Soil Organic Matter in the Garden—With What?
Increasing the organic matter content of our soils is a permanent goal of gardeners and farmers alike. Let me state it more strongly: If I could do only one thing to improve the quality of my garden soil, it would be to increase the quantity of organic matter present. That single activity will help me in myriad ways in my garden. Over the next couple of weeks, we will discuss organic matter—how it improves soil biology, chemistry, and structure; the different kinds that exist; composting; etc. Today we will discuss how we can apply organic matter.
Adequate levels of organic matter in the soil improve the growth and health of plants through the retention and then release of nutrients, increase the absorption and retention of water to mitigate drought stress, promote the aggregation of soil particulates to improve drainage and reduce erosion, reduce compaction of soils, and possibly the most importantly, support a beneficial soil population of all types of organisms. In fact, with few exceptions, it is difficult to apply too much well-decomposed organic matter.
In our home gardens we can increase our organic matter in several ways. This can be as simple as purchasing bagged or bulk compost from our local nursery, the collection and application of leaves from our yards and gardens, the application of animal manures from nearby farms or neighbors, or as complex and thorough as composting yard and kitchen wastes. (And even composting is not particularly complex or daunting. We will discuss it in an upcoming column). In any case, decomposed leaves, branches, garden or animal wastes, or kitchen scraps add nutrients and soil life back into the soil.
It is important to distinguish that mature compost is the result of the entire process of decomposition of plant and animal materials. While it is possible to apply freshly fallen leaves, freshly cut grass, spoiled hay, raw manure, and even animal bedding to the garden, these will still have to decompose before many of their positive benefits can be utilized, and they may, in fact, be damaging to your garden plants in the form of high salts, residual pesticides, alkaloids (like tannins), nutrient immobilization, and so forth. As such, if you wish to apply raw organic material to the garden, be sure to allow sufficient time for it to decompose before adding your flowers or vegetables.
The same can be said for organic mulches of bark, pine needles, etc. These materials are not decomposed, and their purpose is to provide a uniform, attractive soil surface, as well as to conserve soil moisture and reduce weed growth. And while all of these characteristics are desirable and good, the microbes in the soil will also begin to decompose these materials and in so doing, they will "tie up" or immobilize the nutrients in the soil, making these unavailable to the plants. Accordingly, if you use a surface mulch, you should consider applying an additional quantity of nitrogen to the soil to account for the quantity that is immobilized.
One additional means of increasing the quantity of organic matter in your garden: growing "green manure". Green manures are plants that are grown specifically for the purpose of incorporating them back into the garden to feed the soil. They can be grown during an existing crop (in the understory), after your main harvest but before a frost, in the fall for spring growth, or it can even be grown on a different area of the garden for later application into your main garden area. In any case, this plant material is cut and turned into the soil where it can decompose. After it decomposes it will have enriched the soil and added valuable nutrients which can benefit future crops.
Any of these methods may be used to increase the organic matter in our soil. And let us say it again: If there were only one activity that I could do to improve my garden soil, it would be to add abundant quantities of high-quality organic matter. In the coming weeks we'll see how.
Send your soil organic matter questions to info@meadowview.com and we'll work together to help you improve your garden soil
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