What is Fertilizer?
What is fertilizer? Fertilizer is any material, natural or synthetic, that adds nutrients to the soil. The primary nutrients of fertilizer are nitrogen (N), potassium (P), and phosphorus (K), or NPK for short.
What is Fertilizer Made Of?
Nitrogen
Think of nitrogen as the “up” part of fertilizer. In other words, it aids in keeping what is above the ground healthy. It helps keep the grass green, encourages growth and thickness of the grass. For plants, nitrogen is essential in keeping the leaves, fruits, and stems thriving.
Not Enough Nitrogen
Nitrogen moves freely in the soil. It is lost through rainwater, making it the macronutrient that requires more replacement than potassium and phosphorus. Without enough nitrogen, grass and plants will turn yellow and be thinner in density. This thinness in grasses allows weeds to grow.
If a plant lacks nitrogen, it can not produce amino acids. These amino acids help make proteins that plant cells need.
Too Much Nitrogen
You don’t want to add too much nitrogen, either. Suppose your lawn has an excess amount of nitrogen; the lawn’s ability to hold up to traffic, droughts, and high temperatures decreases.
Too much nitrogen in garden plants causes the plant to focus its energy on leaf production and not fruit production. This excess also results in a stunted root system since all the energy goes to the leaves.
Because nitrogen moves through the soil, an excess amount causes groundwater to become polluted.
Needing just the right amount of nitrogen is why a soil test is so important.
Phosphorus
Whereas nitrogen is the “up” part of fertilizer, phosphorus is the “down” part. It aids in creating a robust root system. It is essential to plant growth. Phosphorus also helps with photosynthesis, the movement of nutrients in the plant, and the ability for plants to use water efficiently.
Not Enough Phosphorus
If a plant does not have enough phosphorus, its stalk is thin and weak. Stunted growth and fewer leaves result from insufficient amounts of phosphorus. Because phosphorus aids in photosynthesis, sugars and starches accumulate in the plant, causing the dark-bluish leaves.
Too Much Phosphorus
Plants with excess phosphorus will eventually die due to the inability to take up necessary nutrients. Unlike nitrogen, phosphorus doesn’t move freely in the soil, meaning it doesn’t leach out of the ground with rainwater. Excess phosphorus can build up over time.
Potassium
Potassium is the part of fertilizer that helps the whole plant. It is the “all-around” part of the fertilizer. Potassium’s key role is to aid in gas exchange in the plant’s cells. With the appropriate amount of potassium, plants can better resist diseases and stressors such as excess moisture and temperatures.
Not Enough Potassium
Potassium moves through the roots and the leaves. When a plant does not have enough potassium, the leaves yellow around the edges, even becoming brown and scorched-looking. All parts of a plant (roots, leaves, fruit) suffer when potassium is unavailable. Without the appropriate amount of potassium, plants are more likely to fall victim to diseases.
Too Much Potassium
Too much potassium does not kill a plant. However, it does decrease the plant’s ability to take in other nutrients, such as nitrogen, magnesium, manganese, zinc, and iron. Plants show symptoms of nitrogen deficiency when potassium is low.
Potassium doesn’t leach as quickly from the soil. A lawn or garden needs very little potassium once established. Removing grass clippings from the yard reduces the amount of potassium available. It is best to leave the clippings on the lawn to maintain more adequate amounts of potassium.
The University of Tennessee Extension office created a nifty chart to help identify nutrient deficiencies in plants.
Numbers on the Fertilizer Bag
Every bag of fertilizer has three numbers listed. As the photo above illustrates, the percent nitrogen is the first number, the percent phosphorus the second, and the percent potassium the third. Filler makes up the rest of the bag.
Soil test results provide you with a recommended fertilizer ratio. For example, if you have more potassium in your soil, the Agriculture Extension will suggest a lower second number than the other two numbers.
The more complicated part of purchasing fertilizer is determining how much you need for your square footage. Bear with us; we are here to help you with this!
How to Calculate Amount of Fertilizer Needed
This part is a bit tedious and may feel like you are back in algebra class.
We had a soil test completed on our yard. Our results indicated we needed a fertilizer with the numbers 32-0-10. They also recommended we add 2-4 pounds of nitrogen per 1000 square feet of lawn. The industry standard is 1 pound per 1000 square feet. We needed to add a lot of nitrogen back into the soil.
The Calculations
How many pounds of the 32-0-10 fertilizer did we need for our yard size (2500 square feet)? Here is the formula to determine this:
2 lbs/1000 square feet ÷ .32 (32% nitrogen) = 6.25 lbs of nitrogen/1000 square feet
2500 square feet (our total square footage) ÷ 1000 square feet = 2.5
6.25 (lbs per 1000 square feet) x 2.5 = 15.63 lbs of 32% nitrogen needed to cover our yard
This video by Ewing is very helpful in walking you through the process!
I know we covered a lot of information. We hope you know the answer to “what is fertilizer?”
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What is Fertilizer?
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I have over 30 years of experience in the horticulture and landscaping field. Sharing my knowledge of all this plant-related is a passion of mine. I also enjoy spending time outdoors, whether hiking, canoeing, or sitting by a campfire.
Campfire momma says
Thanks for the formula. We were not putting enough fertilizer on our yard.
Jennifer says
Glad it helped!