How Does pH Work?

Sour or Sweet?

Before you settle in next year's garden, treat yourself to a soil-testing kit at the garden center. Follow the directions and find out what kind of soil you are putting your plants in. PH is the measure of acidity ("sourness") or alkalinity ("sweetness") in your soil. Neutral soil can be used for most annual flowers and summer vegetables, but even these plants will do better if your soil is slightly acid. Some plants will not flourish at all in unsuitable soil, so it's a good idea to make sure your soil and your plants will be happy together.

Your Soil Test Shows a pH of Below 7.0

Your soil is acid. You can confirm this by looking at landscape around you. You will probably notice lots of evergreens and probably some oak or maple trees. Your garden will do best if you focus on acid-loving plants, such as azaleas and rhododendrons. Fruit trees and most vegetables like a slightly acid soil (6.0 to 6.5 pH), including those summer tomatoes you want to grow. To keep the slight acidity your soil needs, you can dig in peat moss and use a fertilizer designed for acid-loving plants. Mulch with pine needles, chopped oak leaves and add dig compost into your soil. Sweeten excessively acid soil with ground lime and small amounts of wood-ash from your fireplace (be careful--large amounts of wood-ash combined with water starts making corrosive lye!). Some plants want very acid soil, among them blueberries. To create very acid soil, add elemental sulfur or aluminum sulfate. Your soil needs to be brought down to a pH level of 4.5 to 5.0 for blueberries to do well. Acid soil is most common in areas that get a fair amount of rain. One reason to keep track of soil acidity is because some of that rain is what we call "acid rain." Too much of it, and even acid-loving plants will suffer.

Your Soil Test Shows a pH Above 7.0

Soil in very sandy regions that receive little rain tend to be alkaline. Again, look around. Strongly alkaline soil supports some kinds of cedar trees, date palms, olive trees, agave and yucca plants, portulaca and four-o'clocks, and members of the cucumber family, including melons. Mildly alkaline soil is hospitable to geraniums, celery, collards and other cooking greens. Maintain alkalinity with ground limestone. Reduce alkalinity with peat moss, evergreen needles, and compost; remember that frequent watering will help your efforts. This practice works best in small areas, such as your vegetable garden.

About this Author

Janet Beal has written for Demand Studios since May 2008. She writes about gardening, the home, child development, and cultural issues. Her work has appeared on early childhood education and consumer education Web sites. She has a Bachelor of Arts in English from Harvard University and a Master of Science in early childhood education from the College of New Rochelle.