At a horticulture training a number of years ago, we visited a multi-generational family vegetable farm where the soils were not just well drained but “exquisitely” well drained. An agent who had long worked with them told a wonderfully instructive story. The old grandfather who had started the business was no longer driving because of poor vision, but he wanted to keep an eye on things so he had one of his sons ride him around for a daily inspection. One day he asked, “Why is the Sims field (farmers tend to give fields names, sometimes based on who had owned it originally or for a natural feature such as a soil type) so much greener than the Murray property?”
His son replied, “You know, Daddy, that’s where those Clemson people planted a cover crop last winter. The annual soil test showed that the organic matter content had risen from a half to 1 percent.”
That’s the power of organic matter. In South Carolina we have old, weathered soils, high rainfall, and increasingly warmer winter temperatures. Soils are primarily composed of three mineral fractions. The largest particles are sands, followed by silt, and then the smallest mineral component is clay. The relative amount of these minerals determines the soil texture. A loamy soil contains equal amounts of all three and the spaces in between those particles contain either air or water. Organic matter is the smallest solid portion of an overall unit of soil, and in our state that usually means between 1 to 2 percent, if you’re lucky. Compost is simply a form of organic matter that can be created by modern processes and added to specific sites where plants are grown.
Organic matter is mostly derived from decayed plant material, wood, stems, leaves, fruits, and roots. The deep and fertile soils of the Midwestern prairies got most of their organic matter from the huge amount of material shed by the roots of the tall prairie grasses. Microorganisms, amoebas, protozoa, fungi, and such, along with small invertebrates such as earthworms and termites, are decomposers, breaking down complex carbon-rich substances into compounds that plant roots can absorb. Most are aerobic, requiring oxygen, and are active when soils are warm and adequate moisture is present.
The Midwestern soils are frozen half the year, bringing a dead stop to organic matter decomposition until spring. In South Carolina, the decomposers are almost never inactive; it’s as if your son brought home half his fraternity for Thanksgiving and you had to feed them until Easter. Since our soils hardly ever freeze, we lose organic matter each year. One exception is bottom lands in the mountains, which are sought after for summer vegetable production. The high-water content fills spaces that would otherwise contain oxygen necessary for the decomposers to function rapidly.
Why is this miniscule portion of the soil so important? You can’t change your soil texture. Bringing in loads of sand or topsoil is not practical as it would take tons and tons to effectively alter more than a small garden plot. Also, you can’t rely on commercial topsoil. Because it is not regulated, it consists of whatever someone fills a truck with, and it often comes with weeds or other contaminants. What you can do, however, is add organic matter and be like the retired farmer, who even with limited eyesight saw the difference in soil fertility on the Sims plot after one year of cover cropping.
Adding the correct amount of organic matter to soil provides negative chemical charges that bind with and prevent the mostly positively charged nutrients from leaching out with water. This process also allows soil particles to form aggregates, which are discrete structures that allow for easier movement of microorganisms, plant roots, water, and air in the soil. We’ve all heard the phrase “water is the new oil,” and here is a critical fact to drive homeowners’ and farmers’ decisions about soil management and amendments: a 1 percent increase in organic matter content translates into an acre of land holding an extra 16,500 gallons of water within the plant root zone.
A little is good, but too much is not. An excess of organic matter holds too much water, can cause root rot, and reduces proper aeration. For containers, I use one part compost to five parts of potting soil. For plants that stay in pots for years, I simply top dress with compost every year. For a raised vegetable bed, stay with the ratio of one bag of compost well mixed with five of potting soil.
You can put on a mask, drive to the gardening center, and load up a 50-pound bag of compost. Or you can use this time of being home more to start making your own, and it’s much simpler than trying to get that sourdough starter mix just right. As far as helping the environment, how about the fact that yard and food waste accounts for 30 percent of what we send to landfills every year? Instead, you can turn most of it into one of nature’s most valuable products and avoid having it buried where it will add to the production of climate change promoting methane gas.
For at-home composting, start a compost pile in an area where you’ll have room to turn it. There are numerous ways to build structures or purchase fancy ones to hold yard trimmings and vegetable waste, but neither type is necessary. A simple pile on the ground that is small enough to turn once a week with a pitchfork is an easy way to get started. Just be sure you allow enough space to move the pile back and forth from one spot to the other. The trick for relatively fast breakdown of yard and vegetable debris is to get a proper ratio of carbon to nitrogen; one part nitrogen containing material (greens decompose quickly) to 30 parts carbon (browns, or the material that is slower to break down) is the proper mix to allow the decomposers to multiply and do their work. The pile should be moist but not soggy. Eventually it will decay. Composting has been taking place since plants first began growing on Earth. You can make composting a serious hobby involving thermometers and shredders or just keep it simple. For example, a friend of mine lived on a military base that did not allow composting, so she dug a small hole in the ground each evening and buried her leftover vegetable scraps and had a greener yard than the commander.
Leaves, twigs, newspaper (inks are now vegetable-dye based), shredded paper, cucumber and tomato peels, cut up cantaloupe rinds, cabbage cores, pecan shells, and more can all be added to a backyard compost pile. The smaller the material, the faster it will decompose. I visited a home where they raked magnolia leaves and then ran the lawn mower back and forth over them. They used this in a lovely pile of compost in a concrete block retaining structure, where they could turn it. You can add blood meal to help provide extra nitrogen to achieve the right carbon to nitrogen ratio if you have much paper, straw, or cardboard on hand.
Although grass clippings are a great source of nitrogen, it is better for turf to practice grass recycling, which involves simply letting cut grass fall back on the lawn. Keep mower blades sharp and do not cut off more than a third of the blade at any time. Cut grass when it is dry to avoid clumping. It is difficult for home composters to get temperatures hot enough to kill weed seeds. Leaving the clippings on the lawn will keep weed seeds out of the compost, and if you treat your grass with herbicides and/or insecticides you won’t introduce them into your compost. Commercial composters have carefully controlled conditions that generate temperatures that kill weeds and harmful bacteria, which is why they can use animal waste, fats, meat scraps, and such, but those are verboten to backyard practitioners of this art.
Several companies in South Carolina produce high quality compost for purchase, and many municipalities have composted yard debris available as well. Adding compost to the top of mulched flower beds is an effective way to add nutrients, including micronutrients, and improve soil texture at the same time. Avoid potentially burning synthetic fertilizers, which also tend to lower soil pH. You don’t have to rake away the mulch; the compost will work its way through and help decompose the mulch, which is what you want to happen. It’s an example of composting in place. Lightly top dressing your lawn will improve the growing conditions for that area, and improvements in soil aggregation can help prevent compaction.
Clemson Extension, of course, has information. Check out online the “Clemson HGIC Factsheet 1600, Composting,” which offers everything necessary about this perfectly natural process that is millions of years old. If you get fire ants in your compost, you can use a bait product containing hydramethylnon; watch Making It Grow Fire Ant Treatment on YouTube. Or visit the S.C. Department of Health and Environmental Control website and read its guide to this process: Composting — Simple Steps for Starting at Home – SCDHEC.
Since the garden club ladies who award the “Yard of the Month” sign speed up when they ride past my overwhelming 2.5 acre yard, I use the “Bed of the Month” method. Fifteen years ago, I planted an alley of small, i.e., affordable, Buxus harlandii shrubs bordering the path toward the back vegetable/flower garden, leaving gaps in the pairings as if it were a remnant from past years. At the end of the day, I take my kitchen vegetable scrap bucket, known affectionately as the “bouquet,” to that area and scatter the contents under the boxwoods in rotation. They’ve never been fertilized and are quite beautiful, and, when I use them for Christmas wreaths and flower arrangements, no one knows or cares that they have rotten tomato cores and crushed eggshells returning nutrients to nature under their spreading branches.