Unfortunately, not everyone (actually hardly anyone) has the ideal soil for growing ornamental plants in the landscape. Such a soil would be light and airy with great drainage and enough organic matter to support a thriving population of soil organisms. It would hold water and nutrients in the root zone of the plants and would not change much regardless of the foot traffic that travels over it.

Well, there certainly are naturally occurring soils that meet these criteria. They generally have the term "loam or loamy" attached to them. But, for many of us, our landscape soils will present certain "challenges" that we must attempt to address if we are to have success with our plants. These would include:

Heavy or Clay Soils - Clay particles are extremely small and generally flat in nature. They pile on top of each other resulting in an extremely tight fit. This leaves no space for air or for water to move so these soils are characterized as being poorly drained and subject to compaction. They often form a hard surface that does not allow seedlings to emerge or for water to penetrate. These are tough soils in which to grow plants!

What to do about it - Adding large amounts of organic matter (OM) such as compost, peat moss or other such products will improve clay soils. The OM will help to form larger clumps which will have bigger pores for air and water. This helps with root growth and improves drainage to make the soils more plant friendly.

Light or Sandy Soils - Just the opposite of clay, sandy soils are made up of relatively large particles. This results in very large pore spaces which result in water moving through rapidly. That is why these soils tend to be "droughty" and require more frequent watering. Also, sand has a poor electrical charge and does not hold onto nutrients like clay. This allows the nutrients to also flush through the soil quickly along with the water.

What to do about it - Adding large amounts of organic matter (OM) such as compost, peat moss or other such products will improve sandy soils. The OM will "clog" the large pores and absorb water as it moves through making it available to plant roots. Also, OM has a great ability to hold onto vital plant nutrients so they are not so easily leached through the soil.

Soil Compaction - This occurs when the 50% pore space of an ideal soil is squeezed together and lost. Without adequate poor space, there is not enough oxygen or water for proper root growth. It is a primary problem of clay soils which already have limited pore space and the small particles are inclined to compact together. Vehicle traffic such as construction tools, lawn mowers and even foot traffic all contribute to compaction.

What to do about it - Adding large amounts of organic matter (OM) such as compost, peat moss or other such products will improve clay soils and thus minimize compaction. The OM will help to form larger clumps which will have bigger pores for air and water. This helps with root growth and improves drainage to make the soils more plant friendly.

Tilling the soil can also help eliminate compaction. That is why it is a good idea to double dig new beds and borders to loosen the soil. In lawns, core aeration will help minimize the problem. Removing cores of soil to a depth of about 2 inches or more will allow air and water to penetrate into the root zone of the turfgrass.

Subsoil as Topsoil - Unfortunately, during the construction of houses, the contractor is required to dig a basement that is 7 to 8 feet deep. This requires excavating many cubic yards of subsoil which needs to be removed. All to often, this soil is merely spread out over the lot on top of the existing topsoil. What's even worse is that it may then be pounded down under the weight of earth moving equipment or trucks.

Plants are meant to live primarily in a layer called the topsoil. This is usually the top 6 to 18 inches of soil that contains organic matter and has a structure capable of supporting plant life. Beneath this layer is a type of soil called subsoil. It does not have the organic matter or physical structure needed for plant life. It will often be a fine textured soil that will become very hard once it is spread out onto the surface.

What to do about it - Adding large amounts of organic matter (OM) such as compost, peat moss or other such products will improve subsoils and thus minimize compaction. The OM will help to form larger clumps which will have bigger pores for air and water. This helps with root growth and improves drainage to make the soils more plant friendly.

In some cases, you may need to either replace the layer of subsoil or add significant amounts of good, loam topsoil. Remember, that to grow good turfgrass you will need at least a 6 inch layer of the topsoil. Adding a few inches will not do the job.

Shallow Soil - In some areas, there may be only a few inches of actual topsoil on top of a rock hardpan layer. This is generally not enough to grow most ornamental landscape plants. Some of them may survive on this limited topsoil layer but few will thrive over the long run.

What to do about it - You may need to add significant amounts of good, loam topsoil to improve this type of situation. Remember, that to grow good turfgrass you will need at least a 6 inch layer of the topsoil. Adding a few inches will not do the job.

In the extreme, you will need to choose your plants carefully. This is especially true with trees and shrubs that need to develop extensive root systems. There may be species that can survive better under thin topsoil conditions. Often plants that are native to the area have shown that they are adapted to it.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

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