Ruth Stout, garden writer of the 1960s and 70s made mulch famous. Her material was published by almost every gardening magazine and to this day a web search on her name will yield a lot of hits. But there are not many real world examples of market gardeners using her famous “no work” method. Further on in this section, I’ll address the problems with permanent mulch and how to get around them.

The mulch is permanent in the sense that it is reapplied with almost every crop. I use grass clippings on my beds almost exclusively, along of course, with the remains of previous crops. The clippings are presently delivered free by a commercial landscape gardener year around at an average rate of 2 cubic yards/meters of fresh clippings per week and most of that is applied to about one-half acre of bed surface. The mulch is applied about 2 inches (5cm) deep and settles down to about half that depth. When I find I have more than I need for the beds, the extra clippings go on the alleys between the beds at about half that rate where they mix with crop residues removed from the beds and eventually get reapplied as the beds continue to be built up over time.

The main values of mulch follow:

1. To a large degree mulch substitutes for tillage in that weeds are controlled, particularly annual weeds. Perennial weeds can be much more difficult and are best controlled with glyphosate herbicide, the active ingredient in RoundUp but now sold generically. Perennial weeds can also be smothered out with carpet or black plastic but infested areas will need to be taken out of production for at least the time it takes to grow a crop. Hand pulling weeds that grow in the very open soil under mulch is relatively easy and all weeds can be controlled by hand with sufficient diligence.

2. Mulch also does the job people think they do when they till, namely, opening up the soil for water, root growth and a limited amount of air. Earthworms and other soil macro-life feed on it and open passages deep into the soil. These passages, along with the passages created by the decaying roots of previous crops, leave soil open and friable to a degree that is quite amazing. On a limited basis, I can dig holes for transplanting with my bare hands but I would not like to do very much of it.

3. To a large degree mulch substitutes for applications of industrial fertilizers and, unlike most of these fertilizers, mulch contains all the elements plants get from the soil that they need for good growth. But mulching with straw alone is sure to fail because it’s almost devoid of nutrients, particularly nitrogen, and will deplete the soil of nitrogen available for the crops (a new research finding that contradicts previously held opinions including my own). Also, mulch can only build soil organic matter if it contains sufficient nitrogen. The composition of stable soil organic matter requires specific ratios of carbon to nitrogen. If carbon is in excess it is oxidized by microorganisms and lost to the atmosphere where it contributes to global warming. The best mulch material is cut green before it has a chance to go to seed. If I had to buy it, I’d use alfalfa hay. Stable soil organic matter, humus, will build up very rapidly under permanent mulch but if sufficient nitrogen is not available, crops will suffer. This is because the build up of organic matter will get first call on the nitrogen until at least the original, natural percentage of organic matter in that soil is reached.

4. The buildup of stable organic matter under mulch, as described above, sequesters the atmospheric carbon that is leading to global warming. The potential of soil for absorbing carbon may be humankind’s best opportunity to mitigate global warming. As long as tillage agriculture remains the preferred way of producing crops, this potential will never be realized. In the terminology of systems, soil is a carbon sink.

5. The permanent mulch cover also serves to shade the soil from water loss by evaporation, especially during the period that begins after transplanting into the bed and before a canopy of foliage develops. During this window of time a farmer may need to apply a hundred times as much water as the new plants required in their original flats because of evaporation loss from bare soil. Globally, whole continents are being pumped dry by agriculture. It is incumbent on any gardener or farmer interested in sustainability to produce crops with the most prudent use of water. Mulch is one of the very best tools for doing this.