Many times county agents hear gardeners say: “I used to grow a beautiful garden in this spot, but for the last few years it has gotten progressively worse.
This has happened in spite of the fact that I fertilize heavier, water more, and use better varieties. I don’t know what to do next.”
Chances are these gardeners may have neglected an important task — soil testing to determine soil pH and fertilizer needs.
As heavy rates of nitrogen fertilizer are used over a period of time, the soil becomes more acidic.
Oldtimers used to say the soil got sour and wouldn’t grow anything until it was “sweetened” by lime. Although this is not a scientific description, it does a pretty good job of describing the situation.
Most vegetables grow best at a pH of 6.0 to 6.5, slightly acidic.
(Irish potatoes are an exception; they will get a disease called scab at a higher pH and do best around 5.5 to 5.8.)
To keep the pH above 6.0, garden soil should be tested each year to determine if lime is needed. This should normally be done in the fall, so lime (if needed) can be worked in several months before spring planting. The main purpose of applying lime is to correct the pH. But it also supplies needed calcium and magnesium (if dolomitic lime is used).
Both of these nutrients are needed by garden vegetables.
Why is maintaining a proper pH so important to the gardener? One of the main reasons is that it affects the availability of plant nutrients.
When the pH drops too low, a good portion of the nutrients become tied up and unavailable to the plants.
Maintaining a pH of 6.0 to 6.5 helps insure the availability of most elements needed to make plants grow properly. Adding extra fertilizer in a low pH situation does not compensate for the low pH because many of the added elements quickly become tied up, too.
Symptoms of low pH vary with different vegetables. Basically, the plants remain small or stunted and usually show poor leaf color.
In addition to these symptoms, marginal browning may occur on the leaves.
Actually symptoms can vary considerably depending on which nutrient or nutrients are deficient or toxic. Vegetable yields are reduced progressively as the soil becomes more acidic. Little or no yields are obtained with a pH around 4.5 to 5.0.
Soil test bags and information on how to take a representative soil sample are available at the Dawson County Extension Office. The total cost is only $8 per sample, which includes postage. Take advantage of this opportunity and use it as another tool in producing a good garden. And don’t forget, fall is the best time to test garden soil.
Clark Beusse is the Dawson County extension agent. For more information, call (706) 265-2442.