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Gardening — Milorganite

Milorganite Package Milorganite is a fertilizer made in Milwaukee from treated sewage sludge. It is categorized as a natural fertilizer because 85 percent of its ingredients are organic, although the U.S. Department of Agriculture does not allow its use in certified organic agricultural production. It is not compost. The name 'Milorganite' is derived from the first syllable of these three words: Milwaukee, organic and nitrogen.

Both Milorganite and chemical fertilizers are designed to nourish your grass. Because grass is the largest plant in your yard, and the one that receives the largest abuse from weather, insects, drought and mold, it requires a great deal of maintenance. It also needs feeding more frequently. Unlike chemical fertilizers, it releases nutrients slowly, so it may be a better choice for preventing excess nutrients draining into waterways and groundwater.

Milorganite vs Chemical Fertilizers

Unlike chemical fertilizers, it releases nutrients slowly, so it may be a better choice for preventing excess nutrients draining into waterways and groundwater. Also, it's easy to over-fertilize with chemical fertilizers which can result in 'burned' grass. Since Milorganite is an organic fertilizer that contains low amounts of nitrogen it won't burn your grass, even if over-applied.


Fertilizer composition is listed in ratios of NPK -- nitrogen, phosphorus and potassium. Milorganite contains 5 percent nitrogen, 2 percent phosphorus and .32 percent potassium. It also contains the secondary nutrients calcium, 2.1 percent, sulfur, .58 percent and magnesium, .68 percent, as well as 4 percent iron. It has traces of other micronutrients, such as zinc, copper, boron and chloride.

Grass needs iron to make chlorophyll, necessary for photosynthesis. If the green chlorophyll does not develop in young grass, the leaves look yellowish-green and have yellow veins. This is called iron chlorosis.

How It Works

Graphic of man using a rotary spreader Milorganite is made up of 85 percent organic material. Organic materials release nutrients to plants over time, so are known as slow-release fertilizers. While over-application of chemical fertilizers can burn plants, organic ingredients won’t. Instead of a quick, chemical boost, microbes in the soil digest the nutrients in Milorganite and deliver them to plants over a period of two to three months. The nutrients stay in the soil until conditions are optimum for plants to take them up during the growing season.


It can be applied anytime during the growing season because it doesn’t contain anything that will burn grass. High temperatures, drought and rainfall do not prevent Milorganite application. It does not need to be watered in, although during the dry season, watering will push the material into the soil faster.


A high nitrogen count will cause your grass to become green such as in commerical fertilizers. This will result in not only greener grass, but it will also grow at an accelerated rate. This results in more frequent mowing. Milorganite contains a much lower amount of nitrogen but adds iron, which keeps the grass green but does not accelerate lawn growth. It is considered a slow-release fertilizer.


Milorganite is approved for home gardening use by the Environmental Protection Agency. Miloganite is not toxic to humans or pets. Because its source is wastewater, however, it may contain traces of pharmaceuticals. Because of Milorganite’s relatively high iron content, it is likely to cause stomach upset and vomiting if a handful or more is eaten. Store all fertilizers away from children and pets.

Further Information:

 Wisconsin Native Fruit Trees
 Wisconsin Native Berry Shrubs
 Lovely Native Violets
 Use Eggshells For Your Plants
 How to Use Banana Peels in Your Garden

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