Soil Sampling Season

Fall is the time of year that most soil samples are taken. The following are some guidelines for taking soil samples.

• Take soil samples from a uniform depth. Soil tests have been calibrated at the depth of the cultivated layer (6-8 inches) for all but extablished turf. A 7 inch depth should be targeted. This would include areas where new lawns are to be established, flower beds, landscape beds, and areas with trees and shrubs.
• Established turf should be sampled at a depth of 4 inches.
• Use a soil coring tool (soil sampling tool).
• Ideally, a minimum of 20 cores should be taken and composited for a sample. When you mix the cores to form the samples, make sure that you have mixed them well before you take the subsample to send to the lab. All clods or core pieces need to be broken up. The most common mistake in soil sampling is not mixing cores adequately.
• Take cores in a random pattern in the areas sampled.
• Divide landscapes up into sampling areas. Beds, turf areas, and garden areas should be sampled separately.
• If fertilizer has been spot applied to an area (such as fertilizer stakes), samples should stay off of the spots if at all possible. If the spots are not known, then plan to take extra cores.
• Different soil types within a landscape or turf area should be sampled separately.
• Avoid any features in a landscape that might skew the test results. Examples would be disturbed areas (such as where pipes were trenched in), wet pockets, or areas right next to pavement or cement walkways. Do not take cores from these areas for the composite. If you are interested in the fertility of these areas, take separate samples.
• Take samples at least once every 3 years.
• Target soil sampling at the same time of year each time you take the sample. Time of year is not as important as being consistant in when you take the sample. However, fall sampling gives the most consistant results.

Gordon Johnson, Extension Horticulture Agent, UD, Kent County