Are you interested in GARDENING?  Then you might find one of these articles handy:

Weird Things to Grow and Market on the Homestead by Bonnie Lavigne

Give a Fig - New Facts on the Oldest Cultivated Plant by Barbara Bamberger Scott

The Humble Hackberry by Micah Janzen

Monoculture: Is It Really So Bad? by Bonnie Lavigne

Edible Flowers: A Rose by Any Other Name Just Might be Lunch by Adrianne Masters

Small-scale Homesteading: How Much Do You Really Need? by Rebecca Long

Going Bats: The Benefits of Bat Houses on Your Homestead by Patricia Halderman

Victory Gardens - Winners and Losers by Barbara Bamberger Scott

The Four-season Garden by Michael Nolan

Super Tuber! by Neil Shelton

Vegetable Gardening: Your Next Step to Self-Sufficiency by Doug Smith

Attract Wildlife to Your Property by Doug Smith

Pint-size Plow-horses by Doug Smith



The Three Sisters Legacy:

The Science Behind Companion Planting

by Clare Brandt

There’s nothing quite as frustrating as having some know-it-all tell you why your cucumbers aren’t getting bigger than pickles, or why your tomatoes look like tomatillos.  But when that reason seems like some old wives tale that has no obvious logical basis in science, well, that’s just annoying.

I’m a scientist at heart, and I spent the better part of three years sitting in lectures and labs learning all about horticulture and landscape design.  I know which plants attract the same pests and which will suck the ground dry of water or nutrients.  I know how to identify and treat verticillum wilt, and what to do with a slug/caterpillar/aphid infestation.  

But now, here I was being told by an older neighbor—someone who I’ll be the first to admit has more than five times my experience at growing veggies, even if he is a know-it-all—that I shouldn’t have planted my tomatoes anywhere near the sunflowers standing sentry against the back fence.        

“Why?” I ask, which is a big mistake because forty-five minutes later I’m none the wiser and my head is swimming with age-old adages.  A Google search doesn’t help either, on the contrary: I’m left to believe that sunflowers would make a rather good support for my tomatoes, but not my beans.  Plus, now I have a long list of veggies, herbs, and flowering plants (and a few trees) that I should or shouldn’t plant together.

Are these all just old wives' tales, beliefs passed down through the oral tradition from my gritty, old, farmer neighbor and great Aunt Mabel to me?  Or is there some scientific fact hidden here somewhere?  Many scientists, like me, have questioned these adages over the years and have uncovered some truths and some pure hokum.

There is no question that plants influence one another.  Both Varro (a Roman agriculturist) and Pliny the Elder (a naturalist, also Roman) are credited with noting, around two thousand years ago, that nothing likes to grow around the root zone of a Walnut tree.  Walnuts and some other members of the genus Junglans produce an allelopathic toxin—a chemical that inhibits the growth of other plants—called  juglone.  But through scientific research, we’ve also discovered that only some plants are susceptible, while others are unaffected by the chemical.

Even further back in history, while domesticating corn, beans, and squash, Native Americans discovered that these three crops grow better when planted together.  According to Iroquois legend, corn, beans, and squash are three inseparable sisters.  The Iroquois believe each of these three crops are precious gifts from the Great Spirit and are watched over by one of three sisters' spirits, called the De-o-ha-ko.  Iroquois ceremonies to honor the De-o-ha-ko mark the planting season and the first harvest.

Even without the scientific awareness to understand why these companions thrived, the tribes passed on the knowledge—through stories and annual rituals—that corn, beans, and squash should always be planted together.  And this makes sound environmental sense: The beans and corn have a symbiotic relationship in which the corn provides a support for the beans to grow up.  In return, the beans provide extra support for the corn in strong winds.  The squash adds to this partnership by providing ground cover to both conserve water and repress weeds.  In addition, although corn is a hungry feeder, beans (as all legumes do) take nitrogen from the air rather than the soil during the growing season, and so don’t compete for nutrients. 

Whether the Native Americans tried to grow their beans up sunflowers, which also were domesticated and grown by tribes more than four thousand years ago, we’ll never know, but according to my Google list, that’s not a combination that would achieve great success.

Sunflowers, notably Helianthus annuus species (annual sunflowers) produce an allelopathic phytotoxin that inhibits seedling germination and seedling growth in some plants.  Scientific studies have shown that extract from sunflowers are effective in suppressing the germination and growth of certain weeds, namely littleseed canarygrass (Phalaris minor), lambsquarters (Chenopodium albun), lesser swinecress (Coronopis didymus), toothed dock (Rumex dentatus), and burclover (Medicago polymorpha).  Unfortunately, it doesn’t seem there is anything but anecdotal evidence (and about 10,000 Google hits) to indicate that sunflowers stunt the growth of plants like beans and potatoes. 

So where did this list of companion plants come from, and how reliable is it, anyway?

Linda Chalker-Scott, Ph.D., extension horticulturist and associate professor at Washington State University, writes in her article The Myth of Companion Plantings, that, “the problem with using the phrase 'companion plants' is that it is broadly used to describe plant interactions in the realms of science, pseudoscience, and the occult… claims that companion plants can be determined by 'sensitive crystallization' of their extracts (i.e. to discover which plants 'love' each other), or through study of a plant’s rhythm, its vibration, its music, and its note.”

Robert Beyfuss and Marvin Pritts from the Cornell University Department of Horticulture agree that “companion planting is based upon some very bad science,” in particular the sensitive crystallization method, which was created by Dr. Ehrenfried E. Pfeiffer in the 1930s.

Dr. Pfeiffer used chromatography—a method of separating things into smaller chemical components and displaying them in a visual way—to make chromatograms of different plant combinations.  He concluded that those forming bright or clear chromatograms were beneficial, while combinations that made cloudy or dull chromatograms were antagonistic.  Beyfuss and Pritts note that “the notion that carrots love tomatoes but beans dislike fennel is based upon an analytical laboratory procedure and not on direct observation of the plants in nature.  No legitimate scientist believes that this method can determine compatibility among plant species.”

So, if we can’t rely on the observations of Romans, Old Farmer’s companion plant lists, or our great aunt Mabel, what can we rely on to help our garden and veggie plot thrive?

Scientists agree that there are benefits to planting and maintaining diversity, especially with crops.  There’s a certain amount of security in being diverse:  After all, losing an entire season is far, far worse than losing just one crop.  In addition, interspersing crops within the same area, rather than growing in blocks or rows of the same crop has been shown to confuse—if not deter—pests.  Several species in one area can seemingly disrupt the ability of many herbivorous insects to use visual and olfactory (smell) cues to find their host plants.

Similarly, scientists have begun to study the idea of trap cropping, a method where a plant that is known to be attractive to a certain pest is planted nearby the main crop.  The theory is that the pest enjoys the “trap” plant and leaves the main crop alone.  However, Professors Anthony M. Shelton and Brian A. Nault from the Department of Entomology at Cornell University found that in a commercial application, using collards as a trap crop to control the diamondback moth in a field of cabbage “was unsuccessful because it neither reduced the number of larvae on cabbage nor concentrated the insects on collards.”  They did, however, have some success in a controlled environment tempting the moth away from cabbage and broccoli using garden yellowrocket  (Barbarea vulgaris), a common biennial weed.

It’s also been scientifically proven that some plants produce chemicals that seem to repel herbivorous pests.  Common tansy (Tanacetum vulgare) planted alongside potatoes is said to repel the Colorado potato beetle, although tansy itself is listed as a noxious weed in many states.  This ability to repel could be due to the presence of the chemical thujone, which is also found in arborvitae (Thuja spp.), mugwort (Artemisia vulgaris), oregano (Oregano spp.), common sage (Salvia spp.) and wormwood (Artemisia absinthium).

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