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The optimal pH of your vegetable garden should measure about 6.5, just below neutral. The pH of soil determines, in part, the availability of the different nutrients plants require for their survival. Failure to provide adequate soil conditions can cause stunted growth and yellow foliage with prominent green veins. If you have an alkaline soil -- soil where the pH measures above 7 -- you may want to consider amending the soil to lower the pH. Applying sulfur is one way gardeners modify soil conditions to promote optimal growth of their vegetable plants. While its best to adjust the pH before planting, you can also modify the pH around existing plants.
Collect a soil sample and submit it for a soil test before beginning any soil amendment program. Although plant symptoms can provide a clue about possible pH problems or nutrient deficiencies, since many different problems can produce similar symptoms, you should confirm the problem before attempting a solution.
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Measure your vegetable garden in order to calculate the amount of sulfur to apply. The Purdue Extension recommends applying 1 1/2 lbs. of garden sulfur for every 100 square feet in order to lower the pH one full number. For example, if your soil tests at 8.0, this application rate will lower it to 7.0, an acceptable pH for a vegetable garden.
Add sulfur and work it into the top layer of soil. It may take several months to see results, so it's best to add sulfur in the fall and retest the soil in the spring, repeating the application process if you haven't achieved good results. Do not over-apply sulfur in an effort to speed up the process, as you can cause nutrient imbalances if you lower the pH too quickly.
Remove soil from around the base of existing plants to lower the pH, being careful not to disturb the plants' roots. Mix 2 tsp. of sulfur per cup of soil that you remove. Replace the soil around the plants and water until the soil is moist but not sodden.
Retest the soil regularly and apply sulfur treatments as needed. Vegetable garden soil should range between 6.0 and 7.0.
You may need to add more sulfur to soils high in clay or organic matter. For clay soils, the Oregon State University Extension recommends adding 4 to 5 lbs. of sulfur per 1,000 square feet. Your soil test results should also provide information on soil type.