Organic Lawn Fertilization

Grass Root structure The current “green movement”, with its interest in organic, sustainable gardening, has grown to include a variety of lawn care practices, including use of organic fertilizers derived from natural sources such as plant or animal wastes. Examples of organic fertilizers include biosolids (e.g., Milorganite) and manure-based fertilizers. As use of organic fertilizers becomes more widespread, understanding ways in which they differ from conventional, inorganic fertilizers is important.

Difference Between Organic and Conventional Fertilizers

One pound of nitrogen (N) from an organic fertilizer almost never produces the same result as one pound of N from a conventional fertilizer. Organic fertilizers tend to contain complex N-containing compounds that must be broken down by soil microorganisms before the N can be used by plants. This process occurs slowly over a long period of time and the microorganisms use a substantial portion of the N for their own growth.

Fertilizing lawn with drop spreader In general, in order to get the same result from an organic fertilizer as a conventional fertilizer, one needs to apply approximately twice as much organic fertilizer. After roughly 10 to 20 years of fertilization with an organic product, organic nitrogen will accumulate in the soil to the point that grass will begin to require less fertilization.

Another major difference between organic and conventional fertilizers is that organic fertilizers usually do not cause grass to green up as fast as conventional fertilizers do. Greening is related to the amount of soluble N available to the grass. Typically, conventional fertilizers have higher amounts of soluble N than organic fertilizers.

Some organic fertilizers contain no soluble N at all, while others may have up to 50% of their N in a soluble form. Since the insoluble portion of N in organic fertilizers becomes available through the action of microorganisms, N release in organic fertilizers is slower, especially in spring and fall when soils are cooler and microorganisms are less active.

First, Do A Soil Test

The first step in going the organic route with an existing lawn is beefing up weakened soil, which means starting with a soil test. That way you'll know which nutrients are lacking and which organic amendments you'll need to incorporate. For example, soil with a calcium deficiency can be top-dressed with gypsum; and soil low in magnesium might need a healthy dose of the mineral langbeinite.

You will need to dig up samples from several different areas of your lawn (2 cups of soil total), and mail them off to a lab to be analyzed. Call local nurseries and university extension offices to see if they offer soil tests (both should provide soil-sample boxes).

Once you know which amendments you need, you should prepare the lawn by mowing the grass down to about 2 inches, pulling up weeds, removing thatch (dead grass and roots that accumulate on the surface), and aerating (a power aerator that pulls up plugs of soil can be found at most rental yards). This will enable your soil to fully absorb any amendments you add.

Start Composting

Compost Bin Whatever the test results, you'll also want to spread a half-inch of compost on the lawn to add essential organic matter to the soil. It's almost like a blood transfusion. It improves soil structure—especially in clay or sand-heavy soil—and is full of beneficial organisms, including bacteria, algae, fungi, and nematodes, that keep your soil healthy.

Look for compost that is made up of decomposed organic plant material, similar to the stuff you find on the forest floor. You can buy it at nurseries, or collect your own yard waste in a backyard bin. Many municipalities have composting programs, which provide information on how to compost and, sometimes, discounted composting bins. It is also recommended speeding up your lawn's transition to organic by brewing your own compost tea and spraying it on your lawn once a month with a backpack sprayer or a watering can.

How should I fertilize my lawn when using an organic fertilizer?

Make an initial application of an organic fertilizer to your lawn in late May or early June (i.e., around Memorial Day). Application of a slow-release fertilizer at that time will gradually produce N that can be used by grass all summer long. Consider a second application of an organic fertilizer at the beginning of July (i.e., around Independence Day), but only if your grass is still green and not under drought stress.

Make a final application in early fall (i.e., around Labor Day). This final application will help promote faster greening and faster growth the following spring. If you leave clippings on your lawn as you mow, N will be released as the clippings decompose providing the equivalent of one additional fertilizer application of N during the year.

In general, when using an organic fertilizer, keep the following points in mind:

  Applying an organic fertilizer at the labeled rate will not green your lawn in the same way you have come to expect from using conventional fertilizers. A similar greening can be achieved by applying an organic fertilizer at twice the labeled rate. In addition to supplying nitrogen, an organic fertilizer will add more organic carbon to the soil, which may improve soil structure and soil biological activity over the long term, and allow you to reduce your fertilization after 10 to 20 years.

  Use an organic fertilizer that contains some soluble N. This will lead to quicker greening and will likely lead to more efficient use of N. Using a product with soluble N is especially important for applications made in the spring and fall. The soluble N content is listed on the label of every bag of fertilizer.

  Most organic fertilizers contain phosphorus and have the potential to contaminate surface and ground water if used improperly,even though they are exempt from state restrictions on the use of phosphorus-containing fertilizers. Always sweep fertilizer off of solid surfaces (e.g., driveways and sidewalks), and avoid application directly into bodies of water or on frozen soils.

Care and Maintenance Tips

Watering Lawn When it comes to mowing a naturally grown lawn, conventional wisdom still applies. Cut it too short and it doesn't develop the strong, healthy roots it needs to fend off weeds and disease. So find out the best height for the type of turf you're growing.

Cool-season grasses, such as Kentucky bluegrass and red fescue, prefer to be between 3 to 4 inches high; while warm-season varieties like Bermuda grass can be maintained at 1 to 1 1/2 inches. Be sure to mow with a mulching attachment or a mulching reel mower and leave the clippings where they fall; they're a natural source of nitrogen as they decompose.

When it comes to conserving water, the good news is that organically-cared-for lawns require less water than chemically treated ones, since the latter needs lots of moisture just to digest all the synthetic fertilizers and pesticides fed to them.

As with any lawn, the key is to water infrequently and deeply, encouraging turf to send down deep roots and making it less susceptible to drought and disease. The best time to water is early morning, since it gives your lawn plenty of time to absorb it and dry off in the sun.

Most lawns require about 1 to 2 inches of water per week in summer. Use a rain gauge to measure how much water your lawn's getting; and make sure your sprinkler water isn't being wasted on your driveway or street.

Further Information

 The Life Cycle of Plants: Fertilization
 The Spruce: How to Make Your Own Fertilizer
 Pollination and Fertilization
 4 Ways To Use Eggshells For Your Plants
 10 Ways to Use Banana Peels in Your Garden

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