The greenhouse conditions, with its high moisture, controlled temperature, and light, favor the growth of the lower group of plants, including the algae, mosses, liverwort, and Nostoc. All of these are considered weeds and can compete with the ornamentals grown in containers for water, nutrients, and space. These can even prevent the irrigation water and fertilizers from reaching the root zone of the ornamentals as they have a mat-forming nature and can cover the container surface. As a result, the growth of the ornamentals can get reduced. In addition, these can become very slippery once they absorb moisture from irrigation water and can cause safety issues for the greenhouse workers in the walkways.
Commercial bleach (sodium hypochlorite), bromine, copper, peroxy-acetate, and quaternary ammonium compounds can be used to control these slippery weeds inside the greenhouse. But these chemicals can only be applied to the hard non-living surfaces such as walkways, benchtops, and empty pots. If these chemicals come in contact with the plant issues, they can cause severe damage. Algae can be controlled in the cooling pads with chemicals, especially the quaternary ammonium compounds. Organic mulch, such as rice hull and pine bark, can be applied to the containers at a depth of 1-2 inches, depending on the pot size, to control the liverwort and moss growth. Also, strategic fertilizer placement can help reduce the growth of liverwort in container production. Trials conducted at Michigan State University have shown that when controlled-release fertilizer is placed as subdressing at a depth of 2-3 inches from the soil surface, can provide good control of liverwort than incorporating or top dressing the fertilizer in the containers.
Preventative measures are recommended, which include keeping the walkways dry as much as possible and making sure that runoff from fertilizer applications is minimal, maintaining proper drainage, and avoiding overirrigation. Periodic cleanup, checking the new shipments and liners, and using clean media and equipment are highly recommended.