Nature News: Sweet fern can do something no other plant can (not really)

published June 8, 2020 by and in the Portsmouth Herald, York Weekly, Foster’s Daily and other seacoast newspapers

Sweet fern fruit looks like a little bristly tribbles Sue Pike photo

My early morning dog-walk follows the road behind my house, up the hill to an old abandoned gravel pit carved out of a long ridge of gravel, an esker, formed in tunnels underneath the glaciers of the Laurentide ice sheet that covered Maine as recently as 12,000 years ago.  If you are a plant, these sandy deposits can be hard to grow in–the gravelly-sand is too well drained and therefore dry.  And, because the soil is still being rebuilt after those glaciers scoured our area clean, there isn’t a lot of organic material to provide the nutrients essential to life.  Among a handful of plants that do well with these conditions is sweet-fern.  It has been leafing out over the past few weeks, and as with many of my favorite seasonal plants I feel like I am welcoming it back after a long absence. 

Sweet-fern is fairly common around here and is a good plant to get to know. It is easy to identify and has some fascinating traits.  Sweet-fern is not a fern; it is a member of the bayberry family.  The ‘fern’ part of its common name comes from the leaves’ resemblance to the foliage of a fern.  Sweet-fern is, in fact, the only woody plant around here with fern-like foliage (a helpful clue when trying to identify).  

The ‘sweet’ part of its common name refers to the smell given off by crushing the leaves, to me it smells like it’s in the bayberry family-spicy and sweet.  Others describe it as a turpentine-like smell–not so sweet a description, but the odor does have some of that resinous resonance.  That distinctive smell is produced by glandular hairs on the leaves, when crushed the pungent smell they produce can be detected quite a large distance away….it is heavenly walking through a field of sweet fern on a hot summer day.  The odiferous nature of sweet fern has led to it being used as an insect repellent throughout human history.  Native people used it in smudge sticks to repel insects.  Colonial settlers scattered it on the floors of their cabins to deter pests. If you go online you will find numerous recipes using sweet fern in herbal insect repellents.  

One of my favorite things about sweet fern is its amazing ability to colonize barren sandy soils.  If you want to find some sweetfern check along your nearest powerline right-of-way, road edges, sand pits and more natural habitats like rocky outcroppings.  These relatively barren lands are where it thrives.  Plant some in a richer environment and it will be outcompeted by other plants.  

Sweet-fern does so well in these desolate places because they form symbiotic relationships with bacteria in their roots that can turn atmospheric nitrogen into a usable form.  Not many plants (and no animals) can do this.  Nitrogen makes up 78% of the Earth’s atmosphere, we breathe it in with every breath, yet we can’t access that nitrogen.  Nitrogen is essential for building proteins which are, in turn, necessary for life.  Legumes (beans and peas) are famous for having symbiotic relationships with rhizobial bacteria that live in root nodules, fixing nitrogen into usable forms in exchange for sugars and a variety of minerals.  This is why farmers will often rotate nitrogen-fixing crops like legumes with nitrogen-consuming crops like corn-the corn sucks up all the nitrogen from the soil, the legumes pump it back in.  Non-leguminous plants, sweet-fern for example, do the same thing with a different group of bacteria-members of the genus Frankia. Dig up a root and you’ll see the nodules (little bumps) that house the nitrogen-fixing bacteria.   I can’t stress how critical nitrogen-fixing is-no other living organism can do this–just bacteria, lightening and fertilizer factories.  Plant some sweet-fern and it will add nutrients to the soil, eventually enabling other plants to grow.