Gardening Matters

It’s been I while since I mentioned the importance of getting a soil test of your gardening areas. And by gardening areas I mean areas where you deliberately grow something. It could be your lawn, your flower beds, your vegetable patch or whatever.

In my experience, most gardeners tend to follow conventional wisdom and fertilize twice a year, once in spring and once in early summer. Also, we often spread lime on our yards every year. The problem with this is that if you don’t know what kind of soil conditions already exist, you may, at best, be wasting time and money and, at worst, you may do damage to your soil.

Soil tests will tell you the degree of acidity or alkalinity in your soil. This is called the pH factor. The pH scale goes from 0.0 to 14.0. 0.0 is very acidic (similar to battery acid), a 7.0 is neutral and a 14.0 (like drain cleaner) is very alkaline. Most plants in our area thrive at a pH of 5.5-6.5. Some plants, such as acid-loving blueberries, azaleas and rhododendrons, prefer a pH of about 4.0, but will do OK in the 5.0-5.5 range. And if you’re mentally asking, no, I don’t have a clue as to what pH means or refers to. They didn’t tell me that in Mt. Lebanon Senior High School chemistry class and I have never been bothered by it since.

So what’s so important about pH levels? The pH levels determine how effectively the necessary chemical elements in the soil and in fertilizers will be available to your plants. Nitrogen, potassium and phosphorus and a handful of trace elements are needed by your plants to make the food and energy they use to grow. If the pH is too high or too low, these chemicals will stay locked up in the soil rather than be available to help your plants thrive.

I had a lawn service once that informed customers that they would provide an annual application of lime to customers’ yards for FREE. I was at first excited to be getting something for FREE, but then I wondered how they would know how much lime to add to my yard. I asked them if they done a soil test. The answer was “no”, so I fired them. The point being, don’t mess with your soil (or Mother Nature in general) unless you have a basic clue as to what actually needs to be done.

Speaking of nitrogen (N), potassium (P) and phosphorus (K)…these are the three basic chemicals that are in fertilizers. Fertilizers help replenish these chemicals in the soil and make sure that they are in sufficient supply to keep your plants growing whether they are trees, shrubs, flowers or vegetables. The N-P-K numbers on the fertilizer package tell you what percentages of these chemicals are in the package. A bag marked 12-8-8 will have 12 percent nitrogen, 8 percent potassium and 8 percent phosphorus. A bag marked 10-10-10 will have 10 percent of each of these elements in the bag.

A soil test will not only tell you what your pH value is, it will also tell you what level (high-medium-low) your soil has of each of these essential chemical elements. The test will also recommend any amounts of additional N-P-K that you should add to the soil if necessary.

So how do you go about getting a soil test done? You can contact any independent laboratory in the area that offers these services. Even better, you can contact the DeKalb Master Gardener’s hotline at 404-298-4080 or, in Fulton County, at 404-613-7670. Ask them to send you a soil test bag and the instructions for the soil test. Follow the instructions and give them a check for $8.00 for each soil test you want. If you give them your email address you will usually get the results back in a week or maybe less.

If you’re a commercial farmer you should get a soil test every year. Homeowner gardeners will be doing well if they get them every 2-3 years. If you have had a lot of work done on your soil (such as adding a couple of truckloads of amendments) you should get a new soil test after the amendments have had a few months to settle into your garden’s soil.

If you want to know more than you possibly need, check out the Georgia Soil Test Handbook from the University of Georgia’s Agricultural College. ( It’s a lot of information but it can really be helpful in educating yourself about soil and soil testing.

And remember to follow the instructions on any products, such as fertilizer, that you use in the garden. I insist.

Jeff Coghill has been gardening in DeKalb County for more than 35 years and has probably killed at least one of each kind of plant he has tried before getting another one to thrive. He is a gardening volunteer at the Dunwoody Nature Center and works closely with members of the DeKalb Master Gardeners group. He can be reached at

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