Healthy grass starts at the root. This is where your grass pulls all the nutrients it needs to grow green, lush and resilient. A lack of any one nutrient can cause a sequence of events that may lead to stunted growth, thinning grass, large brown patches, or a disease that can take over your entire lawn.
Understanding the critical nutrients in your soil and how they affect your grass is key to keeping a healthy lawn.
Our easy guide to the nutrients in your soil is a great place to start gaining the knowledge you need to keep a lush, green yard your neighbors will envy.
Nitrogen is one of the key elements of life, including plants. Unlike many nutrients your grass absorbs from the ground, nitrogen does not originate there. It is actually in the air surrounding the plants and is brought into the ground via rain, soil organisms, and, of course, fertilizer.
How do you know if you have a nitrogen shortage? The tell-tale sign is a rapid color change in older, more established grass relative to newer grass. Nitrogen tends to drift to the newest growth, leaving the older grass to turn a lighter shade of green, yellow or, in some cases, pink and eventually die.
A shortage in nitrogen generally occurs in sandy soils, but it can also be subject to leaching from excess rainfall or overwatering.
Too much nitrogen in your soil can create havoc too, causing your grass to become diseased and weaken or rot.
If you think you have low nitrogen, the first step is a soil test to make sure. While you may notice the tell-tale signs of low nitrogen, this may not always mean you’re dealing with a nitrogen issue.
You can purchase soil testers online and in stores that will tell you whether your yellowing grass is a nitrogen issue or not. They can also recommend amendments to fix the deficiencies your soil has.
Once you’ve determined the issue is nitrogen and the testing company provided you with recommended amendments, simply apply a high-nitrogen fertilizer in the amount recommended by the test to rectify your issues
Phosphorus is one of the more interesting nutrients in the world of grass because it can both prevent and cause water pollution. It all depends on how you use it.
Before we dive into the specifics of proper use, let’s talk about what phosphorus does for grass. Phosphorus is critical in root health, and healthy roots promote nutrient absorption, a healthy shoot, and ultimately, a greener and healthier lawn.
A lawn lacking phosphorus will have a lower density, spring green-up may be slower than normal, and the leaves may turn purple, reddish-brown or unusually dark green.
As we said, phosphorus is a mixed bag in terms of pollution. Too much can result in runoff into waterways and promote excess algae, throwing the ecosystem into disarray. Too little can result in thinner grass coverage, which can result in more phosphorus runoff into waterways and have the same effect.
The key is balance.
If soil tests show your phosphorus is low, you will want to take certain precautions when adding fertilizer with phosphorous to avoid polluting the local waterways. On top of adding only the amount of phosphorus-containing fertilizer as the test recommends, the University of Vermont also recommends:
- Applying the fertilizer when the soil is dry or moderately moist and water it in
- Never applying it after a fresh rainfall, avoid overwatering
- Using a drop spreader for more precise placement
- Avoiding mowing immediately after fertilizing
- Aerating your yard if it is subject to a lot of foot traffic to prevent runoff
If your grass starts yellowing in its older, more established leaves and dieback at the tips, there is a good chance your soil is lacking potassium.
Sometimes called “potash,” potassium is a macronutrient, which means your turf needs a significant amount of it relative to other nutrients to remain healthy.
Potassium plays several critical roles in your grass’ health, including building thicker cell walls that help it recover from daily stresses of foot traffic and mowing, but this also helps it avoid disease and withstand severe weather patterns. Potassium’s other key role is to help your grass absorb water and nutrients, and synthesize proteins and starches.
If you notice signs of low potassium, it is still key to verify the deficiency via soil testing before applying fertilizer. Too much potassium can negatively affect other nutrients like calcium, magnesium, and manganese.
Calcium is yet another key nutrient all plants need to thrive. For humans, calcium helps build strong bones and teeth, but for plants, it creates a barrier between the cells and any outside pathogens. This helps prevent diseases and pests from ravaging your lawn. Also, the right calcium levels help maintain its pH levels in your soil.
If your soil lacks calcium, you will likely notice root tips turning brown and dying, leavings browning and curling, and new leaves sticking together and tearing as they open.
If soil tests show a calcium deficiency, you can’t just dump a gallon of milk on your yard and call it a day. Instead, you need to apply calcium carbonate, which generally comes in the form of limestone. The soil test will tell you precisely how much lime to add to your lawn to restore its calcium levels.
Use care not to add too much, as this can cause deficiencies in magnesium, potassium, manganese, and iron.
An often overlooked micronutrient, magnesium can play a big role in your grass’ longevity. This is especially true in areas that deal with cold winters, as magnesium helps strengthen the turf ahead of the cooler months by supporting chlorophyll production and helping absorb and process other nutrients like nitrogen, phosphate and iron.
Magnesium-deficient lawns display distinct signs, including older leaves losing their color and turning from light green to cherry red while the veins remain green. Eventually, the leaves die off.
If soil tests reveal a magnesium shortage, you can apply a mixture of Epsom salt and water to your lawn to rectify the issue. Follow the amendment recommendations from the soil test carefully, as too much magnesium can create calcium, potassium, and manganese deficiencies.
The main purpose sulfur has in the lawn is to help lower a high soil pH.
High-pH or an overly alkaline soil affects the availability of many nutrients grasses need.
Sulfur deficiencies can be tricky, as the symptoms include pale-green and yellow leaves, which mimics a nitrogen deficiency. This is where tissue testing may be required to narrow down precisely what is causing the issue, as experts find minimal value in sulfur soil tests.
If testing shows sulfur deficiency is the issue, you will want to plan for a semi-long road ahead. Yes, you can purchase a sulfur-containing fertilizer and apply it just as recommended by the tissue test. Where time comes into play are the months to years it may take the bacteria in the soil to convert the sulfur to the sulfuric acid your grass can absorb.
Iron plays a key role in photosynthesis, and a lack of it can result in your grass turning yellow. Fortunately, there are warning signs that start long before it gets too serious. The initial tell-tale sign of an iron deficiency is interveinal chlorosis, which is the yellowing of the leaf between the veins in younger grass.
If left untreated, the yellowing will spread to the more established blades of grass and potentially result in your lawn dying off.
If a soil test shows your iron levels are off you can spray your lawn with an iron supplement for a short-term fix. To fix it long-term, you’ll need to use the information a soil test provides to fix the issue. Iron deficiencies generally stem from alkaline soil (pH 7 or higher), excess phosphorus or compacted soil.
Like iron, manganese is an essential micronutrient that plays a large role in photosynthesis. Grasses lacking manganese will show interveinal chlorosis, which is also why manganese deficiency is often mistaken for lack of iron.
These similarities make it even more important to test your soils to see where the issue lies, as you will treat them very differently. Unlike iron, you can apply a manganese-containing fertilizer to rectify the issue quickly.
Zinc is another micronutrient that plays a small but pivotal role in your grass’ health, as it helps in the uptake and processing of various proteins and enzymes. It also is a key part of growth hormone production.
Without the proper zinc levels in the soil, you’ll notice the same interveinal chlorosis noted in the manganese- and iron-deficient plants. Zinc deficiencies stand apart from these with stunted growth and rosette formation at the ends of the blades.
Zinc deficiency can come from various sources, including low zinc levels in the soil, high soil pH, low soil temperatures, high phosphorus levels, and more. This is why it’s critical to test your soil before adding amendments or making other changes.