internet I discovered it is not a true fern but belongs to the bayberry family. It is a small shrub or a shrublet. The leaves have glandular hairs that when crushed give off a fragrance. The leaves resemble ferns in outline form, hence it’s common name. In fact it is the only woody plant in North American with fern like foliage. It was no surprise to find the genus name Comptonia was created in honor of someone who had never seen it, Henry Compton the Bishop of Oxford England from 1675-1713, an avid gardener and horticulturist. Peregrina means migratory. Sweet shrub is a spreading plant that travels by under ground roots called stolons; it is stoloniferous as they say.
I found an enlightening article Bulldozers and Bacteria: The Ecology of Sweet Fern by Peter Del Tredici published in Arnoldia 1999 Fall. Sweet Fern only grows to 3 to 4 feet, likes dry sunny sites, exposed mountain slopes, pine barrens, highway banks or any land that has been cut over or disturbed. It is native here in western North Carolina, hardy from Zones 2-7. This intrigued me further. We have been trying to get things to grow in the cuts that were created when we built our road. Del Tredici even says that Sweet Fern has a “pioneering role of a colonizer of disturbed soils.” Another curious fact is that Sweet Fern has nodules on its roots that are inhabited by nitrogen fixing bacteria. These bacteria pull nitrogen out of the air thus improving soil.
Sweet Fern blooms are small and not showy. Seeds are in a nut and are very difficult to germinate. After examining thousands of colonies Del Tredici never found one wild seedling until he found an area that had recently bulldozed. He speculated that seeds had been buried for a long time. Soil disturbance after a long rest stimulated the seeds to germinate. Sweet Fern colonizes by underground roots (stolons), thus it has amazing potential as a “low maintenance, naturalistic plantings along highway bankings and power company rights-of-way.” according to Del Tredici. He comments that 4-6 inch root cuttings planted in the spring will produce a weed resistant canopy within three to six years.
If this plant is so wonderful why is it not used often or better known? Even Del Tredici did not know until after he published his bulldozer article that Sweet Fern is an alternate host for a fungus Cronartium comptoniae, sweet fern blister rust. Rusts are a group of fungi that require two different hosts to complete their life cycle. This particular rust requires pines that have bundles of two or three needles. The alternate hosts are sweet fern and swamp myrtle or sweet gale. The rust can damage pines significantly but hardly has any effect on the alternate hosts. The most susceptible pines are Jack and Lodgepole pines found far north and into Canada. Pitch pines can also be affected but we have very few pitch pines here. It barely damages pines over 4-5 years old. It mainly affects pine seedlings. So the question remains is it safe to plant Sweet Fern here? Dirr in his Manual of Woody Landscape Plants states ‘there are no serious diseases affecting Sweet Fern.’ He either did not know about the rust, which is highly unlikely, or the effects of it are too insignificant to mention.
Regarding the safety of growing sweet fern Macon County Extension Agent Alan Durden referred me to Ryan Blaedow a forester with the North Carolina Division of Forest Resources. He responded with “it is not a problem in southeastern US.” He also confirmed that this rust is only a problem for seedlings and small trees. Sweet Fern can be safely planted in our area. I would add however if you live within 1 to 2 miles to a pine tree nursery I would ask what species are being grown there to male sure this rust will not effect that crop. The rust spores are spread by wind but no further than 2 miles.
Dr. Bob Gilbert’s articles are being reprinted with the permission of the Franklin Press in Franklin, North Carolina.