The sudden appearance of an unsightly, gelatinous growth on lawns, gravel paths, or walkways often signals an infestation of Nostoc commune. This organism, frequently mistaken for a type of algae or fungus, is actually a terrestrial cyanobacterium, sometimes called blue-green algae. Its presence can make surfaces slick and unappealing, creating a persistent landscape problem. This guide provides practical solutions for immediate elimination and long-term strategies to prevent its return.
Identifying Nostoc
The most distinguishing characteristic of Nostoc commune is its drastic change in appearance between wet and dry conditions. When hydrated, typically after rain or irrigation, it swells into a rubbery, dark green to bluish-black mass resembling jelly or mucus. This gelatinous quality is due to a thick, polysaccharide-rich sheath surrounding the bacterial filaments, allowing it to absorb and retain large amounts of water.
When the moisture evaporates, the organism shrinks significantly, drying into a thin, brittle, black, and crusty layer. This ability to desiccate and survive extreme drought is a key feature of the cyanobacterium. While often grouped with algae due to its photosynthetic nature, its prokaryotic cell structure technically classifies it as a bacterium.
Conditions That Encourage Nostoc Growth
The proliferation of Nostoc is directly tied to persistent moisture and poor surface conditions. The organism thrives where water pools or drainage is insufficient, such as in compacted soil, frequently irrigated lawns, or poorly sloped hardscapes. This consistent water saturation allows the cyanobacterium to swell and actively grow, creating noticeable mats.
Compacted soil is particularly conducive to its growth because it increases surface water retention and limits the health of competing plants. Nostoc possesses specialized cells called heterocysts that allow it to fix atmospheric nitrogen. This nitrogen-fixing ability means the organism can flourish even in environments with low soil fertility. High levels of phosphorus in the soil or substrate can also promote its growth.
Methods for Immediate Eradication
Addressing an existing Nostoc infestation requires a combination of physical removal and chemical treatment, targeting hydrated colonies for effectiveness.
Physical Removal
Physical removal is a necessary first step on hard surfaces like patios or driveways, where the gelatinous masses can be scraped off or carefully lifted. For dry, crusty colonies, using a stiff-bristled broom or blower can help break up the material. However, this action risks spreading reproductive fragments to new areas.
Chemical Treatment
Chemical treatment must be applied when the organism is fully saturated and swollen to ensure absorption through the protective sheath. Homeowners can use diluted household bleach (sodium hypochlorite) on hard surfaces. Alternatively, solutions containing baking soda (sodium bicarbonate) can be applied to the mats, which alters the surface pH and disrupts the organism’s structure.
More robust options include algaecides containing active ingredients like sodium carbonate peroxyhydrate or hydrogen peroxide/peroxyacetic acid, which are effective oxidizers against cyanobacteria. These commercially available products are generally non-selective and should be used with caution around desirable plants, always following label instructions. Repeat applications over several weeks are often necessary to eliminate newly emerging growth.
Preventing Recurrence Through Site Management
Long-term control of Nostoc depends on modifying the environmental conditions that support its growth. The primary focus must be on improving drainage to eliminate the standing water the cyanobacterium requires. On lawns, this involves mechanical aeration to reduce soil compaction, allowing water to penetrate the soil profile more quickly.
In garden beds or areas with compacted soil, amending the area with coarse sand or organic matter helps create a more porous structure that encourages rapid water percolation. For hardscapes, fixing any grading issues that cause water to pool is essential. Reducing the frequency of overhead irrigation is another important step, ensuring the soil surface dries out completely between watering cycles. Increasing sunlight exposure by trimming nearby shrubs or trees also helps the ground dry faster.