Decoding Your Soil Test

Soil tests provide valuable information about what challenges and advantages your lawn has. But, without the right know how (years of school and piles of books) a soil test can feel like a nonsensical jumble of numbers. That's why we did all the complex decoding stuff for you.

Minimal Levels of Sustainable Nutrition

At Sunday, we practice what’s called “Minimal Levels of Sustainable Nutrition”. This means we provide only what your lawn actually needs.  This keeps your soil in shape, so it doesn’t become lazy and reliant on inputs. It’s also a more economic and environmental method that prevents waste or run off.

 

*The numbers we share below are interpretive values. Ranges vary for specific conditions. If your lawn looks good, you’re good.

The Dirt on Your Soil

The following sections will help you decode common abbreviations seen on soil test results. Then we dig into what each nutrient’s job is and how much you need to have a healthy lawn.

 

OM – Organic Matter is the amount of materials derived from organisms in your soil. OM eventually breaks down into nutrients and gets absorbed by your grass and plays a critical role in the soil’s ecosystem. We like to see OM at a minimum of 2%; even higher for sandy soils.

 

CEC – Cation Exchange Capacity Simply put, this is the soil’s ability to retain water and nutrients. Lower CEC means the soil is less able to hold nutrients and vice versa. CEC is very difficult to change, however, you can change your lawn care regimen to fit your soil’s CEC. 4-20 is a good range for lawns. While not an exact science, you can estimate soil’s texture from CEC:

-0-10: Sandy
-10-20: Silty
->20: Clay

 

pH – pH impacts how easily grass can absorb certain nutrients. A perfect pH falls between 6.5-7.0; however, grass can easily tolerate anything between 4.0 – 9.0. Pursuing a perfect pH is usually unnecessary, expensive, and can take years.

 

Sol Salts – Soluble Salts indicate the risk of fertilizer burn and pet spots; the higher the number, the greater the risk. Salts make it harder for grass to absorb water, and this can be exacerbated if fertilizer is applied on dehydrated grass in dry soil. There’s little to worry about when soluble salts are below 0.7. Above 3 can start to cause serious problems, depending on grass type.

 

Estimated Nitrogen Release is how much free nitrogen your lawn could get from OM. The actual amount of nitrogen release is influenced by weather, microbiome health, and use of lawn, so emphasis on estimated.

Macronutrients

P – Phosphorus is a key macronutrient involved in many cellular processes. It tends to be more important for newly installed lawns. Also, a major pollutant, apply with caution. Only one of our nutrient blends contains Phosphorus. 21 ppm is all the Phosphorus an established lawn needs.

 

K – Potassium is another macronutrient that is vital to grass’ ability to endure stress, however, it is often over-applied. Too much potassium increases the risk of certain diseases. Many of our nutrient blends contain a small amount of potassium. This helps your lawn maintain healthy levels. 37 ppm is adequate for lawns.

 

Nitrogen – N is the most important nutrient for lawns. Unfortunately you can’t tell true nitrogen levels from a soil test because it fluctuates quickly and constantly. By the time your soil sample reaches the lab, your soil at home will likely be radically different. Some microbes consume nitrogen, others create nitrogen, and it’s common for nitrogen to volatilize back into the atmosphere.

Secondary Macronutrients

Ca – Calcium is crucial for frost-hardy plants, but is abundant in 99% of US soils. It’s very important, but your soil probably has enough already (only 37 ppm is needed.). Calcium can be helpful if trying to raise pH.

 

Mg – Magnesium is a critical nutrient for chlorophyll to function. 47 ppm is enough for grass, and only 1 out of 100 lawns have a magnesium deficiency.

 

S – Sulfur creates beneficial amino acids and aids in new growth. 7 ppm is all your lawn needs, however, higher levels can be helpful in preventing certain diseases. Excessive sulfur can cause problems in lawns that get easily waterlogged.

Micronutrients

Fe – Iron Grass loves iron; weeds and diseases not so much. Iron will also give grass a darker, deeper color. Below 75 ppm is considered deficient. We like to see levels around 310 ppm, but we’ll probably send you a little iron anyways to help prevent weeds and diseases.

 

B – Boron is the most micro of the micronutrients, as your lawn only needs 0.4 ppm max. Yet, about 15% of the lawns we see are short on Boron. It plays many roles, notably in building sugars. Use caution when adding Boron, as going over 5 ppm can cause major problems.

 

Mn – Manganese Not to be confused with magnesium, manganese is needed for photosynthesis to work and is more sensitive to pH than other nutrients. About 5 ppm is sufficient across normal pH levels, and only about 2% of lawns have a deficiency.

 

Cu – Copper is important for photosynthesis and some proteins. 0.3-1 ppm is all you need. Given how expensive copper is, deficiencies should be addressed with compost as opposed to copper fertilizers.

 

Zn – Zinc is an important ingredient for most enzymes. Your lawn needs only 0.5 -1 ppm, and deficiencies are rare on most American lawns.