The 2011 ASHS Annual Conference

Annual plants grown for the bedding plant market use soilless media and water soluble fertilizer for optimal production.Phosphorus fertilizer in runoff poses an environmental problem. When elevated levels of phosphorus are present in surface water, algal blooms often result. Algal blooms use up oxygen, resulting in low oxygen levels (hypoxia) for fish and other aquatic life. Some states are already regulating or banning the use of phosphorus in the landscape industry.Mycorrhizae are a group of soil-borne fungal organisms that can develop a symbiotic relationship with certain plant species. One of the beneficial results is increased phosphorus uptake. They occur naturally, and are commonly present in natural areas. However, greenhouse production of bedding plants is an artificial environment which excludes such soil-borne organisms. Soilless media is composed of a blend of organic and mineral ingredients that would not normally be inoculated with mycorrhizae or other naturally-occurring soil-dwelling organisms.Mycorrhizae products are available for adding to soilless media, and some soilless media products are formulated with mycorrhizae in them. However, mycorrhizae may not survive under the conditions present during media shipping and storage. Mycorrhizae products are dated for freshness and must be used within a specified time. They also must be stored under optimal conditions to maintain viability. Marigold (Tagetes patula) and Zinnia (Zinnia pumila) seeds were germinated in two types of soilless media: pre-packaged and mixed on-site and seedlings were evaluated for their response to two commercially available mycorrhizae products: Mighty Myco and Mycormax. The former product was mixed into the soilless media before planting and the latter product was applied as a drench after seeds were planted. Both products were used at the recommended rates. Shoot and root weights suggested that for both marigolds and zinnias, roots were larger on the control treatments as compared to both mycorrhizae products. Zinnia shoots were largest with Mycormax, but marigold shoots were largest on control plants. Tissue testing for essential nutrients indicated mixed results with respect to phosphorus uptake in marigolds and zinnias when comparing the two soilless mixes and the two mycorrhizae products. Mixed results were also found with respect to other essential plant nutrients.