Explaining mulch and amendments

Two gardening terms that can often be confusing are mulch and amendments.

Mulch is simply any product placed over the surface of the soil, to either cool down the soil or to warm the soil and at the same time conserve water. Amendments are added into the soil to improve the physical or chemical make-up of the soil. Another term is fertilizers which are used to add plant nutrients to the soil.

It becomes confusing because each type of product can have a secondary effect. For example, fertilizers are not considered soil amendments because they are basically adding nutrients to soil. Organic mulches can add nutrients to the soil and also improve the soil physical characteristics over a long period of time.

There are various types of amendments that you can use to start your garden. The first group of amendments is organic type amendments. Organic amendments increase the soil’s ability to hold water and nutrients. They also increase the biological activity of the soil, which results in more microorganisms and earthworms, which help improve the soil. However, not all organic amendments will qualify as a product that can be used for organic gardening.

Organic amendments also can improve the structure of the soil, which will improve the water-holding ability and drainage of the soil. Soil structure is the arrangement of sand, silt, and clay into small clusters. The smallest cluster is called a ped. Several peds may combine into a larger structure called an aggregate. Several aggregates may combine into a larger structure called a clod. Most of you are familiar with clods; you have probably thrown some in your lifetime.

The key to forming clusters is organic matter. Organic matter is often called the glue of the soil, because it forms organic bonds that ‘’glues’’ the sand silt and clay together.

As important as the structure of the particles (sand, silt and clay) is for the soil, the spaces between the particles are more important. When your soil has poor structure, the spaces or pores are very small. As structure improves, the total pore space stays the same, but the size of the pores increase. The larger the pore space the easier water and fertilizer can be absorbed by your soil.

Since organic matter is the glue of the soil, it is a very important component. If your soil lacks organic matter, it cannot form peds. The clay particles move towards the soil surface, followed by silt with sand on the bottom. With clay on the surface it forms a barrier that is hard for water to penetrate. Because of the clay surface many people feel they have clay soil, but in fact just have poor structure.

Here are some amendments that benefit the soil.

Manures can raise the pH of the soil, which is not desirable in the Antelope Valley. However, its ability to improve nutrient and water holding ability can offset the raising of the pH. It improves the soil permeability a little.

One of the biggest problems with manures is they can be high in salts and odors. The more the manure is composted or aged, the better the manure is for your soil. If you have fresh manure, it will be high in weed seeds unless well processed.

Compost is made from organic wastes like grass clipping and weeds. Compost usually does not change the soil pH but is a great amendment to improve soil life and soil structure.

Fir bark usually does not change soil pH. Fir bark resists compaction, which helps keep your soil loose. But fir bark does not increase nutrients and water holding as much as other organic amendments. It is best to add nitrogen fertilizer to the fir bark or by fir bark that has been nitrified. Fir bark can be purchased in bulk making it very reasonable to purchase.

Peat moss is commonly recommended in gardening books. It lowers soil pH and increases the water- and nutrient-holding ability more than any other organic material. Peat moss can be very hard to wet once it has dried out. Peat moss is also a very expensive soil amendment and is not usually used on a large scale.

All of these organic materials have advantages and disadvantages. I normally recommend the best one to use is the type that is the most economical, because to help your soil you need to add a couple inches to your soil and rototill it in order to change your soil.

The second group of soil amendments are not organic, but mineral in nature. Mineral amendments can also provide nutrients to your soil.

Soil Sulfur is the first mineral soil amendment, which is used to lower the pH of the soil. Although soil sulfur will probably not lower our soil pH over the long run it provides needed sulfur to the soil and can affect the soil chemistry and structure in some other beneficial ways.

Gypsum is another common mineral soil amendment. Gypsum is often confused regarding its use. Gypsum can improve soil structure if the problem is caused by high levels of sodium in the soil. High levels of sodium in the soil is a common problem in the Antelope Valley.

Limestone is a common mineral soil amendment that is not desired; in fact, it is detrimental to the soil. Limestone raises the pH of the soil, which is not needed in the Antelope Valley. Limestone also includes bonemeal. Since limestone is primarily calcium, the only times we see a calcium deficiency in plants in the Antelope Valley are when some plants are grown in containers. You can find tomatoes that show calcium deficiencies when planted in containers.