Home Tips & Advice > Learning Guides > Learn About Fertilizers


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All lawns are deficient in nitrogen because grass quickly uses up the natural supply. Some also need phosphorus and potassium.

There are three common types of fertilizers: natural organic, inorganic and synthetic organic.

Natural organic fertilizers, such as manure, do not dissolve in water. They are converted to usable forms by microorganisms in the soil. They help to create proper physical growing conditions, but can add disease or weeds to the lawn.

Inorganic fertilizers (ammonium nitrate and ammonium sulfate) do dissolve in water and become readily available to plants. They can cause fast growth for a few weeks, but can also cause foliage burn if improperly applied.

Synthetic organic fertilizers (ureafoam, methylene urea) provide a combination of slow and fast release of nitrogen, combining the best of the other two kinds of fertilizer.

Dry fertilizers come in several forms which combine all three nutrients and can range in weight from 14 to 70 lbs. for a typical-sized lawn.

Simple-mix fertilizers are mixtures of the three primary nutrients in a bag. The granules differ in weight and texture so that the heavier ones may work toward the bottom of the bag or spreader. The result is uneven distribution.

Pelletized fertilizers combine all the nutrients into semi-rigid pellets or capsules. This does not ensure a steady release of nutrients unless slow-release sources are included in the pellets.

Trionized fertilizers have the three nutrients bonded into a lightweight carrier such as vermiculite. Nutrients are uniform throughout the granules.

Polyform fertilizers require no added carrier, resulting in the lightest-weight fertilizers. A mixture of the three nutrients is screened to uniform size, putting a high proportion of nutrients into the bag.


Can you get along with just one application of fertilizer?

Yes, but the lawn won't be very healthy. Two feedings are minimum, although most turf experts believe three feedings- or more-are best.

When only two feedings per year are done, they should be done in the early spring and early fall. Each feeding actually serves a different purpose in helping grass grow.

A late winter feeding aids the lawn in early greening and building roots. The late spring feeding builds tillers or sideshoots that help fill in bare spots in the lawn.

A midsummer feeding makes a lawn more drought resistant. The fall feeding helps grass build more sideshoots or tillers and underground stems or rhizomes to thicken up a lawn. It is considered the single most important feeding of the year.

Apply fertilizers in both directions to avoid streaking or missed strips.


Every fertilizer consists of three nutrients, always listed in the same sequence in the formula, which must be printed on the bag or label.

Each ingredient serves a separate function in enriching soil and stimulating plant growth. Listed in order, they are:

Nitrogen (N) - vital to plants for foliage color and density and for root growth. This is the primary nutrient that needs to be replaced.

Phosphorus (P) - for seedling development, cell building and root growth.

Potassium (K) - assists plants in forming starches and proteins and helps them resist disease and environmental stresses.

Sulphur and iron are two other important ingredients to look for in fertilizer. Both are needed to keep the grass from yellowing and to continue growth.

Each nutrient is designated by a number-a percentage of the pounds of each per hundred pounds of fertilizer.

For example, a very common 20-10-5 formulation means there are 20 lbs. of nitrogen per hundred pounds of fertilizer, 10 lbs. Of phosphoric acid and five lbs. Of potassium.

In a 50lb. bag with the same formula on it, there would be 10 lbs. Of nitrogen, five of phosphoric acid and two and a half of potassium.

While formulations vary, the most common are 20-10-5, 5-10-5 and 10-6-4, but others being offered include 24-6-6 and 23-7-7.

When you select a fertilizer, remember the purpose of each ingredient and relate the percentages to the needs of your plants and/or lawn.

Most fertilizers indicate on the package the number of square feet they will cover. To help figure out the amount you will need, take the size of your lot, and subtract the square feet of the house, garage and driveway.


While a 10-5-5 mixture may cost only two-thirds the price of the 20-5-5 mixture, it is delivering only half the needed nitrogen.

Fertilizers with slow-release or slowly available ingredients cost more because they dissolve gradually and give prolonged fertilizing action.

With some types of dry fertilizer, there is considerable danger of "burning" the lawn if applied too heavily or not watered immediately. Also, grass fed with a fast-acting fertilizer can be weaker and more susceptible to disease because it grows too fast.

Urea formaldehyde (or urea foam) is a good slow-release source of nitrogen, whereas urea alone or other mineral sources of nitrogen dissolve quickly.

Fast-acting inorganic fertilizers, with lower price points, appeal to price-conscious consumers. Remember that the numbers don't tell the whole story. The important part is how the grass responds and thrives.


Specialized fertilizers, in dry or liquid form, are manufactured for specific plants. The best way to learn about the specific merits of each product is to study manufacturer's literature.

The local agricultural extension agent is also a good source not only for product knowledge, but for information about the soil conditions, growing needs and special characteristics of your area.

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Check your state and local codes before starting any project. Follow all safety precautions. Information in this document has been furnished by the North American Retail Hardware Association (NRHA) and associated contributors. Every effort has been made to ensure accuracy and safety. Neither NRHA, any contributor nor the retailer can be held responsible for damages or injuries resulting from the use of the information in this document.

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