Is our title an oxymoron? It appears to be a contradiction. Actually, to grow and maintain health, soil needs tillage. It just doesn’t need to be done with steel, iron, or aluminum. Healthy soil needs lots of pore space; at least fifty percent of a soil’s volume should be open space to accommodate adequate air and water. Tillage with man-made tools can open pore space and temporarily increase water and air capacity. Unfortunately, this type of tillage does not create stability, and the space created tends to collapse quickly.
By contrast, in a no-till system, we use biology to do the tillage and create very stable pore space. The list of tillage tools in the no-till gardener’s toolbox (well, actually, the no-till gardener’s soil), is quite lengthy. Practically all biological life in the soil contributes to tillage. The pores created range from quite large to microscopic. At the larger end are big plant roots and nightcrawler tunnels. At the smaller end of our tillage tools are tunnels left by the movement of bacteria and fungal mycelium. The latter range in size from microscopic to large enough to easily see with unaided eyes.
Perhaps our title is an oxymoron, because biological tillage is less about breaking soil apart than it is about building soil structure. It’s less about tunneling through the sand, silt, clay, organic matter, and minerals that make up soil, and more about plants and microbes working together to build homes for the microbes, which in turn benefits the plant roots. We can arrive at this conclusion from the study of soil aggregation.
Simply put, aggregates are like small sturdy houses for microorganisms. Soil particles are formed into microaggregates and macroaggregates, which are the basis for soil structure. Microaggregates are formed when bacteria adhere to soil particles and organic matter. Macroaggregates are formed when fungi glue microaggregates together using glomalin, a sticky protein substance only fungi create.
The soil aggregates are a basic indicator of soil health. They are formed microbially and create stable open spaces within the soil. Macroaggregates are very visible and resemble small brown peas. By contrast, a soil that has been over-tilled (or, if it has been relatively dead microbially, even lightly tilled) will have a much finer texture resembling sugar.
While all this building activity is done by microbes, it is powered by plants. Much of the soil ecosystem is dependent on the energy of root exudates from living, growing plants. This is far from a passive process on the side of the plants. It has been recently discovered that plants can create unique combinations of exudates that are tailored for the specific microbial community they need at the precise time they need it. I understand this to mean that plants produce compounds that feed the species of biology that best make available the soil nutrition that they need for their next phase of growth and production.
That is pretty amazing! It’s hard to understand how researchers can discover such amazing designs built into creation and not give recognition to the Designer.
As a practical matter, we gardeners can help this process not only by avoiding the disturbance of our soil dwellers’ homes as much as possible, but also by providing as broad a diversity of plant species as practical. Since every species of plant is likely to support a little different profile of soil biology to maximize its own needs, more diversity within plant communities will support a broader range of biology. The result will be a healthier and more resilient soil.
It is most common in full-till gardening and farming to plant long rows of single species. When working with permanent raised beds and avoiding most mechanical tillage, this practice is seldom most desirable. Instead, we should take advantage of different plant growth characteristics and maximize solar capture, ground cover, and species diversity. This could be combinations of food crops, or possibly food crops grown together with flowers, or species grown just for their cover crop characteristics.
Here is one example of a combination that can work. You may have read about this one in your school social studies or history books. The Native Americans planted together the “three sisters”— corn, beans, and squash. These can still grow well together today. We can also use different variations of the same concept. Cucumbers do not mind partial shading and can grow well in this culture.
Companion planting doesn’t necessarily mean willy-nilly interplanting of the various species. We can keep things somewhat neat-looking and accessible. For example, in a 3-foot-wide raised bed, we can plant one row of corn down the middle and a strip of beans on both sides, leaving a gap in the corn every so often to establish a squash plant. For pollination purposes, we should plant a minimum of two rows of corn in adjoining beds.
If we want to grow a larger-vining winter squash in this system, we will use at least two side-by-side beds, mulching the walkway in between. Then we can plant four rows of corn, starting at the inside edges of the adjoining beds, with possibly some beans on the outside edges, and squash plants spaced among the corn.
I have found that vining crops typically send the biggest mass of their growth toward the east, so it is useful to plant them off-centered toward the western edge of their growing area if beds are orientated north and south.
Commonly we can plant taller plants in the center of our growing beds and lower-growing species along the edges. Where this does not create good combinations, an alternative is to plant short blocks of different crops for maximum interchange of roots.
Most plants do grow well together, but there are a few known antagonists that you should avoid planting adjacent to each other. Many other species do not like to grow next to onions and garlic, but tomatoes, beets, and lettuce don’t seem to mind.
There are whole books written about companion planting if you want to learn from what others have figured out. A complete listing is far beyond the scope of this article. As a general rule, for soil health purposes, we want to grow next to each other a grass, a legume, a broadleaf plant, and often a brassica. The “three sisters” plus a few radish plants would be a complete example. There are many other possibilities.
When combining multiple species into one growing bed, the spacing of the individual species should be reduced, but not to the point of being equal portions. For example, when combining three species such as corn, beans, and squash, we don’t plant ⅓ of a full population of each crop. Instead we would plant a ⅔ rate of corn, a ½ rate of beans, and ⅔ of the recommended squash spacing. This is true of most companion planting. With differences in plant characteristics, the total plant biomass can be increased by 120-180% over single species recommendations.
