How to identify and manage nostoc in nurseries and greenhouses – Part 1

Identifying nostoc early in container production can help growers develop an effective control plan. Part 1 discusses the biology and identification of nostoc.

A green, mossy-looking substance growing on a hard, gravel surface next to potted nursery plants.
Photo 1. Gelatinous mass of nostoc growing on hard surface of nursery where irrigation is frequent. Photo by Debalina Saha, MSU Horticulture.

Nostoc, sometimes known as star jelly or witch’s butter, among other names, is a genus of cyanobacteria or blue green algae that can proliferate in almost any environment. It can infiltrate and colonize almost any ecosystem, including polar, tropical, aquatic, terrestrial environments and more.

Colonies of nostoc are made of long filamentous chains, or strands of cells that continue to elongate without separating and can form both microscopic groups under the soil as well as visible mats on a surface (Photo 1). These colony mats can desiccate completely in dry conditions. Dry nostoc can easily be blown around in the wind and spread to undesirable locations. When moisture returns, colonies swell back up into dark green, gelatinous blobs. This form can be introduced to new environments on poorly sanitized tools, shoes and clothes, or by transferring infected plants or growth media between locations. For these reasons, it is incredibly difficult to control the spread and movement of nostoc colonies inside a greenhouse setting.


Nostoc can be found growing in many different habitats including lawns, garden beds, athletic fields, paved surfaces, 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, according to “The continuing battle against nasty Nostoc” by Jennifer Parke. Greenhouses 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 allow it to thrive, according to the “Nostoc” factsheet by N. Jordan Franklin.

Cellular components

As a cyanobacteria, nostoc are photosynthetic single-celled organisms that can live in a multicellular state called a filament. The jelly-like nostoc mats seen in the greenhouse and nursery are made up of these filaments. Living in this state allows the individual cells to share nutrients and cover a large area in search of sunlight, water and nutrients. A typical cell is considered to be vegetative, but according to “A biological introduction to cyanobacterial mats” by Luisa Santamaria, there are several different types of cells that they can differentiate into under specific pressures:

  • Heterocysts: specialized cells that perform nitrogen fixation.
  • Hormogonia: motile filament fragments formed under extreme drought or heat pressure that can move the cyanobacteria to a new location.
  • Akinetes: very resilient spores that also form under extreme conditions and remain dormant until more favorable environmental conditions and a new filament can be produced.

Nostoc as a beneficial organism

Nostoc can be a helpful organism in some situations, sharing nutrients with other organisms and maintaining soil moisture. This kind of cyanobacteria is photosynthetic, making them attractive to other organisms for symbiotic relationships with an exchange of energy. The additional ability of the nostoc genus to fix atmospheric nitrogen and sequester atmospheric carbon makes the nostoc mat itself a good substrate for other organisms on terrestrial surfaces on which they otherwise could not inhabit.

Finally, the presence of nostoc over the top layers of soil or growing media around a plant can create a mulch-like effect reducing water evaporation and temperature fluctuations. This increase in the soil moisture potential significantly improves a plant’s ability to remain hydrated during periods of drought.

Harmful effects of nostoc in greenhouse and nursery production

While nostoc can have symbiotic relationships with other organisms, there is still potential for competition between organisms sharing the same resources. Although it is true that nostoc contributes to nutrients in the soil, it is also responsible for using those resources to increase its own presence. The possible overgrowth of nostoc threatens greenhouses and nursery production due to competition for light and moisture as well, depending on the specific morphology of the plant in relation to the growth of nostoc. Contamination of greenhouses and nurseries can also create large areas of very slippery biomass that poses a safety hazard for growers, greenhouse/nursery workers and clientele at the site. Nostoc contamination can also be aesthetically displeasing. For greenhouses or other nursery sites sell ornamental or other agricultural plants, a heavy nostoc infestation has the potential to cause a large financial loss.


Did you find this article useful?