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Fertilizing lawns

Quick facts

  • Fertilizers add nutrients like nitrogen, phosphorus and potassium to the soil to help plant growth.
  • On every bag of fertilizer, you will find an analysis of the nutrients in the fertilizer.
  • Natural and manufactured fertilizers have different characteristics.
  • All types of fertilizer can contribute to pollution, if used incorrectly.
  • Spot treating weeds may be more effective than using a weed-and-feed product over your entire lawn.

All fertilizers add nutrients to the soil to help plant growth. Natural and manufactured fertilizers have different qualities, but precautions must be taken when using either.

When properly applied, fertilizers pose few risks to humans or animals.

If used correctly, fertilizers can help you improve and maintain your lawn. Healthy lawns limit erosion, cool the environment and control allergens, among many other benefits.

See Environmental benefits of healthy lawns.

Why fertilize?

Fertilizers are important in lawn care because they supplement the soil with needed nutrients.

  • Grass plants need nutrients because of the many stresses people apply to them.
  • Grass uses nutrients to repair damage done by normal wear and mowing.
  • Other plants in the landscape, such as trees, flowers and weeds, also consume the nutrients.
  • Nutrients are lost when clippings are removed while mowing.

What is in fertilizer?

The three main nutrients needed by plants are nitrogen (N), phosphorus (P), and potassium (K).

  • For a home lawn, the most essential nutrient to add on a regular basis is nitrogen.
  • Phosphorus is present in high levels in many Midwestern soils.
    • Adding phosphorus in the form of fertilizer is usually not needed.
    • Established lawns show little response to added phosphorus.
    • Because phosphorus does not easily move in the soil, additional amounts are often beneficial when establishing new turf.
    • Only apply phosphorus if a soil test indicates a need.
  • Potassium may need to be supplemented.
    • Coarse-textured (sandy) soils often need added potassium.
    • Use a soil test to determine when to add potassium.

Plants also need many other nutrients, but in very small amounts. These are called micronutrients.

Concentration of nutrients

The label on a bag of fertilizer includes an analysis of the concentration of nutrients. Each number in the analysis represents a percentage of the total weight of the product that is the actual nutrient.

  • The first number indicates the amount of nitrogen, or N.
  • The second number is the amount of phosphorus in the form of phosphate, P2O5.
  • The third number is the amount of potassium in the form of potash, K2O.

For instance, a 10-10-10 is a balanced food with equal parts nitrogen, phosphorus and potassium.

High numbers of each nutrient in a particular fertilizer usually mean the type can be applied less often. This is similar to the differences between a concentrated laundry detergent and a more dilute one.

Natural organic fertilizers usually have a lower concentration of nutrients than manufactured types. As a result, more organic fertilizer is needed to supply the same amount of nutrients.

It’s important to consider nutrient amounts when figuring the cost since more bags of the low-analysis fertilizer will be needed to supply the same amount of nutrients.

A soil test from the University of Minnesota Soil Testing Lab can help you determine whether your lawn lacks essential nutrients or has too much.

Fertilizing basics

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Fertilizer FAQs

Are manufactured fertilizers going to burn the lawn?

  • "Burning" occurs when fertilizer is so concentrated around the roots that it essentially pulls water out of the plant.
  • Burning most commonly occurs when a lawn is fertilized in hot weather or without being watered.
  • This is particularly a problem with fast-release fertilizers.
  • Slow-release products, both natural or manufactured, also have the potential of burning, but the nutrients usually do not build up such high concentrations in the soil.
  • To prevent burning of the lawn, always water after applying any fertilizer, unless the label recommends otherwise.

Are manufactured fertilizers more likely to cause pollution?

All fertilizers must be broken down to the same nutrient form. All types of fertilizer can contribute to pollution, if used incorrectly.

  • The leaching of nitrates may be of concern in areas of sandy soils when over-watering and over-fertilization occur, particularly with the use of fast-release forms.
  • Excess phosphorus has also been involved in lake and stream pollution.
    • If the lawn is dense and vigorous, however, it contributes very little, if any, to runoff. The grass roots bind the soil tightly, promoting infiltration of water and nutrients.
  • Do not leave fertilizer and organic matter (lawn clippings, leaves) on sidewalks, driveways and gutters. These contribute substantially to nutrient runoff into lakes and streams.

See Water wisely.

Does fertilizer damage the soil and the creatures that live in it?

Some nitrogen fertilizers tend to reduce the pH of the soil and thatch slightly.

  • pH is a measure of acidity, with 7 being neutral, below 7 is acidic, and above 7 is alkaline.
  • Most commonly grown turfgrasses do best at a pH in the 6.0 to 6.5 range.
  • In areas of already low pH (less than 5), acidifying fertilizers may be of concern.
    • Low pH reduces the population of earthworms and certain microbes.
  • In Minnesota and many other parts of the Midwest, pH tends to be rather high (above 7) along with high buffering capacity.
    • Buffering capacity refers to the soil’s ability to resist pH change.
    • In a soil with high buffering capacity, it is very difficult to reduce the pH using fertilizers and other soil amendments.
    • In those soils, the use of acidifying fertilizers may actually be beneficial. 

Authors: Sam Bauer, P.G. Johnson and D.B. White

Reviewed in 2024

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© 2025 Regents of the University of Minnesota. All rights reserved. The University of Minnesota is an equal opportunity educator and employer. This work is supported by the U.S. Department of Agriculture’s National Institute of Food and Agriculture.