Companion Planting: Fraud vs. Facts


Sometimes common knowledge, what everybody knows to be true, just isn’t.  That’s the case, I’ve found, with much of the broadly accepted information about companion planting.

Do tomatoes really like basil? (By Gausanchennai – Own work, CC BY-SA 4.0,

Tomatoes, for instance, are supposed to “like” basil; similarly, chives and carrots supposedly “like” each other.

Where does such information come from?  That’s what I began to wonder a number of years ago.  Why should tomatoes like basil?  Typically, the sharer of this information couldn’t say.  I went to organic gardening literature, which usually just presented the companion planting combinations as fact.  By comparing many different accounts of companion planting, however, I eventually identified a source.  A number of the books credited Ehrenfried Pfeiffer as an originator of companion planting know-how.

And if so, is the feeling reciprocated?  (By Castielli – Own work, CC BY-SA 3.0,

A trip to the New York Botanical Garden Library revealed who this mysterious authority was.  Ehrenfried Pfeiffer was a German immigrant who was a disciple of Rudolf Steiner, a late 19th century, early 20th century Austrian philosopher and mystic.  Among other activities, Steiner founded biodynamic gardening.  Pfeiffer was one of only a handful of people that Steiner entrusted with making his biodynamic “preparations,” such as preparation #502 which called for yarrow blossoms to be stuffed inside the urinary bladder of a red deer and exposed to the sun over the summer, then buried over the winter before being exhumed and used to inoculate the compost heap.

At Steiner’s behest Pfeiffer also developed a procedure he called “sensitive crystallization.”  In this process Pfeiffer would mix some biological extract with a solution of copper chloride and pour the result into a petri dish to observe the pattern of crystals that formed as the liquid evaporated.  He applied this process largely to the study of plants.  If the plant extract contributed to a clear and orderly pattern of crystals, Pfeiffer judged this to be a sign the plant was healthy.  If the pattern was unclear or disorganized, Pfeiffer took this as proof that the plant was unhealthy.  When two plant extracts were combined with the copper chloride solution, an attractive pattern was proof that the plants were compatible and should be grown together.

Pfeiffer published his observations as a companion planting list.  Picked up and endorsed by J. I. Rodale, an early leader of the American organic gardening movement, this list of supposedly compatible plants became a popular tool of organic gardeners, who usually did not know of the nature of its origin.  Passed down from book to book, Pfeiffer’s dubious findings are still promulgated as gospel today.

Does this mean that all companion planting information is bogus?  Not at all.  There are people who have pursued a more science-based take on this subject.  I’ve interviewed one of them, Robert Kourik, on a podcast at

Previous articleFall Foliage in a Townhouse Garden
Next articleHard Pruning with Attitude Amid Lingering Dwarf Conifer Issues
Thomas Christopher

My father was a compulsive tree planter, but it was my mother who taught me the finer points of gardening.

Her homeschooling was followed by two years in the New York Botanical Garden’s School of Professional Horticulture, and then ten years as horticulturist at an Olmsted Brothers designed estate on the Hudson River Palisades.

I’ve worked as a horticultural journalist for 35 years, contributing to publications ranging from Martha Stewart Living to the Journal of the Royal Horticultural Society and The New York Times.  My most recent book is Nature Into Art: The Gardens of Wave Hill, which is a tour of the lessons to be learned from that great public garden.  I’m currently focusing on my new podcast (at which features weekly interviews with leaders of environmentally-informed gardening.

My special enthusiasms include sustainable gardening, especially sustainable lawns;  heirloom chicken breeds; and recreating vintage New England hard ciders.


Contact Tom by email


  1. Okay so probably most people have heard this, but maybe younger folks have not:

    Isn’t this like the young housewife who, when cooking a pot roast, dutifully cut off both ends before putting it in the pot? When a friend asked her why, she answered, “Well, my mom always did it that way.” Later the young housewife asked her mother, “Mom, why do you always cut off the ends of a pot roast?” Her mother replied, “My mother always did it that way. Not sure why, but her pot roasts were delicious.” Finally, when grandma came to visit, both mother and daughter asked grandma why she cut off the ends of her pot roast. Grandma’s answer: “Because my pot was small, and it wouldn’t fit.” Tradition & common knowledge are fickle.

  2. There may be two different sorts of ‘companion’ planting. Whereas tomatoes and basil are grown together because they go so well together on a plate, companion planting is more often a diversionary tactic against predators.
    Grow French marigolds among tomatoes. Marigolds emit a strong odour that will repel greenfly and blackfly.
    Grow sage with carrots or plants in the cabbage family to ward off pests. Both have strong scents that drive away each other’s pests.
    Plant nasturtium with cabbages – they’re a magnet for caterpillars that will then leave the cabbages alone.
    Garlic planted among roses will ward off aphids.
    Plant carrots and leeks (or chives) together on the allotment or vegetable patch to protect against a number of pests. Leeks repel carrot fly and carrots repel onion fly and leek moth.
    I have followed several of these tactics and bear testimony to their efficacy. Hopefully US bugs will read and be scared!

    • There are plant associations that are mutually beneficial, or at least that benefit one of the partners. Notable among these are plants attract predacious insects that prey on insect pests that afflict neighbors. However, surprisingly few of these associations have actually been scientifically researched; most are just based on anecdotal evidence.

  3. Thank you Gaynor Cooper. I planted marigolds with tomatoes and they had no pests this last summer. Other years planted tomatoes with basil and had to pick caterpillars off the tomatoes. Thank you for your other tips and especially your English humour !!

  4. I transplanted some nasturtium under my lemon, which was falling prey to every bug in the neighbourhood. Admittedly, that wasn’t all I did, but the lemon has perked right up. The nasturtium is looking a little chewed, mind you, but there’s plenty more where that came from (I harvested 3 cups of nasturtium seeds for pickling just the other day).

    Exhuming a well-aged yarrow-stuffed deer bladder, on the other hand, I think I can do without.

  5. Some bald-face hornets set up a nest near my vegetable garden a few years back. That summer, I had nary a caterpillar in my garden. Coincidence? I think not! LOL

  6. I believe the “sensitive crystallization.” procedure is a great idea.
    I want to grow tomatoes in my own garden. This article helps me a lot.

    Keep up the good posting, Thomas.

Comments are closed.