How Grass Grows

The best way to create and maintain a healthy lawn is to understand how the grasses that make up your lawn grow. Basically, water and nutrients are absorbed into the root system and pulled up into the green blades of grass by photosynthesis. Photosynthesis is a plant process that uses water and energy from the sun to convert carbon dioxide into carbohydrates that it uses for growth and other plant functions.

A natural soil environment teems with bacteria, fungus, nematodes, earthworms, and other soil organisms. Many of these soil organisms break down grass cuttings and other materials into humus that enriches the soil. Other soil organisms form symbiotic relationships with grass and other plants. A symbiotic relationship is a relationship that is beneficial to all participants in the relationship. Plants, including grasses, release exudates from their roots that attract beneficial organisms. In other words, plants help to create their own soil environment.

Beneficial soil organisms, which are found in natural humus and compost, make minerals available to your grass. They also help protect grass and other plants from predatory life forms. Unfortunately, herbicides, pesticides, and chemical fertilizers destroy these soil life forms. Your grass becomes weak and is easily attacked by soil pathogens. Understanding more about soil environment will make the importance of soil life forms even clearer. It will also make you a believer in organic lawns.

Soil Environment

A healthy soil environment is dependant on a combination of factors including structure, mineral content, pH, and decomposing bioforms.

Soil Structure

The three basic types of soil are sand, clay, and silt. Sandy soil is easy to work with and drains quickly, but dries too quickly. Clay is heavy, hard to work with, and drains slowly. Silt drains fairly well and is workable when wet, but very hard when dry. In addition to the three basic structures, soil usually contains varying amounts of rock.

Most soil is a composite and contains too much sand, silt, rock, or clay to be satisfactory for your lawn. In addition, soil organisms may have been scraped away with the topsoil when your lot was graded, or the pH may not be compatible with your lawn grasses.

PH is an important part of soil composition and affects the plants and soil organisms that can live in a particular soil.

Soil pH

Most lawn grasses grow well with a soil pH of 6 to 7. pH is a measure of acid-base balance and uses a scale of 1 to 14. 1 is extremely acid; 7 is neutral; and 14 is extremely basic (alkaline). Few grasses will grow in a pH that is too acid or too alkaline.

A pH of 6.5 is the point where nitrogen, phosphorous, and potassium (N-P-K) and trace minerals are most easily available to grass and other plants. Arid regions tend to have alkaline soils and regions with heavy rainfall tend to have acidic soils.

If your lawn looks like it is missing an element such as iron, the real problem may be that the pH is too far away from 6.5 for the grass to absorb it. You can find out by testing the soil pH of your lawn. Inexpensive test kits are available at most garden centers. If your soil is out of the correct pH range, you can change it. This is where the magic of soil biology creates miracles.

Magical Decomposition

Grass, leaves, broken branches, and dead animals fall to the ground and are eventually decomposed by fungus, bacteria, nematodes, earthworms, and other life forms. The rich material that remains is called humus. Humus is the best remedy for all soils. The multitude of soil life makes more minerals available, and available in a wider pH range, than otherwise possible. It also makes an ideal environment for symbiotic relationships.

Now let’s take a closer look at how grass grows.

Photosynthesis

Photosynthesis uses the sun’s energy and water to convert carbon dioxide into carbohydrates and simple sugars. The byproduct of photosynthesis is oxygen. Water (H2O) plus carbon dioxide (CO2) becomes carbohydrate or glucose (the exact chemical composition depends on the kind of grass or other plant) plus oxygen (O).

The secret of photosynthesis is chlorophyll, which is stored in chloroplasts in grass blades. During photosynthesis, the sun’s rays are absorbed by chlorophyll and used to create simple sugars and carbohydrates. Healthy grass is green because green is the only part of the color spectrum that grass reflects. Grass absorbs all other colors.

Before photosynthesis can take place, the roots must pull water and minerals up from the soil to the blades of grass in your lawn. This pumping process is called transpiration. Chlorophyll in leaves absorbs the sun’s energy. Pores on the underside of grass blades absorb carbon dioxide while allowing oxygen and water vapor to exit. Photosynthesis uses the water and minerals pulled up by transpiration, plus carbon dioxide from the air, to create carbohydrates, simple sugars, and other plant necessities.

The efficiency of photosynthesis depends on soil organisms just as much it depends on the sun. Exudates, chemicals that ooze from grass and plant roots, attract beneficial fungi and bacterium. Mycorrhizae is one of the most important beneficial fungi and Rhizobium is one of the most important beneficial bacterium.

Mycorrhizae

Mycorrhizae attaches itself to grass root hairs and uses a small amount of carbohydrate energy from the grass to extend its own root system. The mycorrhizae root system more than makes up for the energy it uses by making minerals more available to the grass. In addition, healthy mycorrhizae root systems expand and interconnect with the roots of other kinds of grass, plants, and even trees. Mycorrhizae root systems help to add beneficial structure to the soil and make your yard into one continuous soil system. A plant relationship with mycorrhizae is referred to as symbiotic—it is helpful to both host and intruder.

Rhizobium

Ryegrass is often part of commercial grass seed mix and is an excellent addition to your lawn. Ryegrass is one of the plants that can ‘fix’ nitrogen (make nitrogen available to its roots and other nearby roots).

Although atmospheric nitrogen (N2) makes up nearly 80% of our air, grass and other plants cannot use nitrogen in the N2 form. N2 is considered an inert gas because it is very stable—it is composed of two nitrogen molecules that are held together by a triple bond. Grass and other plants need ammonia, which is nitrogen combined with hydrogen (NH3), in order to manufacture amino acids, proteins, and other essentials. However, they are unable to break the N2 bond without help.

Ryegrass and rhizobium bacteria have a symbiotic relationship. Rhizobium bacteria is attracted by ryegrass root exudates. Rhizobium bacteria attaches itself to ryegrass roots and absorbs both nitrogen and hydrogen (NH2) from air in the soil and uses some energy from the grass (carbohydrates) to change the nitrogen and hydrogen to ammonia (NH3). The grass absorbs the NH3 and converts it to NH4 (ammonium nitrate). Ammonium nitrate is a fertilizer for your grass.

The rhizosphere is the moist area that extends approximately one millimeter around roots, root hairs, and mycorrhizae. It is teeming with microscopic life forms that are both beneficial and pathogenic. As long as the plant is healthy and the correct balance of air, water, pH, and other factors is maintained, the plant’s natural defenses keep out pathogens. But once the natural balance is disturbed, the root system is disrupted and pathogens can get a foothold.

The best to way keep pathogens away is to ensure a healthy soil environment for your lawn and other plants. Chemical fertilizers, herbicides, and pesticides destroy the natural soil environment and open the door to pathogens.

Compost

If you want a yard that is healthy, alive, vibrant, and free of chemicals, learn about composting. The end result of compost is humus, which is nature’s own fertilizer. Compost adds structure to soil and acts as a natural buffer, which allows plants to absorb minerals in a much wider pH range. The microforms in compost also help to neutralize pH extremes. With the help of compost and proper watering, the grass, trees, and other plants in your yard will grow deep roots and have very little difficulty with the pests that menace other yards. To learn more about composting, visit the Guide to Composting.

Types of Lawn Grass

Grass types include summer annuals, winter annuals, and perennials. There aren’t any biennial grasses. Annual grasses complete a life cycle each year. Perennial grasses continue to live year after year. However, most grasses, perennial or annual, will continue to grow if they are mowed.

Many lawns are mixtures of two or three different kinds of seeds. As an example, a typical plant mix contains tall fescue, Kentucky blue grass, and annual rye grass. This combination works well in many areas. Rye grass makes nitrogen available to the other two grasses. This enhances both Kentucky blue grass and tall fescue, both of which grow well in many different environments. The three grasses are good companions.

Lawn grasses are made up of stems, which are called culms. Culms grow from the crown, or base, of the plant and develop leaves. The lower part of the leaf is referred to as the sheath and the upper part is referred to as the blade.

Annual Grasses

Annual grasses complete a growing cycle each year. They reproduce by developing small flowers that produce spores. The spores pollinate other flowers, which produce seeds. The seeds produce a new crop the next year. This is called sexual reproduction.

When annual grasses are mowed, they still manage to re-grow because buds that are left on the lower portion of the stems grow back. This kind of re-growth is called aerial branching.

Examples of annual grasses are annual rye grass and annual bluegrass.

Perennial Grasses

Perennial Grasses reproduce both sexually and by another kind of reproduction, called vegetative reproduction.

Vegetative reproduction takes place when stems form horizontally within the soil or on top of it and reproduce a new plant. Horizontal stems that grow on top of the soil are called stolens and stems that grow horizontally within the soil are called Rhizones. The new plant receives energy from the original plant until it is strong enough to take care of itself.

Examples of perennial grasses are perennial rye, Kentucky bluegrass, and tall fescue.

Visit this page for a complete guide to different types of grasses.

I also recommend this Guide To Organic Lawn Care.

By creating healthy soil, you will create a happy lawn. Think Organic!