A simple soil test will measure the pH of your soil, showing whether it is acidic or alkaline. More thorough tests also measure the soil salinity and the amount and availability of nutrients a soil contains that your plants need to grow. Testing your soil so that you know how to improve it will increase your chances of success at growing berries, vegetables, flowers, ornamental shrubs and fruit trees.
The most important thing a test can reveal is the pH of soil. The pH scale measures the acidity or alkalinity of soil. The scale runs from 0, the most acidic, to 14, the most alkaline. The pH of water, 7, is neutral. The pH scale is algorithmic, based on the power of 10; a soil pH of 5 is ten times more acidic than 6.
Micronutrients--including copper, iron, manganese and zinc--are less available to plants when the pH of a soil rises above 6.5. Slightly acidic soil of 6.1 to 6.9 is best for most flowers, shrubs, vegetables and turf grasses. Knowing the pH of your soil can help you decide what cultivars to plant.
Testing Eliminates Guessing
Adding lime raises soil pH; adding sulfur lowers it. If you raise the soil pH above the tolerance level of your plants, they may be unable to extract nutrients they need to grow. Soil testing can help you decide which and how much of these ingredients are necessary to properly amend your soil.
Adding compost, manure or fertilizer can change your soil. So can drought, erosion, heavy rainfall and harvesting crops. These can all effect the amount and availability of nutrients that plants need to grow, flower and fruit.
A full test of soil includes a measure of soil pH plus the amount of calcium, magnesium and phosphorous that is available to your plants. You need to know how much of these essential micronutrients your soil has if you are to accurately correct deficiencies.
Soils with pH 8 or higher have a high salt content. Plants vary in their ability to tolerate saline soils. Knowing whether your soil is saline will also help you select plants that are most likely to succeed. For example, asparagus, barley, bermudagrass and cotton grow well in salty soils. Celery, green beans, spinach and most fruit and nut trees do not.
How and What to Test
Test your soil at least once every three years. Collect soil samples for testing any time of year. You do not have to wait until you are ready to plant.
Take separate samples of soils that you use to grow flowers, lawns and vegetables. If you are growing plants in different types of soils, especially clay or sand, take separate samples of each type of soil. Take separate samples if the soils are a different color. The plants in each of these soils may have different problems; you may need to amend the soils in separate ways.
Many garden supply centers sell simple soil testing kits. You arrange for more sophisticated testing at most state agricultural extension services.