With all of the questions Extension horticulturists receive each year, few relate to soil care. Soil is a foundation for plant growth and needs to be a focus of garden and landscape management each year.
When the horticulturist asked about soil, it is often being blamed for a problem. A grower will say they’ve tried everything and their plant is still not doing well so it must be due to the soil. I then ask what soil care practices are used and the answer is typically none to very little.
Plants need soil to provide pore space and oxygen for root growth, water and nutrients for plants, and beneficial microorganisms like Mychorrhizae that enhance plant growth.
Important goals for soil management are increasing organic matter, avoiding or relieving compaction, improving drainage or water holding capacity, maintaining a healthy soil ecosystem, and mitigating soil moisture and temperature extremes.
Increasing soil organic matter is one practice that helps achieve many of these goals. Organic matter is decomposed plant material. On soil tests, the organic matter percentage should be close to 5 percent. Instead, it is often only one to two percent.
In sandy soil, organic matter increases water holding capacity. In clay soils, it increases drainage so excess water drains away. It increases soil pore size so roots have more area to grow. It increases plant nutrients. It supports soil microorganisms important to many soil and plant functions. This is why compost is referred to as garden gold.
Organic matter is added to soil when roots die and when dead stems and leaves are incorporated into soil, or when they naturally work their way in via freezing and thawing or through the work of earthworms and other soil critters. This is a slow process and so incorporating organic matter is often used with vegetable and annual flower gardens on an annual basis. In landscape beds with perennial shrubs and flowers, where soil work cannot be done each year, it is more challenging to increase organic matter. In this case, it is best done by adding compost during soil preparation prior to planting. After planting, use coarse organic mulch in place of synthetic or inorganic mulch placed on top of landscape fabric.
As a rule of thumb when adding organic matter to a soil prior to planting, spread two to three inches of compost over the soil and till or spade it in thoroughly six to eight inches deep.
Compost can be added in spring or fall. Undecomposed plant matter, like tree leaves, are best added in fall to allow for decomposition before spring planting.
Organic mulch is a good way to mitigate soil moisture and temperature extremes. Studies show soil remains more moister cooler beneath organic mulch. In contrast, soil tends to become abnormally dry and hotter beneath landscape fabric and rocks.
Soil compaction occurs when mineral particles are compressed and pore spaces are made smaller. This restricts root growth, movement of oxygen into soil, and infiltration of water and fertilizer into soil.
To prevent compaction, avoid walking on or working in wet soils and use a layer of coarse organic mulch to buffer irrigation and rain drops and foot traffic.
Along with increasing organic matter and avoiding compaction, water and fertilize correctly. Too wet of soil reduces soil oxygen and inhibits soil microorganisms.
Source: Kelly Feehan, Extension Educator, Platte County
