Before choosing a fertilizer for your lawn, there are a few things you should know. First, South Portland’s fertilizer ordinance prohibits the use of synthetic fertilizers except in very limited circumstances.

Organic fertilizer is allowed on established lawns only when a comprehensive soil test indicates a need for nitrogen. That fertilizer must be phosphorus-free unless the soil test also indicates a need for phosphorus. Lastly, if you are re-establishing parts of your lawn, you may use organic fertilizer and phosphorus without a soil test.

Organic fertilizers are displayed below lawn seed on the shelves at Maine Hardware in Portland. Shawn Patrick Ouellette photo/Press Herald Buy this Photo

Organic fertilizers are specified because they build soil health, which in turn, creates healthy plants. But overuse and misuse of fertilizer is detrimental, whether organic or synthetic. This article will help you choose the right fertilizer for your needs, ensuring it is South Portland compliant and will help build healthy, living soils that retain moisture and nutrients.

Organic fertilizers are a benefit to plants and the soil when understood and used correctly. Organic fertilizers are derived from either plant or animal products with little or no processing. Once in the soil, they release nutrients slowly through biological decomposition and mineral weathering. In addition to delivering nutrients, they also provide a food source for the all-important microorganisms in the soil.

Here are some tips in choosing an organic fertilizer after reviewing the results of a comprehensive soil test and its recommendations. All fertilizers list three numbers on the bag that represent the percentages of the weight in the bag of essential primary nutrients for plant growth: nitrogen (N), phosphorus (P) and potassium (K).

This is called the fertilizer analysis and guarantees the amount of total of nutrients listed. These nutrients are always listed in the same order for N-P-K content.

Example: 3-3-2
• 3 represents 3 percent Nitrogen (N), which is essential for growth and cell division.
• 3 represents 3 percent Phosphorus (P), which promotes growth for roots, flowers and fruits.
• 2 represents 2 percent Potassium (K), which helps build cell walls and promotes winter hardiness.

Depending on the source, there may also be some micronutrients in small percentages in the bag. In the example above, the actual amount of nitrogen (N) in a 50-pound bag is 1.5 pounds (3 percent of 50 pounds). Organic fertilizers for the purpose of turf grass (lawns) will also list the amount of square feet that a bag
will cover.

Typically, in the example above a 50-pound bag would cover 2,000 square feet. The result would be 0.75 pounds of nitrogen applied per 1,000 square feet of the lawn. This example would be a good choice for a fertilizer to be used when over-seeding a lawn.

The bag will also list the sources for nitrogen. The following is a short list of organic nitrogen sources:
• Bloodmeal: high in nitrogen, fast release, may burn plants.
• Fish meal: nitrogen and phosphate, medium release.
• Corn gluten: high in nitrogen medium to fast release, make sure it is organic.

The last tip to know about organic fertilizer is that the nutrients are made available for plant uptake by the activity of soil microbes. Incorporating the fertilizer into the ground will help speed up this process some.

However, when microbes are not active due to cold, saturated or compacted soils or low pH, the release of nutrients is greatly inhibited. Even under ideal conditions, it may take days to weeks for fast releasing nutrients to become available.

This process may take years for slow releasing nutrient sources. Therefore, a good dose of patience is needed while the all-important biology of the soil does its thing by breaking down, releasing and recycling essential nutrients to the soil and thus ultimately to the plants.

Note: Our Sustainable City is a recurring column in the Sentry intended to provide residents with news and information about sustainability initiatives in South Portland. Follow the Sustainability Office on Instagram and Facebook @soposustainability.

Jesse O’Brien is chair and agronomist of the Landcare Management
Advisory Committee.

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