Soil Testing for Lawns

If you are testing an existing lawn, don’t worry too much about the pH of your soil.

pH stands for “percent hydrogen,” and doesn’t tell you much except for how many hydrogen atoms are stuck to the soil. pH fluctuates by the day or hour, and with moisture, dryness, or how or when you took your sample. Hydrogen is not a nutrient to plants and your goal is to adjust nutrients, not hydrogen. 

Look beyond pH: If your grass has access to nutrients and healthy soil biology, the pH of your soil can be outside of the recommended ranges and still thrive.

Changing pH levels with fertilizers or pesticides can cause wild swings in important nutrients and kill the microorganisms needed to cycle nitrogen, phosphorus, calcium, and so on. Focus instead on building soil full of organic material and the microorganisms that cycle nutrients the grass needs. Ignore your pH reading for now and know that it will change with organic lawn care practices, or even after the next rain. 

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 out other important nutrients, and they are mined, non-renewable resources.

Balanced soil has between 65-80% Calcium (Ca) and 10-13% Magnesium (Mn), which are both salts.

If your Magnesium is a lot higher than 10-13%, and/or your Calcium a lot lower than 70-80%, soils can become very compacted and grass may not thrive. 

How to adjust calcium and magnesium levels:

• If your calcium/magnesium ratio is not far off from the amounts above, and your soil doesn’t seem compacted (i.e. you can push in a screwdriver easily), just focus on adding organic amendments like compost, so that the microbes can extract the nutrients the grass needs.
• If your lawn is compacted and has high magnesium, consider aerating your lawn and adding a small amount of oyster shell powder or wood ash, which are renewable resources of Calcium (instead of gypsum, which is mined.) This will reduce compaction, allowing for microorganisms to thrive, and open up pores for water to soak in to the root zone. 

Phosphorus(P) is a key nutrient for turfgrass to grow strong roots, transmit energy between cells, and strengthen cell DNA. While your grass relies heavily on phosphorus, it cannot get it directly from soil -- your grass requires the help of mycorrhizal fungi to process phosphorus. 

The Maryland Fertilizer Law and phosphorus

Phosphorus runoff negatively impacts the waters of the Chesapeake Bay by causing algae blooms, and   Maryland bans the application of phosphorous to lawns unless   a soil test within the previous 3 years shows it to be in the low to medium range   in this table.

How to increase phosphorus:

• Leave grass clippings and leaves on your lawn. Plant matter has plenty of phosphorus. 
• You also need the natural fungi in the soil to process the phosphorus and make it available to plants. A well-aged plant compost can be used as a top dressing at ¼ to ½ inch thick (and/or during aerating or reseeding,) or you can add seaweed, non-GMO alfalfa or soy meal, or wood ash as sources of phosphorus.
• Boost fungi in the soil by applying endomycorrhizal fungi purchased commercially, or through the use of composts and compost tea.

Soil tests won't measure for nitrogen, but the lab might suggest you add it.  We recommend you do not add nitrogen per directions on your soil test, because their results may be based off of the assumption that you are practicing non-organic lawn care. 

How to ensure enough nitrogen is in your soil:

Focus on cycling nitrogen in your lawn by:

• Letting grass grow higher (cutting it above 3 inches tall)
• Leaving behind all lawn clippings
• Incorporating clover and microclover into your lawn
• Aerating
• Adding organic amendments (worm castings, compost, compost tea, humus, chopped leaves, moldy hay, or azospirillum bacteria, etc)

If you are transitioning a lawn from synthetic to organic, you may need to continue to give it small amounts of additional organic nitrogen for a few years. Organic nitrogen sources include compost, worm castings, moldy haw or straw, coffee grinds, leaf clippings, or non-GMO soy, corn, or alfalfa meal.

Don’t worry about the organic matter content measurement on a soil test, especially since you might have accidentally added topsoil or roots to your soil sample. Every lawn can use more organic matter and microbial life to soak up water and provide optimal grass growth— in fact, you can never add too much in a lifetime!

Microbes, fungi, protozoa, and nematodes in the soil store nutrients, but also process and transmit them to plant roots in forms the plants need.

Adding organic matter:

• Sources of organic material and microbial life include moldy hay, seaweed, worm castings and worm compost tea, coffee grinds, sawdust, GMO-free corn gluten meal, bokashi compost tea, humic acids, shredded leaves, and some well-aged plant composts.
• Your lawn soils also need mycorrhizal fungi to help transport and extract nutrients, and store water. Apply endomycorrhizal fungi purchased commercially, or through the use of composts and compost tea. A constant focus on building organic matter and soil biology is a foundation for a healthy lawn.