Equisetum hyemale robustum – Giant Scouring Rush; Giant Horsetail

General Information: Perhaps the most exotic cultivar of the ancient Horsetail lineage. Naturally occurring in wetlands, along riverbanks, near springs, seeps, swamps, and wet fields. The spore-producing structure, called a strobilus or a cone, emerges in April, followed by a fresh flush of stem growth. A large, vigorous form with upright, occasionally zig-zagged, Bamboo-like stems. A point of interest is that the stems, when struck at a low angle by early morning or late afternoon sunlight, appear to glow from within like a Japanese lantern. Decidedly exotic looking, this plant is actually a native.

Cultivation Details: This plant has many uses. Pamela Jones, in the book Just Weeds, describes a concoction of the boiled plant material along with Stinging Nettle (Urtica dioica) being an effective means to control Powdery Mildew infections. The ridges of the stems contain silica crystals, giving a rough texture to the plant. One of the few plant-based sources of silica, the plant’s abrasive properties have been used advantageously by people all over the plant’s native range. Sections of the stem are a traditional abrasive used for shaping woodwind instrument reeds. The common name “Scouring Rush” describes the traditional European practice of scrubbing pots and pans with their stems to remove food residue. Boiled stem segments are also used as a traditional polishing material in Japan. The plant has also been used medicinally by Indigenous Peoples in North America and is an ingredient in some homeopathic preparations as well. Stem segments can be pulled apart to make whistles.

Growing Requirements: Prefers full sun to dappled shade. Requires damp to wet soils. An aggressive spreader that can be contained by rhizome barrier. Tolerates various soil types as long as there is good drainage.

Fun Facts: During the Carboniferous Period (359-299 Million Years Ago), Horsetails covered the planet, often growing to the size of modern trees. Their fossils are found in shale beds near coal deposits, indicating that they were likely the source of carbon that was deposited in that age. Depending on geological conditions, these deposits would become either coal, oil, or natural gas. Their persistence as fossils in the soil was determined by scientists to be a function of microbial evolution at the time – soil microbes had not yet evolved digestive enzymes to break down organic matter. Likewise, living Horsetail plants had developed a concoction of chemical defenses that made them impervious to bacterial and fungal infection, a trait their modern relatives still carry. As a result, when the tree-like stems died back, they left behind immense piles of debris. These eventually caught fire, became charcoal, were buried, and finally compressed by natural processes, ultimately forming the vast carbon-rich deposits that are so highly valued today. Ironically, the fossil carbon from these bacterially and fungally-immune plants is today used to develop plastic – a material which, so far, also cannot be broken down by most soil microbes.