Companion Planting

 Companion planting can be a fuzzy and confusing topic. Books often seem to parrot other books rather than either data or personal experience. Some purported companions, like tomatoes and carrots, are pretty much unworkable.  (Don't miss Carol Deppe's hilarious attempt to make those two work in her book The Tao of Vegetable Gardening.)

​But successful companion planting is something we see every time we walk in the woods or look at a grassy field.

Native prairies combine grasses with legumes and flowering plants in a community that fertilizes and defends itself. Traditional pastures do too. Farmers in many parts of the world grew crops mingled together, some by tolerating chance associations and some by design. A few groupings have been recognized and become standards.

A classic grouping is the Three Sisters of North and Central America--corn, pole beans, and squash (more on this one in the following post.) Traditional African farmers combined millet or sorghum with cowpeas and yams; again, there is a grain, a legume, and a broadleafed groundcover. In the best groupings, each offers a "service" to the others, such as shade, root exudates, nitrogen fixation, pest control, pollinator attractant, smothering weeds, or other benefits. But to be honest, we don't know many of the ways plants interact. Sometimes all you can do is what gardeners have always done--just try things out.

Plant pairings allow you to grow more in a given space mostly mostly by staying out of one another's way.  Here is a checklist for making your own pairings:

• Look for plants with different shapes both above and below ground. Kale and leeks pair well--leeks are tall and thin while kale spreads out. Pair a tap-rooted plant like chard, carrots, or cilantro with a shallow-rooted companion like peas, endive, spinach, or lettuce. Not sure about the root type? Check HERE
• Plants should put different demands on the soil.  It rarely works to pair two leafy greens or two root crops--they both have the same nutritional needs. 
• Match your candidates for vigor as well. Rampant growers like tomatoes, squash, and pole beans need partners that are either equally vigorous--like pole beans with sunflowers--or can live in their shade. In our hot climate, I don't care if my spinach and lettuce gets over-topped by tomatoes--they need some shade anyway.
• Time is another dimension to work with. Radishes are often planted in a carrot row because they mature and are gone before carrots need the space. Lettuce is a space-filler with many crops for the same reason. Kale or collards with winter squash only works if the kale is planted so far away from the squash that the vines don't reach it until the kale has sized up--when it appreciates shade on its roots.
• Don't let companion planting become overcrowding. Maintain adequate root room by widening spacings. Whether it's a weed, or another crop, competition for water and nutrients will prevent plants from doing their best.
• Plants from the same region that are eaten together, often grow well together, as they have been associated over centuries of selection. Crops from Northern Europe often want very different conditions from New World and African crops.  More on this HERE.
• Some plant families have similar vigor but different shapes, and have often been planted together. The parsley/carrot family; the cabbage/mustard family; the spinach/beet family; the onion family; and salad greens of all types have been used in mixed plantings together for a long time, often along with seed poppies or with cool-weather legumes like favas, garbanzos, and peas. A classic spring ensemble would be a row of peas on a trellis with a row of green onions and a row of lettuce or carrots at their feet.
• Caution: green onions and leeks are versatile, space-saving companions that can be tucked in lots of places. But bulb onions and garlic do not want other plants around as they mature their bulbs.   For a guide to the plant families, go HERE.  ​
  

Finding vegetables to match can be difficult. Herbs and flowers are easier to use as companions for vegetables than other vegetables are. 

​They demand less fertility from the soil (often less water, too) and provide the nectar for beneficial insects. In wild systems, the sheer diversity of plants protects them all from pest and disease outbreaks. In gardens, there are fewer kinds of plants, and those are less able to defend themselves. The compounds that help plants resist pests often make them inedible. By growing succulent leaves fruits or seeds for us, plants leave themselves more open to attack. So it is especially important to add lots of nectar-producing flowers for insects like lacewings, minute pirate bugs, hoverflies, parasitic wasps, and other predators to protect vulnerable vegetables. You can find seeds for often-used and effective herb and flower companions HERE

Here are some of the services non-vegetable companions can offer:

1. Attracting Pollinators and Honeybees: Studies have shown that for some crops, yields were higher when 1/3 of the growing area was used for pollinator-attracting flowers  than when the crop took up the whole area. Native flowers and culinary herbs are usually the best, according to research. 
2. Attracting Predator (Pest-Eating) Insects: Herbs with small flowers in a cluster where small insects can land are best. Choose cilantro, thyme, dill, alyssum, orach, echinacea (The large “flower” is actually a cluster of many small ones.) Let some parsnips stay in the ground a second year and flower--you'll be amazed at the number of beneficial insects.
   
3. Repelling pests: Strong-scented herbs confuse pests that target just one type of plant, like squash bugs. They find their preferred food by smell, and may go elsewhere if it's drowned out by other scents. Planting squash seedlings into an existing patch of cilantro, dill, and arugula is a good strategy. Other plants exude strong chemicals from their roots to repel pest species. Marigolds are famous nematode repellents. Wormwood and Euphorbia can repel gophers. Some watermelons discourage fusarium fungus.
   
4. Allelopathy: This is when plants secrete compounds that actively kill or prevent the germination of other plants. The gardener can use this effect in certain situations. Rye's effectiveness as a cover crop is partly due to its allelopathic compounds that keep weeds from germinating. Fennel, dill, parsnips, carrots, and parsley all have germination inhibitors coating their seeds. Juglone poison, which is in all parts of the black walnut tree, is so strong that it can kill mature plants. Some species like currants, beans, squash, onions, grasses, and elderberries are tolerant of juglone, enabling them to live under walnut trees. If you want to grow currants or onions, putting them in the root zone of a walnut tree is a way to limit competition from weeds and other plants. Wormwood herb is poisonous to many annuals and perennials. Deep-rooted shrubs like roses are not affected. I plant wormwood beneath my roses to repel gophers, weeds, and to some extent, deer.
5. Enhancement: A few plants actively help other plants produce bigger, or higher-quality, crops. One way this happens is by producing sugars and other nutrients which leak out of the roots into the soil. These are called exudates. Beans, peas, vetch, and other legumes have bacteria in their roots that can concentrate nitrogen out of the air. One newly-recognized way plants help one another is by enhancing the production of essential oils. Apparently, plants sense terpenes and other aromatic compounds in the air and produce answering terpenes of their own. Good terpene enhancers are fragrant herbs like basil, savory, thyme, hyssop.