Glyphosate is the active ingredient in many popular, broad-spectrum weed control products, such as Roundup. Moss, a non-flowering plant that frequently appears in lawns, on roofs, and between paving stones, can be a frustrating problem for many homeowners. The direct answer to whether glyphosate is effective against moss is generally no, as the herbicide is largely inconsistent or completely ineffective. This lack of efficacy stems from fundamental biological differences between moss and the vascular plants that glyphosate is designed to kill.
How Glyphosate Works on Target Plants
Glyphosate functions as a systemic herbicide, meaning it is absorbed by the foliage and translocated throughout the plant’s entire system, including the roots. It targets the shikimate pathway, a metabolic process present in most plants and some microorganisms. The herbicide works by inhibiting the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), a component of this pathway.
The shikimate pathway produces three aromatic amino acids: phenylalanine, tyrosine, and tryptophan. These amino acids are necessary for the plant to create proteins and compounds required for growth and survival. By blocking their production, glyphosate starves the plant of resources, leading to cessation of growth and eventual death. This systemic action makes it highly effective against most broadleaf weeds and grasses.
Why Moss Resists Glyphosate Treatment
Mosses are classified as bryophytes, which are non-vascular plants fundamentally different from the grasses and weeds glyphosate controls. Unlike vascular plants, mosses lack specialized tissues like xylem and phloem for water and nutrient transport. This anatomical difference is the primary reason the systemic action of glyphosate is ineffective.
Even if absorbed on the surface, the herbicide cannot efficiently translocate throughout the entire moss organism to reach every cell. Mosses also lack true root systems, instead using simple root-like structures called rhizoids primarily for anchoring. While mosses do possess the shikimate pathway, their reliance on it and the mechanisms for cellular uptake differ significantly from those of vascular plants. Without the internal transport system to move the chemical, glyphosate cannot achieve the sustained inhibition required to kill the moss entirely.
Effective Alternatives for Moss Removal
Since glyphosate is not a reliable solution, effective moss control requires alternative chemical treatments or changes to the growing environment. One successful chemical option involves iron-based products, such as ferrous sulfate, which rapidly kills moss by oxidizing it. The treated moss quickly turns black, allowing for easy manual removal, though these products can unfortunately stain concrete or stone surfaces.
Another effective chemical approach uses soap-based solutions containing potassium salts of fatty acids. These act as contact killers, quickly breaking down the moss’s protective outer layer.
Beyond chemical treatments, altering the conditions that allow moss to thrive offers a long-term solution. Moss flourishes in damp, shaded, and often acidic environments. Improving drainage and increasing air circulation can significantly reduce its growth. Physical removal using a rake or scraper is effective for immediate control, and cultural practices like aeration and adjusting the soil’s pH with lime help favor grass growth over moss.