A Question of Mulch

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Mulch has become a controversial topic. While mulching around established plants is recommended to reduce weed growth and retain moisture as well as improve the appearance of the planting beds, there are many products to choose from. There are concerns about available products, additives and sustainable sources. This article will touch on the various issues regarding mulch.

Rocks/Gravel

Rocks and gravel are sometimes used as decorative ground cover and for paths and patios however, I personally don’t regard them as mulch. They eventually move down into the soil and make digging difficult, so they are not appropriate for beds where regular planting is done. Excavation of the rocks, gravel and soil and replacement of topsoil is required return the area to planting bed condition. 

Rubber Mulch

Rubber mulch is made from recycled tires and seems at first glance to be a good candidate for recycling old tires. Rubber crumb mulch has been proven to reduce compaction when used as a soil amendment on sports fields. It is used in playgrounds around trees and places where the soil is not regularly disturbed. It comes in attractive colors and decomposes less quickly than organic products, which makes it an attractive product. In planting beds where soil is regularly disturbed, the mulch will more quickly become incorporated into the soil.

While long lasting, rubber mulch does eventually decompose. As it does, it releases toxic compounds into the soil, affecting plants and aquatic life. Some of the compounds leached into the soil can even be harmful to humans. If incorporated into the soil, it will not add to the ecosystem that supports plants and will be very difficult and expensive to remove.

Issues of increasing soil temperatures have been documented and there has been some controversy about the effect of increased temperatures on plants. In addition, rubber mulch is extremely flammable and difficult to extinguish.

Cypress Mulch

Cypress mulch is an organic product that has a reputation for being superior to hardwood or pine mulches. Studies in Florida, a major source for cypress mulch, do not support this claim. Controversy surrounds the sustainability of harvesting cypress and has produced enormous pressure to curtail its use. Wal-Mart was concerned enough to remove cypress mulch harvested in Louisiana from their inventory. 

Other Commercial Organic Mulches

Wood mulches that originate from by-products of a responsible timber industry qualify as sustainable. Forestry has adopted better stewardship practices and much of the industry recognizes the value of taking care of plants, wildlife, soil, and water and air quality. To the extent that sustainable methods are used in producing wood mulch, it is an ecologically sound product. Mulch colored with chemical dyes adds inorganic compounds.

Wood mulches require nitrogen to decompose and ‘steal’ nitrogen from surrounding plants to some extent. This is why mulch is not incorporated into the soil or around the base of seedlings. Trees, shrubs and larger plants can be mulched without harm to them.  If the wood chips or mulch smells sour, water it to leach out the toxic compounds (be sure the water doesn’t get on your plants), turn the mulch and wait a few days for it to detoxify before mulching your plants.

Wood chips are available from many city or community agencies. These chips are usually coarse and good for paths and playgrounds. Putting them through another round of chipping is recommended if using them on planting beds. High variability in the quality of the chips has been reported.

 If you purchase wood chips or mulch locally from a sawmill, be sure to determine that it does not contain walnut, which releases chemical toxic to plants.

Hay is a popular mulch for vegetable gardens. It is inexpensive and sustainable if locally sourced. Hay and straw sometimes contain weed seeds.

Check the MELA website http://www.melaweb.org/com-products.html for sources of mulch and other products.

Making Your Own

Of course the most sustainable method for producing organic mulch is to put yard waste through a chipper and use it as mulch on planting beds. There is no transportation, you control the quality and you are recycling in the best possible way without the need to compost. When compared the cost of commercial mulch, the cost of a chipper, over its useful life, becomes more attractive. 

Be sure not to put weeds or yard waste from plants infested with insects or diseases into your mulch to prevent spreading the problem. High heat compost of weeds will kill weed seeds if you want to recycle them. 

Summary

In summary, organic mulches are better for your soil than inorganic mulches. They supply valuable organic matter to your soil to improve its structure and nutrients. 

Posted on May 18, 2014 .