Campbell Vaughn: Soil sample can reveal solutions for landscape

We answer landscape questions daily here at the Extension Office. Most involve “What do I need to put on my (blank) to make it (blank)?”


Applying lime, fertilizer, and pesticides are the most common recommendations to solve a number of issues, so I want to simplify liming and fertilizing.

An underlying cause of poor fertility in Georgia is overly acidic soil. Soil pH strongly influences plant growth, nutrient availability, and microorganism activity in the soil. It is important to keep soil pH in the proper range to obtain the best yields and high-quality growth. A pH that is too low or too high can cause nutrients to become unavailable to plants. In other words, your plant isn’t eating unless the pH conditions are more ideal. Until the pH is in the correct range, don’t waste expensive fertilizer on your plants when it isn’t going to get absorbed.

The first step in growing healthy plants is to take a soil sample to help determine pH and nutrient levels. Instructions for taking a soil sample can be found on our website ( or our offices, 602 Green St. in Augusta or 6420 Pollards Pond Road in Appling.

When taking a soil sample, make sure you have a separate sample for each different area. Collect one sample to test for the lawn and another for an ornamental shrub bed, or vegetable plot. Be sure to label them accordingly. The lab will send an analysis and recommendation for that plant. I like to write notes like “established Zoysia, perennial bed, new Bermuda sod or veggie raised bed” on the sample bag under the type of crop to get back a schedule for additives.

Soil samples should be conducted every 3 years in sandy areas and every 5 years in clay areas. Take these samples in the fall if possible.

The pH range for most plant growth is 6.0 to 6.5. Most ornamental shrubbery in our area tends to thrive with moderate acid levels. Grass lawns tend to like a more neutral pH. Your soil test results will tell you exactly how much of each nutrient needs to be added for optimal plant production.

When applying lime, use dolomitic lime, which contains calcium and magnesium carbonates to increase the soil’s pH. Use a lime that has at least a 70 percent pass-through using a 100 mesh screen. That pass-through test will be listed on every bag of lime. A higher quality lime will result in a higher pH at a much quicker rate.

Once the pH is correct for the plant, fertilizers can be used to feed plants effectively. There are different categories of elements that make up fertilizers and they are called “major, secondary, or micronutrients.” There are also three major nutrients plants must have – nitrogen, phosphorus, and potassium.

Nitrogen, the element that is most used by a plant, promotes growth. Soil samples do not reveal nitrogen levels because it moves rapidly through the soil as well as the plants. These levels can change daily. Grass is greenest and grows fastest when there is plenty of nitrogen available.

Phosphorus enables the transfer of energy throughout the plant, which aids root development and flowering. It will be listed on a soil sample result with a recommendation of a how much, if any, might need to be added to the soil.

The same thing applies to potassium, which is critical for dealing with stress and fighting disease.

On any bag of fertilizer, you will see three numbers that represent the three major elements needed – nitrogen, then phosphorus and finally potassium.

A soil sample may recommend a fertilizer for early season grass “green up.” The recommended blend might be labeled 16-4-8. That means 16 percent of the bag is nitrogen, 4 percent is phosphorus and 8 percent is potassium. Blends vary for seasonal growth, as well as different varieties of plants.

Plants also need second-level elements – calcium, magnesium and sulfur, which help with structure, growth and development. Calcium and magnesium are easily supplemented with the dolomitic lime. Sulfur may need to be added separately unless it is in a fertilizer mix.

The next level, micronutrients, are traces of elements like boron, chlorine, copper, iron, manganese, molybdenum, and zinc. These are mostly deficient when the soil pH is too high or too low.

With an accurate soil test, the proper additives, and timely application of nutrients to your soil, your plants should flourish.