Start preparing for this year’s garden with a soil test – The Mercury News


Cultivating a beautiful landscape starts with the ground under your feet. The best place to start building a healthy soil foundation is with a soil test. The results will tell you what type and amount, if any, of fertilizer is needed for the plants you are growing. Using the right type and amount of fertilizer is also good for your budget and the environment.

Test the soil when starting a new garden or a struggling garden. Since soil and fertilization practices vary widely, collect and submit separate samples for each garden bed or landscape area to be tested. Repeat every four or five years to check the maintenance of your garden.

You can perform a soil test whenever the ground is not frozen and you have not recently fertilized. Early spring and fall are good times because you can make necessary changes when preparing your garden.

Contact your local extension service for details on submitting a sample. If they don’t have a soil-testing lab, they’ll likely recommend a state-certified lab that tests lawn and garden soils, or you can search the Internet for a certified lab near you.

Collecting a soil test sample is simple. Use a clean trowel and bucket to collect a soil sample.

Drag any mulch or debris to the surface of the soil. Use a trowel and remove a chunk of soil four to six inches deep and where the plant roots are growing.

Take several samples from the garden you want to test. Collect samples from each edge and several in the middle of the bed. Mix them together and place about a cup of soil in a plastic bag or one provided by the lab. Be sure to complete and include the submission form. This includes a place to list the types of plants that will be grown in the sampled area. The lab uses this and the test results to make fertilization recommendations. Send the sample and form together to the soil testing lab.

Allow several weeks for the test to complete and results to be returned. Most basic soil tests show the amount of phosphorus and potassium in the soil. Phosphorus promotes flowering, fruiting and root development. Potassium promotes drought tolerance, disease resistance and hardiness. Many soils are rich to excessive in these plant nutrients. You cannot remove the excess, but you must avoid making the problem worse. Soil test reports can help you do that.

Most labs don’t measure the amount of nitrogen in the soil because the levels change quickly and aren’t easy to test accurately. Instead, they make nitrogen recommendations based on the plants you are growing or will be growing in the tested area.

Soil pH is also measured in most soil tests. Acidic soils with a pH below neutral (7.0) are often called acidic, while alkaline soils with a pH above 7.0 are called soft. Soil pH influences the nutrients in the soil that plants can absorb and use for growth. Blueberries, azaleas, and red maples are examples of acid-loving plants. Clematis, crabapple and spirea are some of the alkali tolerant plants.

Always use soil test results when trying to change pH. Lime is used to soften soils while sulfur is often used to lower pH. Using too much or the wrong amendment can negatively impact the health and productivity of your garden. Undoing bad apps can take years to fix. Growing plants adapted to soil pH may be the best solution for those whose soil pH is acceptable, but not ideal.

Include soil tests when planning new gardens or helping those in trouble. Understanding your soil can help you create a solid foundation important for the health, longevity and beauty of your gardens and landscapes.

Melinda Myers has written over 20 gardening books, including The Midwest Gardener’s Handbook, 2nd Edition, and Small Space Gardening. She hosts The Great Courses DVD series “How to Grow Anything” and the nationally broadcast television and radio show Melinda’s Garden Moment. Myers is a columnist and editor for Birds & Blooms magazine and was commissioned by Summit for her expertise to write this article. Her website is


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