What Does Phosphorus do for Grass?

By Brian Mounts | Feb 29, 2020
What Does Phosphorus do for Grass

Whether you’re trying to build a new lawn or overseed an existing one, you will certainly need phosphorus. Your grass just can’t take root without it. It is one of the most integral nutrients essential for root growth and development.

However, the crux of the matter is often adding it in the right proportion. This is because an excess of it can lead to pollution of water bodies. In this article, I’ll be showing you the essentials of phosphorus, its benefits, and how to apply it effectively.

What Is Phosphorus

Phosphorus (P) is the 15th chemical element in the periodic table. More than that, it is one of the three primary elements plants need for survival. The others are Nitrogen (N) and Potassium (K) As a matter of fact, all fertilizer packs have the symbols of these elements boldly written like this, N-P-K.

See these posts for more on what nitrogen and potassium do for grasses.

The percentage composition of Phosphorus in the soil determines how well your lawn will grow. Its deficiency can be quite disastrous. Your grass may not be able to survive the slightest form of erosion. Heavy rainfall will wash it away from the ground since the roots are weak.

What Are the Benefits of Phosphorus to Grass

Phosphorus is beneficial to grass in the following ways:

#1. It Enhances Grass Energy Reactions

Phosphorus plays an integral role that facilitates several chemical reactions within the grass. These reactions include ATP (Adenosine triphosphate) and ADP (adenosine diphosphate). They are paramount for the overall well-being of your grass.

#2. It Helps To Transfer Genetic Materials in Grass

Phosphorus is one of the essential components for the formation of DNA. As such, it is essential for plant development. It helps plants to transfer prevalent traits from one generation to another.

#3. Transfer of Sugar and Carbohydrates within Grass

You can liken phosphorus to be a mobility agent. Through photosynthesis, sugars and carbohydrates are generated. The ensuing energy that is generated is stored as ATP and transferred within the plant phosphorus.

#4. It Helps In Growth of the Grass Roots

Phosphorus is also one of the essential nutrients for healthy roots. Healthy roots also lead to health leaves and an overall rich look of your lawn.

In fact we have a full article dedicated to the development of strong roots in grass here if you are interested.

How to tell if a Lawn has a Phosphorus Deficiency

Before I overseed my lawn or fertilize, I often pay close attention to the blades of the grass, its appearance and other factors in determining if the lawn is lacking this vital nutrient or not. These are some of the tips to ascertain if your lawn lacks phosphorus:

#1. Reduced Leaf Surface Area

One of the symptoms of phosphorus deficiency is a reduced surface area of the grass. It would seem as though the grass is getting “thin” or shrinking inside. Just imagine it to be a 200lbs man that just lose 40lbs. You can agree with me that there will be changes in his body size. Although there is no loss of weight in the case of your lawn, the effect is just similar.

#2. Reduced Number of Blades

Lack of phosphorus won’t just reduce the surface area of the grass; it will also reduce the number of blades stemming out from each grass. Your lawn will look pretty scanty as though it’s beginning to have a taste of what other plants experience in the fall. The only difference is that in this case, your lawn isn’t shedding off its leaves. Rather, it’s not growing enough new ones.

#3. Stunted Roots

This is probably one of the most significant symptoms of phosphorus deficiency. If you’re observant enough, you will notice that the roots of the grass are no longer as deep as they used to. If you make a little effort to pull out a grass, it will uproot easily.

The poor roots are what accounts for some of the other symptoms like a reduced number of blades. This is because the low root mass won’t be sufficient to take up nutrients and water to the leaves. As such, other growth issues will set in.

#4. Dark Green Leaf Color

When there is a deficiency of phosphorus, it won’t be long before your grass accumulates carbohydrates through photosynthesis. This will lead to foliar deficiency, evident as a dark green color of the leaves as opposed to bright green color. At times, the entire grass affected will have this color, while in other instances, it will only be pigmented in some of the leaves.

#5. Reddish Purple Pigments on the Grass

Deficiency of phosphorus can also lead to a buildup of sugar in the grass. The resultant effect is the formation of what is known as anthocyanin pigments. Although anthocyanin pigments occur in some plants as red, blue or purple, it is commonly a reddish-purple color in the grass.

#6. Soil Test

I know I’ve listed a host of ways to spot a phosphorus-deficient grass. Nonetheless, running a soil test remains the most trusted and reliable way to determine the dominant and missing nutrients in your soil.

Experts choose this over other tips because phosphorus deficiency can be somewhat difficult to spot. Some of the symptoms listed here are similar to the deficiency of other nutrients, which can be pretty misleading.

More so, a soil test will give you the exact proportion of nutrients your grass is lacking. It will spare you the side effects of applying an excessive quantity of phosphorus and other nutrients.

Tips on How to Apply Phosphorus Correctly

Most of the side effects lawn owners experience with phosphorus is mainly as a result of wrong application of fertilizers. A lot of folks get this very wrong, and I wouldn’t want you to do the same. Just follow these timeless tips, and you’ll be good to go.

#1. Don’t Apply Fertilizers without Soil Test

I know you might have been tempted to do that. I also know it often pays off. But then, there is a danger of under-application and over-application of phosphorus and other nutrients. You can never be 100% sure of what your lawn needs by just observing the symptoms. Run a soil test at least once a year before the first fertilizer application.

#2. Don’t Apply Fertilizers on Dormant, Drought-Stricken or Frozen Lawn

Fertilizers need moisture to thrive. If you apply your fertilizers on any of types of lawns, the phosphorus and other nutrients will most likely runoff.

You should see this article for more on fertilizing your lawn in the spring.

#3. Ensure You Don’t Apply Fertilizers on Hardscapes

Your fertilizers should be restricted to the lawn and not on hardscapes such as driveways, and sidewalks. These places are not just hard, but also have a low moisture content that can absorb the nutrients. When the rain eventually comes, it will wash away the nutrients, which will lead to pollution of water bodies.

If you’re using granular fertilizers, plan the spread properly, so it doesn’t fall on these surfaces. At best, a drop spreader is more advisable than a spinner spreader. Even if the granules fall on the wrong surface, sweep them back into the lawn.

#4. Don’t Apply Fertilizers Just Before a Heavy Rainfall

Most fertilizers are available as either slow-release of controlled. This means that the phosphorus and other nutrients are not absorbed into the soil immediately after application. Heavy rainfall is potent enough to wash away these nutrients as soon as you apply them.

In this case, studying the weather is quite advisable. The same effect is bound to occur if the soil is saturated with water before application. It’s a no-no situation.

#5. Ensure the PH Level of the Soil Is Between 6.2 – 7.5

Again, soil PH is another important thing to look out for. You can easily tell this by running a soil test. Phosphorus thrives better at a PH ranges on 6.2 to 7.5. Anything outside of this range may deplete the availability of phosphorus in your lawn.

What Is the Best Time to Apply Phosphorus

Spring and fall are the best time to apply phosphorus. However, there is a debate between which of the two seasons is ideal for phosphorus application. Spring is characterized by heavy rainfall which may wash-off the fertilizers if not applied properly.

On the other hand, it is noteworthy that phosphorus has slow mobility. It takes more time for grass to absorb it compared to some other nutrients. This could have been a challenge, but various research has shown that the slow mobility of phosphorus makes its uptake time almost indifferent across the different seasons.

Nonetheless, spring is the best season for feeding plants. So it’ll be appropriate you introduce your phosphorus into the soil just the same time you’re applying other nutrients.


If your lawn must be as rich as you want it to be, then it’s got to get as much phosphorus as it needs. Its numerous benefits make it priceless. Nonetheless, you’ve got to be careful to apply just the right proportion.

You can learn even more about tending to the healthiest lawn possible right here on my dedicated grass growing guide. Check it out!