Science behind companion planting

Does anyone know of any rigorous scientific studies carried out on the purported individual and group companion planting relationships? The experiences I've found online indicate they're hit-and-miss - some being spot on and others either having little effect or even a noticeable effect to the opposite supposed!

There's certainly science behind some incompatibilities - potatoes and tomatoes, for example, since they're of the same family and share disease - and certainly for some compatibilities, such as interplanting heavy feeders with nitrogen fixers, but I'm really interested in seeing if anyone's run a scientific control study of plants grown in the same environment both in and out of the purported positive/negative relationships.

As well as this being the first year setting up our permaculture homestead, we're also working on a project for plant information including inter-relationships, and I'd love to see something which could help us discern the science from the folk-law.

Thanks!
Andru

(PS. First post here after a while lurking unregistered - hello!)

Do a google search, with criteria = companion planting edu. There's a few nice articles, such as http://www.aces.edu/counties/Limestone/MastGard/companions.htm:

Plants with strong odors do confuse, deter, and oftentimes stop certain pests.
-Certain plants hide other certain plants we don't want detected.
-Certain plants, and especially herbs, are considered nursery plants for the good insects providing shelter, nectar, pollen, and even dark, cool moist spots for lacewings, lady beetles, parasitic flies, and wasps.
-Certain plants serve as a 'trap' crop, which pushes insects away from other essential plants (rue's bad odor and disagreeable taste will keep even the most persistent of pests away).
-Certain plants create habitats which attract more beneficial insects (such as lady beetles, praying mantis, and ambush bugs).

There's also a rather critical one, http://www.puyallup.wsu.edu/~linda%20chalker-scott/horticultural%20myths_files/Myths/Companion%20plants.pdf.

Years ago I picked up a used copy of Rodale's The Encyclopedia of Organic Gardening, and it in part describes companion planting similarly to a guild- certain plants will benefit from the shade of other plants; some plants bloom early before their neighbors have a chance to leaf out and shade them.

I have a feeling that the reaspon there's not much scientific data on this is because of funding sources. Who is going to fund a study that will prove a way to minimize chemical intervention? Not the chemical companies.

Start small, with the simple concepts, or you'll get overwhelmed. Then branch out as you feel comfortable.

Good luck (and welcome!).

Thanks for the reply Sandra, the PDF is interesting and I largely agree with the conclusions it draws: there are plenty of examples where companion planting rules have hit the nail on the head, but many sources lack credibility or scientific rigor. I'm doing some googling with 'edu' on the end now, thanks for the tip!

The article you posted from aces.edu was very useful! It's great that it explains which pests are repelled by what, but there are still some items which are unexplained. That is my main complaint with most companion planting data I've found: there's a way but not a why. Plenty of tables and databases telling you what to plant with what, but only rarely why. For example, from that address (and I've seen this particular example on many more, since we're planting loads and loads of beans!

Beans
Plant with
Beets, Cucumbers, Corn, Radishes, Rosemary
Do NOT plant with
Onions, Garlic

I can understand intuitively why beans will work with corn, because they do not compete for light and in the case of vine beans the corn can provide a structure for the beans to climb. I can guess at why radishes and beets would work, probably because they provide a good ground cover and aren't heavy feeders. However, that is only a guess, I'd love to see a companion planting website which actually explains these relationships in useful terms. Why do onions interact badly with beans? Do they exude a chemical from their roots? Do they dislike the partial shade of beans overhead? Is it a modern observation or old folk-law? Without explanation, it's a system which simply demands adherence to rules without understanding, and that's not something I can live with

That website provides some interesting reasoning behind the pest confusers element of companion planting. I'd love to see any further literature anyone knows of with extended reasoning behind each interaction.

If you wish to delve a little deeper, here is a site that offers 2 dozen links concerning companion planting.
Some are repetitive, but they also include some university links.

http://www.ecoccs.com/resources_links.html#companion

Andru Vallance wrote:Why do onions interact badly with beans? Do they exude a chemical from their roots? Do they dislike the partial shade of beans overhead? Is it a modern observation or old folk-law? Without explanation, it's a system which simply demands adherence to rules without understanding, and that's not something I can live with

In my own garden, I have noticed that bush beans perform markedly better (less insect damage) with bunching ("Welsh") onions nearby, but the onions appear twisted and deformed. The databases I'm consulting just cite "traditional literature" for the incompatibility between beans and onions. My own research is anecdotal and not very methodical. More research is definitely needed!

Photos from earlier this month demonstrating this relationship:
bush bean without onion nearby: http://interdependentweb.com/sites/interdependentweb.com/files/2012-05-09%20bean%20without%20onion.jpg
beans of the same variety with a bunching onion in their midst: http://interdependentweb.com/sites/interdependentweb.com/files/2012-05-09%20beans%20with%20onion.jpg Note the deformed, twisted appearance of the onion. This variety usually grows very straight.

I'm studying horticulture in college and this is one of the things that routinely amazes me. It's not difficult to come up with ideas for experiments and trials, and yet so many of them go undone. A lot of what we don't know is fairly low hanging fruit as far as scientific discoveries go. Sandra is right from what I've experienced, there's just no funding. Most of the big trials that are done in agriculture are done to figure out how monocropped "conventional" farms can squeeze out another penny per acre of profit by using a new chemical. This is part of what drives me in my studies. There is a definite lack of interest in the agri-science community in small farms and permacultural things like guilds.

Sometimes research is actually actively discouraged. There's an entomologist here in California who has been researching organisms that will act as predators or parasites of the asian citrus psyllid which is a vector for Huonglongbing disease a horrible affliction for the citrus industry. He went through the proper channels and was about to sell this bug to growers within the quarantine. The state actually stopped him because the psyllid is part of an eradication program in this state and they won't hear of long term mitigation measures since they just want to spray shit to death with expensive chemicals. I've encountered university studies showing that partially composted woody mulches fight off Phytophthora sp.(a very infectious genus, P. cinnamomi is the cause of the most significant avocado disease in California) because the same fungal enzyme that breaks down cellulose in wood degrades the cellulosic compounds of the Phytophthora's cell walls. Hosting innocuous fungi also helps to fill the niche that would otherwise be waiting for the pathogen. Other studies have shown that certain areas in San Diego have something in the soil that is antagonistic to Phytophthora but these concepts just sit there in dormancy until some college student like myself comes by willing to pour in our time for a grade. I'm sorry to have gotten so off topic but this notion of selective funding is frustrating and dear to my heart.

A couple of things that are promising are that many of my fellow students either already know of permaculture or are interested to learn more when they first hear about it. Going into school I was afraid it was going to be all miracle-gro and roundup but some of the teachers are pretty hip. The other thing is that there are a lot of scholarships available for horticulture students. There's really a need for young people to get into this field. I'm still in community college but so far I'm attending school for free because my major and my grades.

Long story short: I'm surprised we haven't tested more of this stuff but in a certain way happy because it's all opportunity for me in my education career.

I, too, have found very little information on companion planting to guide my design decisions for the food forest we are planting. I am in the middle of reading Edible Forest Gardens, by D Jacke, in which he states that little research has been done on this. That was published in 2005 but it appears to still be the case today. Basically, I think we are all doing experiments now, and if something works, we should share that info. For my guilds, I am planting things together that have similar pH and moisture requirements, while not being competitive because they have roots and canopies at different levels, and they have different nutrient requirements. And we are trying plants that serve each of the required ecological functions - insectary, nutrient accumulators, grass suppressing bulbs, nitrogen fixers, wildlife cover, wildlife food, nurse plants, trellis plants, etc. In the coming years, we'll figure out what works and what doesn't for our location. It's not a rigorous scientific experiment, but it's still should end up being useful for others in our locale.

I think this is happening now for many locales all over the world. While it's disappointing that we don't have better information to guide our decisions, it is exciting that we are on the cutting edge of acquiring that knowledge.

This is a great site that tells you the reasoning behind most of its recommendations. http://www.ghorganics.com/page2.html
These include trap crops, dynamic accumulators, nitrogen fixers, mulchers, etc. I hope that helps.

Tony Gurnoe wrote:I've encountered university studies showing that partially composted woody mulches fight off Phytophthora sp.(a very infectious genus, P. cinnamomi is the cause of the most significant avocado disease in California) because the same fungal enzyme that breaks down cellulose in wood degrades the cellulosic compounds of the Phytophthora's cell walls. Hosting innocuous fungi also helps to fill the niche that would otherwise be waiting for the pathogen. Other studies have shown that certain areas in San Diego have something in the soil that is antagonistic to Phytophthora but these concepts just sit there in dormancy until some college student like myself comes by willing to pour in our time for a grade. I'm sorry to have gotten so off topic but this notion of selective funding is frustrating and dear to my heart.

Hey Tony, any chance you'd be able to share some of your references regarding Phytophthoria? People are becoming increasingly worried about it here in the UK so it'd be nice to do a little research on combating it.

Burra has a post in Meaningless Drivel called "How Biodiversity ...." That has an article from Scientific American pointing in this direction. What would a scientific approach set out to prove specifically? Possibly about plant height , root systems , water use and water/condensation gathering , varying nutrient usage and nutrient production , etc. Seems like it would entail alot of different studies to create a large picture. I could show them that the only apple tree that is thriving this year here is the one that is surrounded by lettuce plants , even the mulched trees are suffering this year. Anectodal evidence has some value.

Here's the link - How Biodiversity Keeps Earth Alive

I too agree with you.

We just cannot rely in a simple table without knowing the why. Probably most tables are just untested and false information.

I have been testing some combinations, but they are obviously difficult trials to set.

So far, most vegetables seem to be happy growing with other vegetables, except that their soil requirements are sometimes very different and therefore difficult to combine. For instance, carrots like to grow in a sandy soil, while potatoes enjoy a rich fertile soil. Tomatoes like rich soil with hot and humid conditions, while lettuce would readily bolty under such conditions. And plants might compete for nutrients if too close to each other but benefit if somewhat spaced. So, there is no absolute.

Obviously growing potatoes leaves less light for small crops like beets and carrots if planted at same time, but jerusalem artichokes so far grow at same speed as potatoes and both do not exclude each other for light. Carrots can be grown best with onions because of their tall habit, which does not exclude their light as a brassica would do. A squash needs plenty sunlight, so obviously it need clear space around it.

I tested beans and onions and they seem to tolerate each other.

What I discovered is that most vegetables (like brassicas) grow better if mixed together, or at least with flowers and herbs, because this seems to repel or confuse pests. It certainly works with most crops.

So far I haven't yet seen a negative relationship of a combination of two specific two vegetables.

I think it is most related to soil and light requirements rather than true allellopathy.

Has anyone seen anything like this: 2 months ago I planted 5 true rozelle plants (aka cranberry hibiscus). They were only 3 inch long sprouts. Two of them were planted right next to other plants, while the other 3 had lots of empty space around them. All 5 were planted in soil of equal quality - pretty sandy with a little composted cow manure mixed in. They were all mulched with a couple of inches of shredded oak leaves/pine straw mix. All 5 are in full sun all day, and have received about the same amount of water.

I thought that perhaps the two that were planted close to other plants might not do as well because of the competition they would have to endure. However, the complete opposite has happened. Those two plants are now 24 inches high and wide and 3 to 4 times more massive than the other 3. The two "companion plants" are similar - one is apple mint and the other is greek oregano.

Is this an effective companion plant combo? Or is it just a coincidence? It would be interesting to see if anyone could duplicate this "experiment" and help answer that question. Or maybe someone's already seen something like this?

Assumption that an observation contains no truth is as unscientific as assuming that some observation is true without evidence. Absence of evidence is only that, absence of evidence.

Scientific investigation is 'expensive' (of time if not money) and so it comes as no surprise that scientific effort follows profit.

Soil, variety, the year in question, exposure, latitude, climate, and year to year variation could all affect something as subtle as synergy.

I think the most powerful evidence (that I can't cite off the top of my head), is that polyculture can result in increased yield compared to monoculture, simply due to niche separation in time and space. (I'd l.ook to agroforestry literature in silvopastoral systems, or obtaining vegetable yield in a young orchard.) I can see no reasonable argument why this wouldn't also apply to smaller scales... (although you'd have to account for the labor of the gardener if you are really digging for 'evidence' to challenge the agricultural institutions).

All this said... science progresses poorly without a strong basis in observation. Only when people experiment and speculate and observe and develop postulates that are based on extensive experiment, only then can science attempt to isolate effects and mechanisms of species interactions in vegetation.

And in all this we have not settled on the potential power of intuition for solving problems in complex systems... the evidence be damned... can you argue that a experienced and thoughful gardener can make a garden grow better than a lab technician?! How do they do it. They do it in a million different ways, far beyond the reach of science.

Hi Nick,

I can understand why that might happen with your hibiscus. But it is just a theory

Maybe nearby the fine roots of oregano and mint conserve more humidity than the bare soil around the other hibiscus. Therefore the hibiscus planted there might grow faster.

There are many factors; so it is difficult to understand the "why", but one can test any combination and see how well plants grow.

Melissa Bush wrote:This is a great site that tells you the reasoning behind most of its recommendations. http://www.ghorganics.com/page2.html
These include trap crops, dynamic accumulators, nitrogen fixers, mulchers, etc. I hope that helps.

So I was going to use this site as a guide for companion planting... are you all saying that it may be pointless to do so? This site does explain the reasoning behind certain groupings, which made logical sense to me, though I haven't tried any of them yet. It seems to me that if many gardeners are companion planting and observing similar results, then those results could be put into a table such as this one. Why should we assume that all tables are false information?

Why to know why I say that these companion planting tables are not to be trusted? They said "do not grow mint near parsley, they are enemies" But then I found people who grow both together with no problems. Take them with a grain of salt. Some of their claims and advices are however correct.

I also have grown beans with onions and both grew well. So, why keep these tables say they don't like each other? Some of their information is correct, but a lot else is foolish stuff.

What I have seen from my experience:

Yes, basil seems to grow well near tomatoes, with tomatoes unaffected. However tomatoes seem to be unsocial to many other plants; I planted beans near tomatoes, both seemed to stunt each other.

Another curious find (and opposite to most tables) was that by growing mustard near a brussels sprout, the cabbage was growing better, compared to a control without mustard around. Usually to repel brassica worms, I need to grow several flowers and aromatic herbs around the brassicas, not only a single one, but a mix seems to deter them. Onions however don't seem to be enough to repel the cabbage worm.

I planted beans near many other species and they grown well (for example turnips), and they also grew near chines and onions (against companion planting table advice), but I noticed they failed twice when I tried them in a parsley patch.
I planted parsnips near carrots and there was no problem (again against the tables). Onions also grew very well with carrots (and might have helped repelled the carrot fly). I have had good experience of growing celery near lettuce, onions and beets.

I have a few fennel plants scattered over my garden; I never notice any negative effect (alellopathy) from them. I have parsley, catnip, celery, squash and broccoli growing near them. However, and accordingly to companion planting advice, beets and beans seem to stunt each other (but not a eggplant growing between them).

I guess these interactions are more complex than simple tables. I would love to hear about you guys experiences!

The thing that comes to my mind is that you can evaluate what has happened with companion plants
but not why it happened with any degree of accuracy. They may have done well or poorly for reasons other
than those that you are trying to evaluate. So scientists are really out of luck putting a finger what made what
happen. They can theorize just like gradpa.

When I think about plants growng together, questions about compatible height, spread, root systems, sun, water and nutrient requirements are plenty complex for me!
I've never done, and more than likely never will do controlled field tests, but I kind of imagine allelopathy et al would only have any kind of measurable effect if every other variable in my garden was removed.

So I know this thread is super old but I found this nifty little info graphic and wanted to post it somewhere. I think it would fit well here because it is a table which a bunch of you are not trusting on this thread. However, it has a bunch of legit sources at the bottom of the image. It has real info backing it. I like that.



Thanks for the image,
Anglian Good To Be Home

Thank you for sharing that helpful graphic, Cassie! I really like cucumbers, and its nice to know that if I plant radishes around them I will probably get to eat a few of them myself!

You are very welcome! I think next year I might do little square raised beds with these combinations in them.

Nick Garbarino wrote:Has anyone seen anything like this: 2 months ago I planted 5 true rozelle plants (aka cranberry hibiscus). They were only 3 inch long sprouts. Two of them were planted right next to other plants, while the other 3 had lots of empty space around them. All 5 were planted in soil of equal quality - pretty sandy with a little composted cow manure mixed in. They were all mulched with a couple of inches of shredded oak leaves/pine straw mix. All 5 are in full sun all day, and have received about the same amount of water.

I thought that perhaps the two that were planted close to other plants might not do as well because of the competition they would have to endure. However, the complete opposite has happened. Those two plants are now 24 inches high and wide and 3 to 4 times more massive than the other 3. The two "companion plants" are similar - one is apple mint and the other is greek oregano.

Is this an effective companion plant combo? Or is it just a coincidence? It would be interesting to see if anyone could duplicate this "experiment" and help answer that question. Or maybe someone's already seen something like this?

I think the idea of 'companion plants' or whatever is too complex to really nail down all the relationships without having SO MUCH TIME AND ENERGY TO BURN. Plants live with other plants. This is their most natural environment. I do believe that being planted near the mint/ oregano is the primary cause of the accelerated growth, but I think that would have happened had you planted it close to most anything. In my limited experience plants that don't kill other plants make them stronger. The stuff that makes it through my mat of giant pumpkin leaves is HEARTY. The stuff that is low growing likes some shade. The stuff that is tall seems to like having the spaces below filled out making it difficult for browsers to go on the attack. Plants usually like other plants, IMO.

Your little experiment is absolutely valid, but needs to be replicated about 100 times or more to become scientifically valid. And then it only addresses the relationship between rozelle and mint and oregano vs. rozelle alone in one climate during one season. This is a problem with scientific studies of this type. You can't come to broad sweeping generalizations with one or two studies over the course of one educational term. You need many controlled experiments over extended periods of time requiring land and other resources and you need to target specific conclusions otherwise your experiments will hold too many variables to be useful to the scientific community. So anecdotes continue hold sway.

Hi all!!

This is my first post at Permies forum!!

I also tried to find out the science behind companion planting an year back. I think the book "Carrots love tomatoes" is considered to be a classic in this. This article Companion Planting Logic resonates with my reasoning! In my garden I always do companion planting, but to say that there is a definite benefit I would have to do trials a bit more scientifically. And also sometimes despite the best efforts, pests do make way.

Sai!

I just saw this thread. Robert Kourik, in his book Designing and Maintaining your Edible Landscape—Naturally has a section on companion planting and his skepticism about it, with a chart showing experiments that support or disprove various traditional companions. The book is 20 or 30 years old, so maybe more work has been done since then, but what's there is likely valid.

thanks you all for these ideas.

my first response to the topic is that i do not believe that most companion plants (or guilds) work everywhere. it seems to me that soils, climate, etc will influence what plants like each other or do well together. we do see alders with stinging nettles in a lot of place. i even saw them in nepal. so maybe there are companions that work in a lot of areas and companions that work only in some areas.

my next issue is the science behind anything really. i am a chiropractor, a graduate of fairly rigorous scientific program, and a lifetime student of the human ecological system as well as lifetime student of land based ecological systems. I have to say that i am appalled at what science does not investigate and how crippled science is because of this. as we all know and it was mentioned here that science reflects what it is paid to study.

when i was a chiropractor i had a patient who had a slow growing type of cancer. she had been going to medical and alternative folks for 20 years and still the cancer persisted, sapping her vitality. when she came to me, i intuited that she needed black strap molasses. She said why, I said i do not know, but taking 2 tblsp per day in a glass of water certainly will not hurt you. she followed through and 3 months later the cancer was totally gone and her vitality back. I suggested that she continue with the black strap molasses, 1/2 tsp in glass of water for the rest of her life, as possibly she had a condition where her body was not making something that this had. 3 years later i read in some fancy medical journal that her particular kind of cancer was helped by a certain item which was found in black strap molasses. sorry that was 30 years ago and i do not remember any of the particulars. (no i do not regularly read fancy medical journals, we will not discuss the serendipty of me finding that particular medical report).

i was recently reading claude bourguignon''s book Regenerating the Soil, where he states that all agriculture research is looking at the chemical side of farming (our "friends" NPK). he is an agronomist and microbiologist and states that most of the plants needs are met from its leaves, with a very small amount coming from its roots (I believe his number was 5%) and this is fed by the soil microbes. I would add dynamic accumulators, but then their minerals are transferred by the mycorhizzals. Hooray Elaine Ingram.
Now i did not wait until i read this book or Elaine Ingram's work before i started working with soil microbes. i started 45 years ago feeding the soil and not the plants. i did not say what is the science to what i am doing. On good days I live in my farm, learning from all the beings there. What i learn from them is what i do I am blessed to be from a multigenerational peasant background (even my father was a hobby farmer). when you live in your farm you become connected to the seasons, to the earth, to the plants, and they teach you what you need to know. it comes (for me) in the form of waking up in the middle of the night with an understanding.

science is extremely reactive and our job is to lead not follow it. if on bad days we are feeling like we are crazy because of some idea we have learned from living in our farms, then we need to read other permaculturists. although when i was innoculating my victory gardens (650 of them) just 10 years ago, most permaculture people thought i was wrong.

as i say when i do permaculture presentations, i learn from my farm and often i am not very articulate or current with how to explain it all. so i read to prepare for my presentations,, especially when books like Regenerating the Soil fall in my lap, so i can talk to where people's minds are. i think our minds are also reactive. our minds are after all trained to focus from what dregs of science have been incorporated into our school systems, magazine articles, books etc.

and more now that i am on the topic

While working as a chiropractor, I was known for relieving unrelenting pain. I was referred patients by medical doctors and many other health care practitioners. I ended up with about 100 patients with end state cancer. This means they were sent home to die.

After I helped the cancer patients get rid of their pain, I suggested that maybe they wanted to go on our program. We would work to get the body (the ecosystem) healthy.

The details are not relevant here, but the basis of the work was that I found out where the system was open, where I could use the least amount of effort, and applied a small amount pressure to allow it to open up more. This is systems theory (which I had never heard of at the time). Great book for lay people, if you want to know more is Peter Singe, The Fifth Dimension. I learned these principles from my study of homeopathy.

Our job in permaculture is to apply these principles to our land. Example: In my demonstration farm the land told me it wanted water. Yesterday I made 3 swales. We know from past experience that this will produce a lot of weeds and many more things which I will observe. Where the weeds are will be relevant. My agenda is to plant a lot of dry land fruit trees and have them produce gloriously. My goal is to bring back the ground water as well as to have a monetarily productive demonstration for the local farmers who are hurting without water (as well as great soil, 100 bottom lines). Maybe the land has another agenda which might be even more effective to bring back the ground water and serve the farmers, than the one I came up with. It is my job to observe, and learn. I am a partner to this wonderful process with nature and i am most definitely the junior partner.

Hi everyone,

I'm new here and was looking at that infographic posted above on their website and they've made an interactive version which is really pretty cool. Let's you make your own version depending on where you live - https://www.anglianhome.co.uk/goodtobehome/personalised-vegetable-cheatsheet/

Hope it helps!

I will have to get it out of storage but I have a small book that was published by people out of UC Berkeley in the 1970s where they did a fairly scientific study of companion planting. That said, its funny how often you see different sets of companion planting listings and I think that is because people are so desperate for online content misinformation spreads so fast! I will dig up the book and see if I can find it online, if not, I may have to scan it and post it somewhere.

Also, there is a vast difference between what plants do in different regions. Here in Sacramento where it is HOT, Cilantro just sprouts and sits there doing nothing when its hot. Mint will take over anywhere the soil is moist. In Berkeley, I did a shade garden for a girlfriend in an area that already had mint, the cilantro CROWDED the mint out, it blew my mind!

The funding problem may also be related to how science goals are achieved.

There are several scientific methods that are applied widely.


1) Observation, describing, timing and counting.
2) Geografical method : Basically put your observations on a map and look what else follows the same pattern. Say you see that a plant in his natural habitat occurs in peaty soil.
3) Isolation of parameters : You keep as much of the variables in your system (here perhaps a pot with soil) constant and variate one parameter (different variaties of beans ?).
4) Modelling.
5) Critique.
....

I think the problem sits with nr. 3. In permaculture we grow lots of stuff together. How do you isolate the affect of one parameter in a whole bunch?


Say you have a plot 1m² plot. You want to know what happens to beans when you plant 10 companion species ? 1 plant may be beneficial - 5 neutral - 3 beneficial/harmfull depending on circumstances - 1 may be harmfull.
Then you have to measure everything......
Say you find a clear effect. Then you must reproduce that effect at onother field. Al that while you generally don't know what is in your soil, what fungi are there, what diseases are there, .....

The problem becomes unmanageable very fast. Quick results ..... impossible? Statistics, modelling and supercomputing highly desirable. No wonder that the soil 'problem' is tackled first from the chemical, granulometric, hydrological and mineralogical perspectives first.

The only way around is local experimenting on a vast scale with lot of (amateur?) scientists/observers. I guess that may be us
Problem here is that nobody is reporting in a rigorous, scientific way that can withstand scientific scrutiny and critique. And that can be reproduced on a reliable way elsewhere.

When i studied soils at the university - fungi where not even on the curriculum. That changed only when the possible role of fungi in soil remediation became apparent. So perhaps it is not as much that there is an active conspiracy against this or that. But it may be that the people who allocate scientific grants are not convinced that is an attainable goal.
I think that we should aime for a citizen science project that helps us report our observations and quides to correct observation.

charlotte anthony wrote:thanks you all for these ideas.

my first response to the topic is that i do not believe that most  companion plants (or guilds)  work everywhere.  it seems to me that soils, climate, etc will influence what plants like each other or do well together.  

This makes perfect sense because marginal soils might not be able to support 2 plants that needed the same nutrient, but soils with an abundance of that nutrient may be able to support them both.

I think I have a new article in limbo (not yet submitted), but some feedback would be nice to help when I get a chance to restart.

There are lists of companion plants which pair A and B.  Some lists will list a companion if B helps A (B is a good companion for A).  Some will list a companion if B helps A or A helps B.  And many of these lists are inconsistent within themselves; let alone compared to other lists.

My feeling is that companion is more complex.  It at most is just considering nearest neighbour.  I've seen notes that two different species need to be planted at the same time; but no notes like (must be planted 3 days after the other plant).  It could be that the companion lists are climate sensitive.

I am beginning to think the allelopathy is more prevalent than I had been expecting.  A couple of years ago, I tried some 1x1 foot plots in my fescue pasture to grow calendula and/or faba bean.  Some plots germinated, no plants were successful.  This year, I have tried 2x2 plots to grow squash.  The longest vine on any of my squash "plants" is maybe 3 inches long.  Yes, we've had a lot of rain and not enough heat this year.  But this could also be fescue  retarding the squash.

In all of the squash plots, I planted a Kousa dogwood seed, which needs a winter to "activate" it.

Next year, I could replant squash in my existing squash plots (which might then interfere with the Kousa dogwood which might germinate).  Or, I could make new 2x2 and 3x3 plots in the vicinity, and plant squash seeds in both.

But one trial is not useful to draw conclusions on.  So, "next year" needs to be part of this story.

I hope all of your gardens have done better than mine.  

I doubt that there will ever be a significant study done on companions simply because no one person would be able to do all the trials to be able to have a definitive work.
Then there is the problem of how each plant interacts with the fungal network, the soil food web organisms, the higher organisms effects upon the plants, fungi, bacteria and then there is mineralization to consider as well.
When there are so many variables, it becomes nearly impossible to select what you are going to study, then you have to devise a methodology that will give unbiased data returns that are hopefully repeatable for verification of the initial data.
All this while keeping in mind that every extra interaction will bias your data so you have to devise how you are going to neutralize those extra interactions since trying to document everything that goes on in a soil, microbiome, plant interaction would most likely having you pulling your hair out.

Many lay people don't seem to understand just how hard it is to separate things so we can find out how one particular item works, many experiments that have been devised to study plant companionship fail, mostly because of the inability to separate the function that is being wanted to study.
What happens to folks that aren't at the Masters or PHD level is what I've heard called the swarm effect, where the parameters of the experiment hits a sort of snowball effect, the more you try to pare away those parts you don't want to study or can't study the more critical to success those parts become.
If you do have funding, those supporters want to see your progress and results, if you are lucky you weren't given any directive of what they expect you to prove, find, support with evidence.
Over 90% of all scientific studies start out to prove something or achieve some given result, and the folks laying out the money expect you to show their preconceived results, or they go find some "scientist" that will slant their study to provide those desired results.
This is what happens in the Agri business all the time, look at any study by any chemical company and find where their scientists found that product X, Y or Z was harmful to those people applying the product, you will not find one case where that happened.

There are foundations that actually support good science, but they have to be very picky about which projects they fund because their pockets aren't endless.

Redhawk

Good day Bryant, et al.

I have background in both statistical mechanics and geostatistics.  I really prefer comparing data to theoretical models, as opposed to machine learning where everything including the kitchen sink is thrown in.

There seem to be some "obvious" things to companion planting:
1. Plant fennel by itself
2. Juglones inhibit most other plants.

But even within Juglones, typically the worse is black walnut.  But are there consistencies in the other Juglones?  

One set of relationships I have a problem with, is the differences between pole beans and the non-pole beans (runner beans? bush beans?).  Sorry, not enough coffee today.  If there is significant difference between those two kinds of beans; why is this not sufficient to split that family into two subspecies at that point?

hau Gordon,

Black walnuts aren’t the only trees that produce juglone, composed of 5 hydroxy-1, 4- napthoquinone.
Hickories (Carya) and butternut (Juglans cinereal) are also to blame, but black walnut trees are known for having the highest concentrations.
Juglone is released from virtually every part of the tree, although the roots, nuts, and seeds are the most toxic.

This site has a very comprehensive list of trees, shrubs and vegetables that can tolerate Juglone toxin and thus produce you a crop. (you can grow far more than most folks think)
PSU.EDU

When it comes to pole beans Vrs. bush beans, there aren't really many differences, it is very much like indeterminate tomatoes Vrs. determinate tomatoes, the difference is plant growth characteristics over all else.
You can plant both bush and pole beans right next to each other and they will play nice with each other.
You can start a patch of sweet corn (or any variety) then add in pole beans and surround those pole beans with bush beans and then you can add some summer squashes once the beans are growing well.
This is the traditional 3 Sisters method of planting. By the way you dig a hole, plant a fish, cover that with soil then plant the corn seeds, one fish per two or three corn seeds.
When you plant the beans around the corn stalks, the beans will use some of that planted fish for nutrients along with the corn, when you add the squash, again the planted fish provides nutrients to all the plants of the 3 sisters.

We try to plant like kinds in our garden beds that are going to root vegetables, just a foot or two of separation works quite well for beets, carrots, radishes and fennel.
We have grown these in the same bed several times with no problems at all (which makes them companion plants by the current definition)

Redhawk

If you don't do any programming, this comment may not mean much.

I am working in Perl.  I am using Perl hashes for the ad hoc databases.  I have now entered 4 usefully large databases of data (making some corrections or additions where I think I need to), and I've found a 5th which looks useful.  But, I thought it was probably time to start seeing if Perl would parse the file.  As I have entered this data, I have made decisions and sometimes changed decisions along the way.

For example:
1. the common name of the plant is maize, not corn.
2. the common name is bean/pole, not pole beans

and so on.

This file is basically just a database definition, with the idea of merging all of these into 1 database at some point.

There is an improvement on MLDBM a long time ago, which could freeze/thaw a perl structure into a SQLite database.  That could be one approach to use here.  Or, I could try to regularize the structure, and just use SQLite storing SQL.

For any given "common" name, the data includes the full biology nomenclature (as I understand it).  I am reading in 4 (more) sources of data, and I only put in the data for maize (Zea Mays) once.  I can replicate that data when it is missing.  I think a person also needs to include as much nutrition information as one can, if the USDA Nutrition database has data on the plant in question.

As people still argue about biological classification, it would be nice if there was a graceful way to just say that "this" common name is 0xABDFEF84.  Where the made up gobbledegook I made up, is say the SHA-512 hash of a particular version of the classification of that plant.  Perhaps BioPerl has ways to do this, I haven't tried to do much in BioPerl - I just know it exists.

In the case of nutrition data, I think there must be a way for USDA to update things, and so one should make a call from Perl to just fetch the entire USDA entry.  Hence, to actually use this, people would need this companion data and the USDA nutrition database.

This is still just a toy of a biological database, and it is over 10,000 lines long.  And that is just basically to create a SQL database or two.  A person still needs to actually write something to let people pull out the "companion data" (which includes anti-companion).

There are people in Permies who are doing there thing commercially.  That's fine.  What I do here, will be basically the common licenses of things on CPAN (Comprehensive Perl Archive Network); which is typically the user's choice beteeen The Artistic License of Perl, or their choice of the Gnu Public License.

So, how does Permies want to handle a database, or Perl source code?  Do I really post an X thousand line Perl source file as a comment?  Am I allowed to attach a SQLite-3 database file?

Gordon Haverland - did you make your database? Could you post a link?