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Companion planting

Oct 25, 2010

 This year I have spent some time planting companion plants alongside my vegetables.
I know there is some scientific research for plants like marigold, mustard and maybe camomile but there seems to be very little research on any of the other recommended plants.

The lists seem to be repeated from web site to web site and book to book with very little passing through peoples brains.

The lists of pests they are reported to be effective against read like the old quack cure all medicine remedies.

Is there anyone that can suggest some good research that has been done on companion planting?

I am always amazed at what academics research because they seem to go for stuff that is not very good for everyday life.  In horticulture research, I think that the funding comes from industry so research will be focused on what they think is important.  Companion planting does not seem to come high on their list unfortunately.  Or is it that research has been done and nothing has been found to be effective?

My main worry is the thoughtless copying of long lists of companion planting that I have seen in many books and websites.    I find it very difficult to rely on old wives tales about gardening techniques because I have found that many of them do not work.  The “plant onions or garlic with carrots to keep away carrot root fly” does not work for me and I have tried it for years. 

Now I have read  that planting potatoes next to raspberries encourages blight.  What is that all about?  I have been reading gardening books and research for years and have not heard about that one.  Rubus idaeus the raspberry and Solanum tuberosum the potato both totally different species from different parts of the world. Not only that, I am growing potatoes right up to my raspberries this year.  I can’t put them anywhere else because it would mess up my rotation. 

What fascinates me is that there are very few non cultivated plants within the lists.  If there is something in companion planting, and I think there is, then surely the fact that a plant is cultivated cannot be the important fact.

The fact may be that native uncultivated plants, weeds for short, probably have a greater affinity for native mychorrhizal fungi  and may give a greater help to crop plants than the list companion plants.  Mychorrhiza will be able to transfer any beneficial chemicals to partner plants much quicker, easier and more effectively than diffusion through the soil. 

It may be true what people say,

But I keep wondering anyway…


I use "Geting the Most from Your Garden" from Rodale Press. They did thier own research in the 60's,70's,80's &90's. Long before the fab gardener come along to make money off books & vid's. I think Robert Rodale is the Father of Organic Gardening in North America. But your on trails can be the best way to know anything. Believe nothing & question everything! For the truth will hold it's own, against all falsehood!
I read that onions repel many insect pests, and we certainly saw that in areas that had onions well-scattered through the beds, we did not have the plague of ants that nearly killed a full-grown broccoli plant with no onions nearby. Chili powder eventually drove them to find a new home, but the plant was never the same. Marigolds also did a decent job of keeping flea beetles on the bok choi down to a minimum - the first crop came out looking like lace doilies, but the next crop planted 2 squares over, and around a fresh marigold planting suffered only a few nibbles. I couldn't say that I see much of an effect of Carrots planted next to the tomatoes, though. They both did fine, but those carrots came out no better than ones planted elsewhere. As far as planting the basil in amongst the tomatoes, the jury is still out. The flavor of our fresh tomatoes is amazing, as always, and it certainly is convenient having the basil right, there, too :)
Hi Tony. Welcome to KGI. The point you make about weeds is a good one. It sort of follows my line of thinking. I think the best type of companion planting is to get the biggest mixture possible, rather than to scour books for someone else,s idea of what combination worked in their garden. The big mixture is natures way and weeds form a part of that big mixture. Obviously you need to try to control the mixture by preventing the weeds from seeding and preventing them swamping the vegetables. Weeds can make a good living mulch, as well as possibly providing the right soil environment for nematodes and fungi. I do try to practice what could be described as inverse companion planting. That is i try [ when i remember] to keep certain plants as far apart as possible to prevent the spread of problems from one to the other. Specifically i keep onions and garlic apart to prevent the spread of rust fom the garlic to the onions. I also try to keep potatoes and tomatoes apart to minise the spread of late blight. The only way i could see raspberries affecting the potatoes is by causing a wind break and providing still condtions, where in wet weather the spores could spread more quickly. In my experience onions have never prevented carrot fly from attacking the carrots. This year is my first real success with carrots and that was achieved by using a 2 feet high fleece barrier around the carrot bed. Glenn
I saw your fleece barrier some where. It seem to be easy to put up & take down. Now if I could get a good stand of carrots, so I can use this Ideal.
Hi all-- The best quick reference I have used for years in order to avoid planting "antagonists" next to each other is John Jeavons' "How to Grow More Vegetables... " (a long title)-- while this is not the main topic the advice in the book is based on their on-farm research and not merely a repeated list. It lists plants that are both helpful, and harmful when planted near each other. Jeavons also makes some mention of weeds. A good reference on weeds is "Weeds and What they Tell" by Ehrenfried Pfeiffer, who wrote on biodynamic gardening. Tiny but enlightening. For instance certain weeds can indicate compaction or soil acidity. From what I can tell in some quick research the late blight organism (Phytophthora infestans) is not the same Phytophthora that infects raspberries, which we know as crown or root rot. However on further reading it seems there is possibility that the late blight can transform or move to other host plants that are unusual. So if you have room to keep them apart-- like in separate planting beds-- probably a good idea.
Hi Tony, I agree that it is nice when there is research to explain why some of these methods work. My local agricultural extension office has some information about the science of companions. The link is: I think this is some useful information and have had success with some of the methods discussed in this article. Its extra sweet when the science backs up the folk lore though, don't you think. -Johanna

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