Got Slimy Weeds in Your Greenhouse? They May Be Nostoc

Posted by Brian Sparks|June 15, 2023

Nostoc is a genus of cyanobacteria or blue-green algae that can proliferate in almost any environment. Its ability to withstand any weather, including polar, tropical, aquatic, terrestrial environments, and more means it can infiltrate and colonize almost any ecosystem.

Colonies of Nostoc are made of long filamentous chains, or strands of cells that continue to elongate without separating and can go on to form both microscopic groups under the soil as well as visible mats on a surface. These mats of colonies have the ability to desiccate completely in dry conditions, and then swell back into their telltale dark green, gelatinous blobs when returned to the presence of moisture.

A recent e-GRO alert from Michigan State University highlights why it can be incredibly difficult to control the spread and movement of Nostoc colonies inside a greenhouse setting. When dry, it can easily be blown around in the wind and spread to undesirable locations. When wet, it can be introduced to an environment by poor sanitation of tools that are used offsite, walked in on someone’s shoes or clothes, or spread by transferring infected plants or growth media between locations.

Nostoc can be found growing in many different habitats including garden beds, container nurseries, and greenhouses. They can survive in dry conditions, but for long-term survival they require a wet environment. Hard surfaces like the concrete in a greenhouse or compacted ground of a nursery are perfect environments because the frequent irrigation stands in pools on the poorly drained ground. Greenhouses in particular, provide perfect conditions for its fast growth and production of biomass due to high humidity, high temperatures, and high light levels in addition to frequent irrigation. Finally, phosphorous is the most limiting nutrient for nostoc, so environments high in phosphorous are likely to attract it.

For more information, including how Nostoc can be both a beneficial and harmful organism, as well as management strategies, check out the original e-GRO alert here.