Preparing the soil is the most important step in flower or vegetable gardening. Test your soil this spring and use the test results and recommendations as a guide.

The soil in gardens changes, although it may look the same year after year. Growing and harvesting crops, leaching and erosion affect the availability of soil nutrients. A soil test is a valuable tool that guides gardeners.

A soil test measures nutrient amounts and pH, or level of acidity. Soil pH is measured on a scale of 0 to 14, with 0 being the most acid, 14 the most alkaline and 7 neutral.

Most soils naturally have pH levels ranging between 5 and 8. Many flowers and vegetables do well in a range between 6 and 7, so chances are you won’t need to change your soil’s pH much.

Don’t guess when it comes to fertilizing and changing pH. Over-applying chemicals can harm soil and plants, as well as pollute groundwater and streams.

Excess lime raises the soil’s pH above what plants can tolerate, makes it more difficult for them to draw nutrients from the soil, and slows growth of beneficial soil microorganisms. Some flowers prefer a more acid soil and can suffer from iron deficiency if you apply too much lime.

Soil-test mailing kits are available at Penn State Extension offices for $9. Penn State soil-test mailing kits include instructions for collecting soil samples and sending them to Penn State’s soil-testing laboratory.

You will receive test results in about two weeks. Results include levels of potassium, calcium, phosphorus and magnesium, along with the soil’s pH. Also included are recommendations for the kinds and amounts of fertilizer to apply and how much lime, if any, to add to the soil.

If you are planning to grow rhododendrons, azaleas, laurels or other flowers that prefer acid soil, you may need to apply a chemical such as sulfur, which lowers pH. Apply no more than the recommended amount.

Till the recommended materials about five inches into the soil. While working the soil, remove stones, sod clumps, weeds and debris. Incorporate several inches of organic matter.

Composted kitchen scraps, well-rotted manures, lawn clippings and decayed plant material are all good forms of organic matter. They help retain water and supply some nutrients for all plants set into the soil.

Add two to three inches of organic mulch on top of the soil around your plants. Mulch helps keep soil moist, prevents erosion, discourages weeds and builds up the soil’s organic matter.

Mulch also tends to be more attractive than bare soil in an ornamental garden. It keeps mud from splashing on your flowers and gives the ground’s surface uniform color and texture.

Several kinds of mulch are available at garden centers, including wood bark chips, shredded bark and peat. If you use grass clippings, leaves or well-decayed compost, periodically loosen them with a hand cultivator or hoe to prevent surface-crusting.

Finally, retest your flower and vegetable garden’s fertility and pH levels each year for several seasons. If reports remain similar, you can reduce sampling to every three to four years. Nutrient levels and pH gradually change over time. It is important to keep monitoring the soil to keep levels optimum.

“Growing Green” is contributed by Lehigh County Extension Office Staff and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-746-1970.