When I first learned about companion planting I thought it was a bit of simple folk wisdom. Plant your peas and carrots together, but keep them away from dill. Plant marigolds near the tomatoes, and soybeans with anything. This information, which is available in lists in books and on the Internet, has been my guide every spring when I rotate the vegetables around in my garden. Of course, in my small rotating vegetable garden I am also practicing the most basic element of companion planting which is polycropping, not having so many of one type of plant close together, making it easy for pests to find them, or for disease to spread.

However, over the years I have come to understand that companion plants help each other in a number of ways, starting with providing nitrogen or other chemicals to the soil that one way or another benefit another plant. For example, the carrot growing underground exudes nutrients into the soil, as do other roots, but the carrot’s exudations particularly benefit the growth of peas. This was something I generally understood to be the basis of companion planting.

I knew the ancient three sisters planting of corn, beans and squash was another example of companion planting, but I didn’t take in that the three sister system expresses three kinds of companionate activity. We all know that the beans help supply nitrogen to the corn and squash. In addition, the corn is providing support for the beans in a companionable way, and the squash is keeping down weed growth while helping conserve water.

Clearly there are a variety of ways that plants help each other. Some companions help by making it difficult for pests to locate the target, like your cabbage. Pests locate their target by chemical/fragrance cues, or visually. Polycropping makes it difficult to locate a target visually. Planting flowers like marigolds and nasturtiums, and herbs or aromatic plants like those in the onion family repel pests by filling the air with odors unpleasant to the pest. This aspect of companion planting makes a good case for keeping a number of herbs like borage, basil, and hyssop in the vegetable garden, in addition to in a pretty herb garden close to the house where they are handy to the kitchen.

Trap or catch cropping is another aspect of companion planting. Flea beetles can be a problem for tomatoes and eggplant, as well as for the cabbage family. As much as flea beetles like these crops they like mustard even more. Once you get the flea beetles munching away on the mustard which is planted a distance away from the targets, the trick is to then destroy the mustard and the beetles together. The books haven’t explained to me exactly how to do this without sending the flea beetles fleeing, but I am continuing my researches.

You can also plant flowers in the vegetable garden that will attract beneficial insects like ladybugs, lacewings and beneficial wasps. Some of the best annuals are bachelor buttons, sweet alyssum, lobelia, scabiosa, and dahlias.

Yet another way of using companion plants is by using accumulator plants like comfrey, coltsfoot, yarrow (achillea), and even dandelions as part of your fertilization scheme. Accumulator plants are those whose roots collect various nutrients in the soil and carry those nutrients into the plant’s foliage. Achillea or yarrow is a common, easy care flower in the perennial garden. It also accumulates notable amounts of nitrogen (N), phosphorous (P), and potassium (K) in its foliage. Yarrow is a little living sack of NPK fertilizer, with the three major nutrients required for plant growth. It is not as strong as 5-10-5 fertilizer, but still. Make sure you put these plants in your compost pile at the end of the season, or dry them, crush the foliage and then mix that material into the soil.

Dandelions also have that NPK accumulation as well as amounts of trace elements like calcium, magnesium, iron, copper and silicon. Comfrey accumulates nitrogen and potassium, magnesium, iron, calcium and boron. Although fertile soil contains minute amounts of trace elements they are all vital to healthy plant development.

While I have been concentrating on those plants that benefit each other, one way or another, the companion planting system also notes that certain plants have enemies. Onions are good companions for beets, strawberries, tomatoes, members of the cabbage family and lettuce, but should be kept away from peas and beans.

According to Louise Riotte, author of the classic Carrots Love Tomatoes, fennel should not be planted near almost anything. On the other hand, if it is planted near cilantro, the fennel will not set seed.

There are many mysteries in the garden. Some of those mysteries are becoming understood as research continues. Experiments are difficult in the field because there are so many variables including what effect the wind is having on the garden on any given day.

I do rotate my crops and I do pay attention to plant companions and enemies, but I also know that one of the surest ways to have healthy strong plants is to have healthy soil rich in organic matter. Feeding the soil with compost and organic fertilizers like greensand, and rock phosphate if it is needed is the most dependable way of insuring a healthy garden.###

Between the Rows   March 22, 2014