Nutrient Management / Lawn Amendments

Nutrient management for grass cannot be done without also thinking about the biological life in the soil. Plants cannot access nutrients from the soil without the help of microbial life—bacteria, protozoa, nematodes, fungi, and other soil organisms. 

Maryland Fertilizer Law

The Maryland Fertilizer Law restricts the timing and the amount of phosphorus and nitrogen that can be applied to lawns. All of the recommendations below are for organic, renewable sources of nutrients.

Don't add synthetic fertilizers

Synthetic fertilizers are man-made, inorganic sources of nutrients. They are often by-products derived from the petroleum industry.

  • Synthetic fertilizers can easily leach out of the soil or wash off in a rain, heading directly to ground and surface waters, killing off aquatic life and creating dead zones. 
  • Production of synthetic fertilizers requires burning of fossil fuels, mining, and creates many toxic byproducts. For example, to make 150 large bags of lawn fertilizer, it takes as much natural gas as it would to heat the average home in Montgomery County for half a year.
  • Plants fertilized with synthetic fertilizers often have weaker growth and are more disease prone.
  • Most important, though, is that synthetic fertilizers can be highly toxic to your soils. Learn more about the impacts of synthetic fertilizers on soil ecosystems.  
Soil. Image by sanddebeautheil, 123RF
Image by sanddebeautheil, 123RF

If you must use a manufactured fertilizer, look for the “OMRI” label

The Organic Materials Review Institute (OMRI) certifies products and materials for organic use, and many organic gardeners rely on these products for pest control. But if you follow our other lawn care tips , or target specific problems we list below, you may never need an OMRI listed product.  

Common nutrients and other lawn amendments


While it is not a nutrient, conventional lawn guides often tell you to adjust your pH. But pH only measures hydrogen atoms in the soil, which plants won’t use.

If your grass has access to nutrients and healthy microorganisms, the pH of your soil can be outside of the recommended ranges and still thrive. Ignore your pH reading for now and know that it will change with organic lawn care practices, or even after the next rain. 

Changing pH levels with fertilizers or pesticides can cause wild swings in important nutrients and kill the microorganisms needed to cycle plant nutrients like nitrogen, phosphorus, calcium, and so on.

If your pH is below 5.6 or above 7.6  AND you struggle with getting grass to grow:  
If your pH is on the far end of the scale, and you struggle just to get grass to grow in an otherwise ideal location, you may want to adjust your pH along with other organic amendments.

  • If your pH is below 5.6, and you have weeds or moss invading your lawn: Add wood ash or wood ash tea to raise the pH to a more desirable level.
  • If your pH is above 7.6, and you have weeds invading your lawn:  Apply compost or pine needle mulches to slowly lower the pH.
  • Avoid lime, gypsum, or sulfur, as they can be toxic to microorganisms, leach important nutrients if added to soil, and they are mined, non-renewable resources.


Carbon is not actually a nutrient, but is one of the key elements of organic materials and healthy soil that helps hold nutrients. Carbon also prevents soil compaction, stores moisture, and provides habitat for microorganisms. 

Carbon is released into the soil when plant roots and stems die, and when roots exude liquid carbon. Humus, which is highly digested organic material that is no longer food for most organisms, is one of the best sources of carbon for soils, but can take years to accumulate.   

Adding carbon sources to your lawn helps improve soil, while adding microorganisms or aerating your soil will help move carbon down into the soil.

Sources of carbon:
  • Grass clippings and leaves
  • Compost
  • Dry seaweed
  • Humic acids (Seaweed extract and humic acids added together will also stimulate the growth of mycorrhizal fungi. Humic acids are also high in worm castings.)
  • Sawdust, aged wood chips, or newspaper (best if composted first)
  • Straw
  • Blackstrap molasses
Straw. Photo by nito500,123RFStraw is a great source of carbon. Photo by nito500,123RF


Nitrogen is important for plants to make chlorophyll, proteins, amino acids and hormones. The main way nitrogen is made available to plants is through fixation by microorganisms. 

It is not enough just to add nitrogen to the soil, you also need to have healthy soil biology and microorganisms. Nitrogen is the most abundant gas in our atmosphere, at 78% of the air. But it is only made available to plants via two natural processes: lightning, or fixation by bacteria.

Sources of nitrogen:
  • Grass clippings return between 50-100% of the nitrogen needed by plants. Leaves also return a hefty amount of nitrogen.
  • Compost provides an abundant source of nitrogen and associated bacteria to extract it for plants.
  • Non-GMO corn gluten, soybean meal, or alfalfa meal.
  • Seaweed and coffee grounds.
  • Earthworm castings.
Grass clippings. Photo by Jesus Jauregui, 123RFGrass clippings are a great source of carbon and nitrogen. Photo by Jesus Jauregui, 123RF
Nitrogen fixing microorganisms and plants:
  • Clover plants contain bacteria that fix excess nitrogen from the atmosphere and can be seeded into a lawn.
  • The interaction between nematodes and bacterium provides 30-50% of the nitrogen needed for grass roots, and can be increased through compost and compost tea.
  • Azospirillum are nitrogen fixing bacteria that provide up to 30% of the nitrogen needed for grass roots and can be increased through some biostimulant products.

Extra nitrogen may be needed when transitioning from chemical based practices, or if you want to brighten up a lawn in early spring, or if the lawn shows nitrogen deficiency (leaves are light green or yellow during peak growing season). Synthetic nitrogen will give grass a temporary “green boost,” but will harm the grass and soil in the long term, and should be reduced and removed from lawns within a year of transition.

The Maryland Fertilizer Law and Nitrogen

  • A single nitrogen application must not exceed .9 pounds per 1,000 square feet, or .7 pounds soluble nitrogen per 1,000 square feet.
  • No nitrogen may be applied between November 15 and March 1, with the exception of water soluble nitrogen, which may be applied by licensed professionals at a maximum rate of .5 pounds per 1,000 square feet between Nov 16 and December 1.
  • Learn more about the Maryland Fertilizer Law.


Phosphorus (P) is important for plants to generate energy and it improves growth. Nearly all our soils have phosphorus that weathered from the parent rocks, but microorganisms are critical to making phosphorus available to plants. Most critical are mycorrhizal fungi, which convert phosphorus into forms that plant roots can absorb.

Sources of natural phosphorus:
  • Help your lawn absorb the phosphorus that naturally occurs in your soil.  Add and encourage the growth of endomycorrhizal fungi with compost and compost tea. Compost can also be a source of phosphorus. 
  • Grass clippings return 1.8 pounds of phosphorus per 1,000 square feet within one year. Leaves also supply a hefty amount of phosphorus.

Maryland Fertilizer Law and Phosphorus:

In order to apply materials with phosphorus, a soil test within the previous 36 months must show it to be in the low to medium range in this table .
  • A single phosphorus application must not exceed .25 pounds of phosphorus per 1,000 square feet, with an annual maximum of .5 pounds per 1,000 square feet.
  • No fertilizer may be applied between November 15 and March 1.
  • Learn more about the Maryland Fertilizer Law. 



Potassium (K)  is important for overall grass health, helping it become drought and cold resistant, resist pests, and grow faster. Potassium is usually found in high amounts in the soil, but it is bound in insoluble forms in mineral soils, which can only be extracted by microorganisms, fungi, and slow weathering from the soil.

Proper aeration of soils is critical for potassium uptake by plant roots, as are bacteria and fungi that can convert potassium to a form that roots can absorb.


Sources of natural potassium:
  • Help your lawn absorb the potassium that naturally occurs in your soil.  Add and encourage the growth of bacteria and fungi with compost, particularly compost made from fruits, vegetables, and banana peels.
  • Kelp meal and seaweed are great sources of potassium, while also supplying micronutrients.
  • Wood ash supplies potassium and micronutrients—just be cautious using it if your pH is already high, as it raises pH.
Dried kelp by yingtustock123, 123RF
Dried kelp is a great source of potassium. Photo by yingtustock123, 123RF



Micronutrients are nutrients important to plant health that occur in smaller amounts in the soil and/or are not as critical as the other nutrients/chemicals mentioned above. They are important for strong, pest-resistent plants. 

An occasional boost of micronutrients can help rejuvenate your grass, particularly after a stressful time, such as extreme weather, heavy trampling, or exposure to a chemical. 

Sources of micronutrients:

  • Wood ash tea (made like compost tea but without aeration) can supply small amounts of molybdenum, manganese, copper, boron, zinc, and iron.
  • Sea minerals contain all the elements on the periodic chart, including 76 minerals. Be careful choosing products to ensure they are low in salts and formulated for lawns.
  • Black-strap molasses contains trace elements including calcium, magnesium, manganese, potassium, copper, iron, phosphorous, chromium, and cobalt, and boosts soil bacteria. 
  • Compost micronutrients vary, depending on what was put in the compost pile.
    • Manganese: Carrots or tomatoes
    • Boron: Apple cores and banana peels
    • Copper: Mushrooms and potatoes
    • Iron: Spinach and lentils
    • Calcium: Dried eggshells
    • Zinc: Pumpkin or squash seeds
Microorganisms in soil by drik 123RFWhile you can only see microorganisms with a microscope, they are extremely important to the health of your soil!    Photo by drik 123RF

Beneficial Microorganisms

For plants to obtain nutrients, they need more than just sun, oxygen, and water; they also need microorganisms to turn nutrients into forms they can absorb through their roots. A healthy population of organisms will also provide defense and attack against disease causing organisms that harm grass. 

In a teaspoon of healthy soil, there can be over a billion bacteria, fungi, protozoa, actinomycetes, and nematodes. Poor soils often need a boost to increase their populations.

Sources of microorganisms:
  • Compost, earthworm castings, and compost tea are full of life, especially bacteria, fungi, actinomycetes, and protozoa.
  • Effective Microorganisms (EM) can be purchased in liquid form, and provide bacteria in large amounts.
  • Endomycorrhizal fungi can be purchased to boost important soil fungi that capture and convert phosphorus.
  • Azospirillum bacteria can be purchased to boost nitrogen fixation for grass plants.
  • Beneficial nematodes can be purchased to attack and consume eggs and larvae of insect pests.
  • Earthworms, spiders, and other soil invertebrates can be imported into lawns from compost, or with a handful a healthy garden or forest soil from adjacent areas.

You may have noticed, but we have not suggested products that are derived from animals or require mining. We recommend only using those products if plant-based amendments are not available.