There are volumes written on companion planting, the inexact science of plant relationships. Some relationships are scientific common sense, while others remain a bit of a stretch even by old wive’s standards. This post looks at common sense companion planting and how to combine plants using commonly found characteristics. Not included are those plants that use their scent to attract or repel insects. That is for another post at another time.
There are six characteristics to consider when creating plant communities, three major and three minor. The major characteristics are climatic needs, nitrogen fixation, allelopathy. Our first question after seeing a new plant we want to grow is, will it grow under my garden’s conditions? Compatibility of climate, water and soil needs are the most important considerations we face when designing our plant layout. Every other companion planting decision stems from these three initial considerations. Next nitrogen fixation is the ability of a plant, like peas, beans, clover, and alder to absorb atmospheric nitrogen and put it in the soil in a form that is available for other plants to use for their own growth. By using “N-fixers” you can reduce inputs of nitrogen fertilizers. In contrast, allelopathy is the ability of plants like cabbage, sunflower and walnut to inhibit the growth of other plants by secreting mildly toxic chemicals in to the soil via their roots or leaf litter. The reason for this is simple: the less competition they have, the greater their chance for survival.
Okay. Now for the minor characteristics: height, ground coverage, and root structure. The height of a plant can determine the amount of shade it casts and potentially the vertical growing area for another plant. Plants can also act as living mulch by covering the ground helping it retain moisture. The last major characteristic is root structure. Plant roots occupy different niches in the soil like their vegetative counterpart does above ground. This diversity plays just as crucial a role as it does above ground. Some plants, like squash, have relatively sensitive roots that can’t handle too much disturbance. For this reason root crops carrots that will be harvested regularly cannot be planted with them.
Looking at the common Iriquois planting of corn, beans, and squash (known as the three sisters) we can find five out of six of these characteristics at work. The beans are planted two weeks after the corn at the same time as the squash. The beans use the corn to climb and in return offer nitrogen for the corn to use in its growth. The squash covers the ground as living mulch for the corns and beans and in return the corn provides shade and the beans nitrogen for growth. Their roots all occupy different depths and widths in the soil making existing in the same location that much easier. The synergy of this community increases yields 50% more per acre than plantings of the individual crops on their own.
Companion planting is not a veggie growers science alone. It can be used in ornamental gardens as well, but to really benefit from companion planting we need to know our plants and the characteristics they have and then get creative and experiment, so have fun with it and explore. A bounty of sense stimulation awaits you!
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