Fall is a good time to do a soil test

Before setting your garden to rest for the winter, think of ways to improve your garden soil for next year’s crop. A healthy garden soil is the foundation for successful gardening, and a simple soil test can reveal the existing nutrient levels in the soil and help in strategizing your efforts to improve the soil condition.

Why soil test?  Too often we take a blind approach on ways to improve the garden soil by adding fertilizers, micro-nutrients, lime, sulfur, and other materials without knowing its existing nutrient status. This approach can be ineffective in improving the plant growth and can do more harm than good to your soil.

Plants generally respond better to their specific nutrient needs than a generic application. An old saying, “If one pound is good, two are better, and three must be best” doesn’t apply to plant growth and its nutrient need. In fact, indiscriminate application of fertilizer can lead to nutrient leach, alter soil chemistry, and can cause plant injury. Customizing your nutrient application to the plant needs can save cost, prevent plant disorders, and avoid unnecessary waste of nutrients leaching on the soil surface.  A soil test determines the current nutrient status of the soil and recommends the right amount of nutrient application that tailors in with the plant needs.

What nutrients are tested?  A standard lawn and garden soil test analyzes the pH of the soil (measure of acidity or alkalinity), organic matter content, and phosphorous and potassium nutrient level. In addition, the test report recommends appropriate nutrient application based on the given crop. However, the standard lawn and garden soil test report will not analyze the nitrogen level in the soil, as the level of nitrogen fluctuates widely in the soil and the test result cannot be accurately interpreted to meet the plant need.  For other soil nutrients like calcium, magnesium, zinc, boron, and soil contaminants like lead can also be tested for an additional cost. For more information, visit the UW Soil and Forage lab website at https://uwlab.soils.wisc.edu/fees/.

Soil test timing:  Fall is one of the best times of the year to test your garden soil, as it gives considerable time to amend the soil for pH. You can also plan ahead to compost appropriate quantities of organic matter in the fall season based on the soil test report.  In general, it is best to test your garden soil once every three to five years.

How to take a soil sample for testing:  To ensure an accurate test result, a good representative soil sample of your garden is critical. Collect soil samples from at least 10 random spots that well represent your garden area. You can use a soil probe, shovel, trowel, or soil auger for collecting samples. In each spot, remove any mulch or compost or sod laying on the soil surface and using the probe, collect the soil sample core from the top 5 to 7 inches. Mix all the soil sample cores collected from the 10 random spots in a big container and scoop out one cup from the container in a clean plastic bag, and label it.

What is the cost and where to ship the soil samples?

You can ship soil sample to UW Soil and Forage lab along with its submission form at 2611 Yellowstone Dr., Marshfield, WI 54449.  Download the soil submission form at https://uwlab.soils.wisc.edu/soil-samples/lawn-garden/ .   The cost for standard soil analysis is $15 per sample and it takes about 10 business day to get your soil test report. For more information visit UW Soil and Forage lab at https://uwlab.soils.wisc.edu/soil-samples/lawn-garden/

For any garden inquiries, contact us at planthealth.advisors@extension.wisc.edu or call/text at 608-298-6945. For more info, visit us at: go.wisc.edu/planthealthadvising

Author: Vijai Pandian, Horticulture Educator


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