Topsoil is a mixture of organic and inorganic material, water and minerals. Naturally made topsoil takes a century to develop. This mixture is what plants use for development, and it's important to know how to mix topsoil for optimum plant growth. To understand topsoil you must also understand what goes into the creation of topsoil as well as the proper amounts of each element of the topsoil. Simple tests done on-site can help determine this.
Dig up 12 inches of the existing soil in the area where you will be placing the new topsoil. Dig up the entire area where you are replacing the top soil. Remove large rocks or other debris in the soil.
Determine the composition of the topsoil by performing a jar test. Fill the jar with clean water to two-thirds full. Collect topsoil and place it into the jar until the jar is filled to within an inch of the top. Screw the cap onto the jar tightly. Shake the jar vigorously to mix the water and soil. Allow the soil in the jar to settle for one minute. Use the marker to mark the location on the side of the jar of the soil layer that has settled. This is the sandy soil, and the heaviest soil. Allow the remaining top soil to settle for one hour. Use the marker to mark the level of the new layer of soil. This is the silt layer. Allow the remainder of the soil to settle for 24 hours. Use the marker to mark the level of the last layer of soil. This is the clay layer.
Study the marks on the side of the jar. Your topsoil should be one-third sand, one-third silt and one-third clay. Determine which, if any, of the three must be added to the soil to create this measurement. Add the needed material and retest the soil. Continue this process until the topsoil reaches this mixture.
Mix the required missing material into the remainder of the top soil. Retest the soil using the jar-test method in at least four random locations (more depending on the size of the work area) to gain consistency. Add compost and cow manure to the soil until the topsoil is roughly 25 percent organic matter. This will ensure you have nitrogen-rich material going into the soil and the plants when you start planting.
Use the pH kit from a garden supply store to check the pH level in the topsoil. Aim for a range between 6 and 7.5. Add lime to the soil and mix for pH levels below 6.