Managing algae in the greenhouse

Spring rains may result in water seeping into greenhouses. Warm, humid conditions provide an ideal environment for algae growth. Univ. of Mass. extension floriculture specialist Tina Smith and Univ. of Conn. extension horticulture and greenhouse IPM specialist Leanne Pundt said algae growth on walkways, under benches and in pots or plugs is a problem for many growers.
Excessive algae growth on walkways can be a safety hazard for workers. Algae growth on greenhouse coverings can reduce light levels. It competes with desirable plants for nutrients and forms an impermeable layer on the growing medium surface that can interfere with water penetration.
During plug production, slow growing plants can be especially sensitive to algae buildup. Algae are a food source for both fungus gnats and shore flies.
All surfaces should be kept free of plant debris and weeds that can be a nutrient source for algae growth. A physical weed barrier can help to prevent both weed and algae growth.
Proper ventilation reduces the amount of moisture in the greenhouse. Horizontal airflow fans help regulate greenhouse temperatures and reduce excess condensation. Retractable roof or open roof greenhouses provide good ventilation.
Avoid overwatering plants, especially early in the crop cycle. Select a medium that is appropriate for the plants being grown.Allow the upper surface of the medium to dry out between waterings. Over-watering plants frequently leads to algae and liverwort buildup on the surface of the growing medium.
Irrigate the plants only as needed to prevent excess puddling of water on floors, benches and greenhouse surfaces. Porous concrete floors limit the development of excessive moisture. The greenhouse floor should be level and drain properly to prevent the pooling of water.

Pictured: Excessive algae growth on walkways can be a safety hazard for workers.
Photo by Leanne Pundt, Univ. of Conn.