Once the landscape planting site has been selected, one of the first priorities before planting is to test the soil to determine the pH, the lime test index and fertilizer needs. It is much easier and more desirable to adjust the soil pH and nutrient status before planting. Ideally, the initial soil samples should be taken and corrective actions done a year or two prior to planting to allow time for the needed soil amendments to produce their most desirable effects.
A soil analysis is most valuable in established plantings when used in conjunction with foliar analysis. Because of the vast depth and breadth of the root systems of woody plants, it is difficult to take a sample that will represent the entire area where the root system absorbs its nutrients. Therefore, a poor correlation may exist between soil test and leaf analysis results for a given nutrient. A foliar analysis does not indicate soil pH, so both should be used to help diagnose suspected mineral deficiencies. Soil tests should always accompany foliar analysis of plants in tubs or planters, because the pH of soil in containers can change rapidly.
Test soils in the landscape every three years and take corrective action. Sample at least eight sites in an average size lot, and combine and thoroughly mix them. Dry the soil at room temperature and place a cupful in a sample box available from county Cooperative Extension Services offices.
For homeowners, areas near the house are likely to be different from those a few feet away. Carefully evaluate your lot to determine where subsoil has been exposed in the process of grading around the building.
If the soil varies around the home, take a composite sample from each distinct area. A composite sample made up of samplings from two distinctly different areas does not represent either area.
Taking the Sample
Sample a given area about the same time each year-- nutrient availability may vary with time of sampling.
From each predetermined area, regardless of size or use, prepare a composite sample by taking no fewer than eight samplings consisting of vertical columns or cores of soil approximately 2 inches by 2 inches by 12 inches deep, or 2 inches in diameter and 12 inches in depth.
It has been found that eight well taken samplings or soil cores per composite sample from a given area regardless of size, will yield laboratory test results that can be duplicated much more frequently than tests based on samples made up of one or three samplings.
Avoid sampling unusual areas--those close to roads, the foundation, previous locations of compost or manure piles, fences, sidewalks or poorly drained areas--unless such locations are sampled and packaged separately.
Subsoil samples taken at a depth of 18 to 24 inches, especially with organic soils, will often aid in making lime recommendations. Subsoil samples need not be composites.
Break Clods--Mix Thoroughly
As you take the individual 1-cup samplings, place them in a plastic pail until you have eight from the area involved. Then mix the soil in the pail thoroughly with your hands while holding the pail at an angle of 45 degrees and turning it. Do not use a metal pail if the sample is to be tested for micronutrients.
If the soil is very wet at sampling time, it may be necessary to partially air dry the sample to obtain an adequately mixed sample. To prevent inaccurate test results, avoid drying the sample with artificial heat or in areas containing ammonia or other gases.
If the soil is very dry it may be necessary to crush the cores to get a good mix. A clean wooden surface and a rolling pin work well.
Preparing and Packaging the Sample
After the sample is thoroughly mixed, place a pint of the soil in the container for sending to the testing laboratory. You can buy special boxes provided by the MSU Crop and Soil Sciences Department at your county Extension office or directly from the MSU Crop and Soil Sciences Department. Purchase the soil container pays for the soil test.
If these are unavailable, any clean container of one- pint capacity that can be tightly closed should prove satisfactory. Do not use rusty or otherwise contaminated containers, such as metal cans--any foreign material may affect the soil test.
Drying the soil samples prior to analysis may cause changes in the availability of certain nutrients particularly phosphorus. Do not force-dry the samples by placing them on radiators or inside ovens before submitting them to the laboratory.
Provide Complete Information
The more complete the information you provide, the better the fertilizer recommendation.
Use a waxed pencil or pen to fill in the information requested on the special soil container, or if you use some other container, label the package with the owner's name and address.
The following information should accompany the sample:
1. Previous land use.
2. Ornamental species, whether new or established plantings.
3. What weed killers have been used?
4. Good or poor drainage?
5. Soil type, series or soil management group name, if known.
6. Whether irrigation is to be used.
7. Special problems or conditions.
Information on the various soil tests available from the MSU Soil Testing Laboratory is available from your county Extension office.
The interpretation of the soil test results and the fertilizer recommendations will accompany your soil test report. Contact your garden center, retail nursery or county Extension office for pertinent and timely publications.