Environmental Benefits of Mulching and Composting
Introduction
Honda has long been recognized as a leader in the development and application of new technologies designed to reduce the environmental impact of its products through improved fuel efficiency and reduced emissions. The research that led to the introduction of the new HRX™ lawnmower line is in keeping with the Honda tradition of technological and environmental leadership.
The unique Versamow™ System of the HRX™ allows the user to select bagging, mulching or any combination of the two configurations by simply rotating a lever called the Clip Director™. Whether the user chooses to mulch or to compost or bag the clippings, all of the options provided by the HRX are better for the environment than conventional disposal of clippings.
Because the HRX forces clippings into the blade to be cut into smaller sizes, it significantly decreases the overall volume of grass clippings collected over conventional mowers. In the bagging mode, the user can mow 40 percent more turfgrass before the bag is full and empty the bag 40 percent less often than with conventional mowers. If the user disposes of the clippings, it reduces the volume of yard waste in landfills. If the user composts the bagged clippings, the smaller clippings will decompose more quickly. Both options reduce the environmental impact of the grass clippings. In the mulching mode, the HRX allows the user to recycle the finely cut clippings into the turf while still producing the clean, manicured look of bagging. And in any of the combination bagging/mulching modes, the HRX™ user can select the optimal degree of bagging and mulching with the mere rotation of the Clip Director™.
Mulching
Mulching usually consists of leaves, straw, peat moss or other natural materials that are spread on the ground around plants or over a newly seeded turf area to prevent evaporation of water and erosion of soil.
In the case of mulching lawn mowers, the mulch consists of grass clippings from the mowed turfgrass, which are cut into fine pieces that fall easily to the soil surface. There, they can be rapidly broken down by soil microorganisms, which release nutrients from the mulched plant material back into the soil.
According to Dr. Keith J. Karnok, (see Dr. Karnok's bio on page 25 of this tab) an agronomist and turf specialist with the University of Georgia, "It's a good idea to mulch grass clippings when possible, providing the mulched clippings do not interfere with the use or appearance of the turf area."
Some people may be reluctant to mulch grass clippings because the clippings form unsightly clumps which, when left on the surface of the turfgrass, also can damage the plant underneath. "The key to mulching grass clippings is the size of the clippings: the smaller the clippings, the better," said Dr. Karnok. Smaller clippings, of the size produced by the Honda HRX, fall more rapidly to the soil surface and cause less disruption to the appearance of the turf area. Mulching enhances the health and growth of the turf by reducing evaporation of moisture from the lawn and keeping soil temperature cooler. In addition, it has been estimated that mulched clippings, which are 85 percent water and five percent nitrogen, can provide up to 25 percent of fertilizer needs for an average lawn.
Some people may be reluctant to mulch grass clippings because they do not want to promote the buildup of thatch, an intermingled organic layer of dead and living shoots, stems, and roots of grasses that develops between the green vegetation of the turfgrass and the soil surface. Thatch is formed when the roots, stems, leaves and other parts of the plant are sloughed faster than they decompose.
"Contrary to popular belief, mulching grass clippings does not contribute to the buildup of thatch," said Dr. Karnok. "In general, proper mowing, irrigation and proper fertilization, and in particular, avoiding over-fertilization, will help keep thatch accumulation down." Certain turfgrasses accumulate thatch more than others. Creeping or spreading type grasses such as Kentucky bluegrass and Bermudagrass accumulate thatch faster than bunch type grasses like tall fescue and perennial ryegrass. If an excessive accumulation of thatch does occur, most equipment rental businesses have de-thatching machines available for short-term rentals.
In addition to the environmental benefits provided to the turfgrass itself, the practice of mulching grass clippings diverts valuable recyclable grass clippings from landfills, thereby reducing the volume of waste and helping extend the life of these sites.
It also saves money for the homeowner in municipalities that charge extra fees to landfill yard waste.
According to Organic Materials Management Strategies, a document published by the Environmental Protection Agency, yard trimmings make up approximately 13 percent (or 28 million tons) of the national waste stream, with grass clippings accounting for two thirds of all yard waste.
A growing number of municipalities, including Dallas, Texas and Niles, Illinois, and several counties in metro Atlanta, Georgia, charge homeowners a fee for special stickers to be applied to trash bags containing yard waste or require homeowners to purchase special yard waste bags. Others, such as Newfield, New Jersey; Glen Cove, New York; Huntington Woods, Michigan and Windsor, Connecticut, have stopped collecting grass clippings entirely, leaving homeowners no option but to mulch or compost.
Bagging
In its full bagging mode or combined mulching/bagging mode, the Honda HRX captures finely chopped turfgrass clippings that can be landfilled or composted. Since the mower clips the grass into finer particles than conventional mowers, it increases distance that can be mowed per bag while reducing the number of bags of clippings.
Composting
Composting is the process by which organic materials such as leaves, grass clippings, and other degradable home and yard wastes are converted into compost, a material useful for amending the soil. Through bacterial and fungal decomposition, composting breaks down these organic materials into a product that enhances the soil by increasing the availability of essential minerals, such as potassium and phosphorous, to growing plants and reducing the competition for nitrogen. When compost, a brown, crumbly, earthy material, is mixed into soil, it also improves the physical properties such as friability, infiltration, drainage and water-holding capacity.
While mulch, or uncomposted material, is placed on the surface of the soil, compost is mixed in with the soil, providing a healthy balance of soil amendment and plant protection. Uncomposted mulch should not be used as compost, because the decomposition process will impede plant health by robbing growing plants of nitrogen.
Composting usually is performed in a carefully constructed and maintained compost pile that allows the organic material to decompose as quickly as possible. Because the speed of decomposition depends on the level of microbial activity in the pile, anything that slows or halts microbial growth slows or halts the composting process. In addition, aeration, moisture, particle size, temperature and nutrient levels in the compost pile affect the speed of decomposition of compost:
- Aeration introduces oxygen into the compost process. The pile can be aerated by manually turning it once or twice a month. Aeration also should be maintained by mixing materials to keep them from compacting.
- Adequate moisture is necessary to maintain decomposition. In the absence of rain, the compost pile can be watered manually to maintain a level of dampness. Over-watering can slow decomposition.
- The particle size of composted materials helps determine the speed of decomposition. Smaller particles will decompose more quickly than larger particles. This is where the Honda HRX helps speed composting of grass clippings: smaller clippings will decompose more rapidly than larger clippings. Clippings should be mixed with other yard refuse to keep them from compacting and restricting airflow in the pile.
- A well mixed, adequately working compost pile should heat to temperatures between 110oF and 160oF as the microbes actively feed on the organic materials. These high temperatures also will help destroy weed seeds and disease organisms in the pile.
The carbon/nitrogen (C/N) ratio will affect the speed of decomposition. This means that the nutrients in the compost heap should be in the right proportions for proper decomposition. The ideal carbon-to-nitrogen ratio (C/N) is 30:1. When the decomposing organisms do not have the proper ratio of carbon, the organisms may lose nitrogen to the atmosphere as ammonia. On the other hand, if the initial carbon ratio is too high, the process will slow down and become very inefficient. For example, grass clippings have a C/N ratio of 19:1, kitchen wastes have a C/N ratio of 15:1, leaves have a C/N ratio of 60:1, and sawdust has a C/N ratio of 500:1. A gardener and composter can blend materials in the pile and add supplements, such as high-nitrogen fertilizer or blood meal, to achieve a proper C/N ratio.
Yard wastes that can be composted include leaves, grass clippings, straw, plant trimmings, twigs and small branches. Kitchen wastes such as vegetable scraps, coffee grounds and eggshells also may be composted. However, organic materials such as human or pet feces, meat, bones, grease, whole eggs and dairy products should not be used to make compost because they may pose a health hazard, cause odors or attract pests. Also, composting weedy or diseased plants may cause problems in the garden later if the compost pile has not reached the required temperature to kill these plants or seeds.
Compost piles should be no taller than five feet in height, and can be constructed from a variety of materials, including chicken wire or containers made of plastic, metal or wood. The container and style and method of composting will determine the speed of decomposition and availability of useable compost.
A pile should be constructed as follows, with each level being dampened thoroughly as it is added:
The bottom layer should consist of coarser materials, which will decompose faster on the bottom and allow air circulation.
The second level contains about 10 inches of organic wastes such as grass clippings and leaves.
The third level should consist of about one inch of soil or finished compost to help reduce leaching of mineral nutrients, such as potassium, released during decomposition.
The fourth layer should consist of nitrogen-rich material, such as grass clippings or nitrogen fertilizer.
In the next layers, the placement of organic wastes, soil and nitrogen-rich materials is repeated until the pile almost reaches the desired height.
The top layer should contain about five inches of straw or hay, and be concave to capture rainwater.
The pile should be turned manually about once a month to maintain aeration and a proper mixture of nutrients. The compost is ready when the pile has reduced in size by about half and the material is brown, crumbly, and fragrant with a clean, earthy smell.
