Month: August 1999

This title appeared in a New York Times article of August 1998. 1 filed it for future reference. When I finally read it I was surprised to find that it did not discuss what I imagined would be there. Instead it started out discussing global warming and carbon dioxide. According to Dr. Tyler Volk, a biology professor at New York University the earth’s soil contributes 10 times more carbon dioxide to the atmosphere than all human activity. We all know from reading that there are beneficial forms of life in the soil but never would we have imagined that their contribution to the atmosphere as a result of the life processes of microorganisms, fungi, worms, bugs, etc., would be so large.

Apart from this aspect it was even more unexpected to come across the statement that gardening may be harmful to the Earth since tillage releases carbon dioxide. Most gardeners assume that a plow, shovel or rototiller is required for a good crop. This raises the question: why do we use cultivation in our gardening? The answer, when one thinks about it is to create a zone where domesticated crops have little competition from other plants. In the past the increase of carbon dioxide produced by small scale tillage was absorbed by plants carrying out photosynthesis. However tillage now is carried on at such a scale that it has become a large contributor to the surplus of carbon dioxide in the atmosphere. So when soil is stripped of its natural cover in order to grow crops, a significant amount of its stored carbon, which contributes to fertility, is lost as carbon dioxide.

Another aspect is that cultivation and compaction destroy beneficial soil fungi. Along this line the beneficial fungi have been increasingly brought to our attention over the past few years. Thus we see articles of vesicular arbuscular mycorrhizae and their beneficial effects.

Gardeners can compensate for the tillage-induced loss of carbon by adding compost and manure, and they can minimize the loss of carbon dioxide from their gardens by experimenting with “no till” gardening. This may be successfully accomplished with a variety of methods, such as: sheet composting (thin layers of compostable materials spread on the soil like a thick mulch) or planting soil improving crops like fava beans or vetch.

Another method mentioned in the article, was to use a deep (I foot) mulch, Assuming this was not a misprint, this method illustrates the dichotomy between a theoretical approach and a practical one which would not violate the theme of the original article-“Do No Harm”. One of the basic tenets of gardening, or most anything for that matter, is to avoid overdoing something. Depending on the material used, the recommended depth of mulch ranges from I to 4 inches, with 2-3 inches being most common for organic material. Deeper than that is asking for trouble, considering all the variables plus the likelihood of attracting undesirable wildlife.

Uncomposted material has a high carbon/nitrogen ratio. Since soil microorganisms require nitrogen in order to decompose the wood, they will deplete the soil of nitrogen, resulting in poor plant performance. Thus, a gardener may have good intentions of conserving water and keeping weed growth down, but by using excess mulch and improper materials, he or she can invite disaster.

In my fields, I have practiced mulching for many years and have become a believer in its benefits. I have found that it keeps the soil moist and friable, uniform in temperature, and easy to work. It also helps keep the rain from splashing mud on plants, the ground moisture from evaporating, and weeds from growing. Every garden needs a little mulch.

Mulch is a layer of material, organic or inorganic, spread on the ground near plants or in the aisles. It protects the soil from the effects of the wind, rain, and the hot sun. During a long dry spell, I get by with a lot less watering. Mulch moderates the soil temperature keeping it a little cooler in summer and warmer in winter. The best part is that it cuts down on the time spent on garden upkeep.

Materials Used

Any number of materials are used for mulch – grass clippings, paper, straw, sawdust, or polyethylene black plastic film. I prefer to use organic materials because they can be incorporated in the soil after the growing season, thus adding valuable nutrients.

• Grass clippings are one of the best and most commonly used mulches. When they decompose, they leave nitrogen in the soil. Clippings must be left to dry for a day or two by spreading them in the sun before they are used. If they are fresh and moist they will mat and rot, becoming slimy and foul smelling.

• Newspaper is great when used under other mulches. Never use newspaper by itself because it acts as a wick and pulls moisture from the soil. I place four sheets of newspaper (black print only; colored print has toxins in it) on the area I want to mulch. I then spread the grass clippings or straw on top, covering the paper completely. When paper is used, only two or three inches of an other material are placed on top. Huge quantities of mulching material are not needed. Newspaper, used with a mulch, is also good because the paper will block weeds from coming up through the mulch. Any seeds in the mulch material will not go down into the soil to sprout.

• Straw is a good mulch, but weed seeds may come with it. This is why paper under the straw will save a lot of headaches. Avoid hay as mulch — usually it brings weed problems.

• Sawdust is an excellent mulch, but must be partially decomposed before applying. Otherwise it will deplete the soil of nutrients as it breaks down. If fresh sawdust is used, apply extra nitrogen to the soil under the sawdust. I use newspaper instead of nitrogen under the fresh sawdust.

• Black plastic does not build the soil or contribute nutrients, but it does deter weeds and conserves moisture. Rain does not penetrate this material, so drip irrigation must be placed under it. A problem with black plastic is that it tends to absorb the heat of the sun and raise the soil temperature – sometimes very high. A layer of straw or grass clippings on top of the plastic will help.

The initial cost of these mulches is offset by the fact that they can be recycled from year to year.

Special Benefits of Mulch:

• Insect Barrier – Some insects, including the Colorado potato beetle, striped cucumber beetle and spotted cucumber beetle, will avoid a mulch of straw.

• Water Conservation – Many times conserving water will be as important as watering the crops. During July or August dry spells, make sure the garden loses as little water as possible. Mulching helps protect bare soil from evaporation.

• Erosion – A layer of mulch will protect your soil from rain that causes erosion.

• Weeding – Mulching prevents weeds from growing. Weeds need light to grow and mulch shades out the light.

Do’s and Dont’s of Mulching

1. Mulching too early in the spring keeps the soil from warming up and encourages rot during excessively wet periods.

2. Wait until the soil has warmed up in the late Spring, then put mulch on the spring crops. This will help to delay bolting.

3. Mulch the summer crops late in June when the soil has warmed and will continue to remain warm. This prevents the soil from becoming hot and dry. Mulching will keep the soil at an even temperature around the plant roots.

4. Leave a gap between mulch and plant stems for air circulation.

5. The best time to mulch is right after a rain.

6. If the mulch is left on over the winter, it will encourage earthworms and beneficial microorganisms. They will eventually devour the organic mulch and turn it into good humus

At the end of the season, when the mulch is turned into the soil, it will be broken down and continue to enrich the soil’s humus content.