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Troup extension agent: Figuring out which fertilizers to use

By Brian Maddy

Contributing columnist

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At this time of year all the garden centers are bustling. Homeowners are intent on getting their lawns and gardens looking just right.

One area folks often get confused about is what kind and type of fertilizer to purchase. The first question that should come to mind is how much do I need.

The only way to know is to do a soil test. The UGA Soil Testing lab has been doing soil tests for many years and has honed their recommendations down well.

Taking a representative soil sample is relatively easy. Once you deliver your soil sample to the extension office, it takes about a week to obtain the results. Email will speed it up.

The cost is $9. The soil test results will provide fertilizer recommendations for the type of crop that you have selected.

The next step is to purchase the fertilizer. Sometimes the recommended fertilizers are at the store and sometimes not. This is where figuring out fertilizers comes in handy.

The first thing that usually needs to be corrected is the pH. The pH measures the acidity and alkalinity of the soil. Georgia soils are naturally acidic.

Most plants require a slightly acid soil, 6.0 to 6.5. The range is from 0 to 14 and neutral is 7.0. If the pH goes below 6.0 the nutrients become unavailable and other nutrients become available and may cause toxicity to plants.

If the pH goes above 7.0 the same results occur. Much of our American West is an alkali desert.

To correct pH, lime needs to be applied. If your soil test report indicates that magnesium is needed, a dolomitic limestone should be purchased since it contains magnesium. Otherwise, calcitic limestone is the correct choice.

The finer the limestone, the faster it will react with the soil but it will be harder to spread. The lime that is the consistency of sand spreads well through a mechanical spreader.

It takes about six months or so for the pH to be corrected. So the sooner you start, the better.

Homeowner recommendations usually specify spreading so many pounds per 1,000 square feet. Measure off 1,000 square feet — 20 feet by 50 feet — to get an idea on how much needs to be spread.

If you have a pull-type spreader, you may have to run some practice runs to get an idea of how fast you have to go and what size opening you need to use. You may want to use some inexpensive kitty litter to practice with.

The three primary nutrients are nitrogen, phosphorus and potassium, N-P-K for short. They are called primary because they are required in the largest amounts.

Numbers in that order are required to be displayed on all fertilizer containers. The numbers represent the percentage of that nutrient in the container.

For instance, 13-13-13 represents 13 percent nitrogen, 13 percent phosphorus and 13 percent potassium. In 100 pounds of triple 13, there is 39 percent fertilizer and 61 percent inert materials that may be used as carriers for the fertilizer.

The larger the number, the less fertilizer you have to spread. You would have to spread twice as much 5-5-5 as 10-10-10. Reading the container label is very important.

Some lawn fertilizers are formulated with a high nitrogen component and the phosphorus and potassium are in a 1-to-2 ratio such as a 28-4-8. Remember that warm season grasses do not need to be fertilized until June, and split the application for later in the summer.

Fertilizers can be coated or encapsulated in order to release their nutrients at a slower rate. These work well in pots and containerized plants. Other fertilizers are designed specifically for roses or azaleas. Azaleas, rhododendrons and blueberries require acid soils and their fertilizers are formulated accordingly.

Water-soluble fertilizers are usually more expensive, but the plant takes them up more readily. A good rule of thumb is to begin by halving the recommendation to start. This prevents six-foot tall tomato plants with no fruit. Then adjust accordingly.

What’s going on in Extension?

Vidalia onion sales are back! Help support 4-H by purchasing Vidalia onions. Onion sales help send kids to 4-H camp. Call the Extension office for more details. $10 per 10 pound bag. Orders must be received ASAP. 706-883-1675.

Monday, April 18, 7 p.m. Troup County Association of Beekeepers, Ag Center.

Tuesday, April 19, 7 p.m. Troup County Cattleman’s Association; Wes Smith, guest speaker: “Cow efficiency.” Ag Center.

Thursday, May 5, Timber Growers, guest speaker Ben Jackson, “Soil mapping.”

Brian Maddy is the ANR Agent for Troup County Extension. The Troup County Extension office is located at 114 Church St. in LaGrange and may be reached at 706-883-1675, Monday–Friday 8 a.m.–noon and 15 p.m.