Yesterday, I had a conversation with someone while dropping off some compost. That person was concerned about the productivity of the garden and its relationship to the soil. We looked at some garden beds and saw a typical situation. The plants are alive and look reasonably healthy, but the soil does not look the same. The bed (4’ x 10’) has the typical structure of about ½” of mulch on top, then about 1-2” of a sandy compost mix, and then soil. When I dig into the soil, it is compacted and tough to dig through. I don’t see any signs of soil life such as worms, worm holes or little bugs crawling around. I don’t see any signs of decaying organic matter. That means the important things of nutrient cycling, carbon cycling, water cycling/holding are weak or maybe not happening at all.
An ideal soil has a lot going on. It is dynamic like our bodies. It is a living thing. Think of it like your spouse – beautiful and a mind/system of its own. Ideally, it would be 25% air, 25% water and 50% soil composed of living things, decaying food scraps, minerals, old soil and mulch in a 3-4” band across the top of the soil, and preferably deeper.
In his new book, Organic Management for the Professional — Howard Garret of Dallas, Texas’ top organic gardener is recommending 4-6” of mulch on top. Think of mulch as SPF cream or moisturizer. In a region that evaporates 2-3x more moisture than we receive in rainfall (excl. dew/humidity) as compared to regions in the USA that evaporate 0.5x their rainfall (coastal forest areas), we need to capture and hold as much moisture from the dry hot winds, and high UV as possible. Mulch keeps your soil alive at the upper soil levels by preventing the UV from reaching the soil. More importantly, it sequesters the moisture down low where the hot dehydrating air cannot pick it up and carry it off.
The answer at the end of the conversation was not to add more compost, but to turn the top layers of the mulch into the compost. Make the mix fluffier instead of so dense. Next we will try to get more life working in the soil as well as look at minerals/nutrients. Before the end of the fall season, I hope to add more mulch on top of the soil to prepare it for winter.