Fertilizer: Why Do You Need It?

All lawns are deficient in nitrogen because grass quickly uses up the natural supply; some also need phosphorus and potassium. Fertilizers help to replace these ingredients for a healthier and greener lawn.

The Three Common Types of Fertilizers

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.

Other Types of Fertilizers

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.

What in the World Does 10-5-5 Mean?

Have you ever taken a look at a bag of fertilizer and wondered what that three-digit number on the front meant? Every fertilizer consists of three nutrients, which are always listed in the same sequence to make up a three-digit formula. Each ingredient serves a separate function in enriching soil and stimulating plant growth. Listed in order they are:

Nitrogen (N): this is 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 seeding development, cell building and root growth.

Potassium (K): assists plants in forming starches and proteins and helps them resists disease and environmental stress.

Each of these three nutrients is designated by a number - a percentage of the pounds of each per hundred pounds of fertilizer. For example, a vary common 20-10-5 formulation means there are 20 lbs. of nitrogen per hundred pounds of fertilizer, 10 lbs. of phosphoric acid and 5 lbs. of potassium. In a 50 lb. 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 formulas 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.

How To Figure Out How Much Fertilizer You Will Need

Most fertilizers indicate on the package the number of square feet the will cover, but 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.

How Many Feedings?

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.

back to top