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Natural Organic Turf Fertilizers
James Murphy, Ph.D., Turfgrass Management, Rutgers

Q. What are the recommendations for homeowners who want to use natural organic fertilizers on their lawns?

A. "Natural Organic" fertilizers are certainly acceptable materials to use for maintaining lawns; note that these were the only materials available for fertilization up to about the 1940's.

Since many people are most familiar with the synthetic fertilizers, they probably need to be educated about the meaningful differences between 'organic' and synthetic. 'Natural organics' will not provide good cool weather growth response. 'Natural organic' fertilizers require breakdown of the organic nitrogen compounds (proteins and amino acids) by microbes before plants can effectively utilize the nitrogen. Microbial breakdown slows dramatically as soil temperature fall into the 50's and below. Thus, nitrogen availability from 'natural organics' will be quite low during the cooler times of the growing season. This may be a drawback when you want to encourage late- or early-season growth of the cool-season recovery from severe summer damage. 'Natural organics' are a better fit for clients that are most concerned with warmer weather appearances, not cool weather appearances.

Natural organics are relatively safe since the nitrate leaching potential and salt index are low. A low salt index translates into low burn potential on the turf when the fertilizer is misapplied.

'Natural organic' fertilizers are thought to increase organic matter content of the soil. However, this is difficult to defend with most products since the amount of organic matter added to the turf/soil is rather small. For example, a 50-lb lag of 10-5-0 (hypothetical) fertilizer would cover 5,000 sq.ft. at 1-pound of nitrogen per 1000 sq.ft. Therefore, 1 application would increase the soil organic matter content by 0.02% [(50/230,000) x 100] if the entire 50-lb where organic matter. The growth of the turf does more to add organic matter to the soil than many 'natural organic' fertilizers. Research studies typically show that soil organic matter under turf does not increase any more with natural organics than synthetics. If clients want to increase the soil organic matter, they are better off topdressing the lawn with a leaf/yard waste compost or another high quality compost. As much as 1/2-inch of screened compost can be worked into the turf each spring and fall to improve soil organic matter at the surface. At this high a rate the compost works well as fertilizer too. A Rutgers research study showed you could reduce nitrogen input by 50% or more with a spring and fall topdressing (3/8-inch deep) of leaf compost and still achieve above average turf quality on Kentucky bluegrass.

Another issue that is often 'oversold' is the potential for pest control, particularly diseases. The claimed benefits are not astounding in my assessment, if present at all. So be wary of recommending these materials for that purpose; very often, clients are likely to be disappointed by the realized 'benefits'.

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