The first i saw something about radishes and cucumbers was in Fine Gardening many years ago and the Tip Writer said to plant an Icycle Radish next to your squash plants and that would help keep the squash bugs away. That has since been corrupted into radishes will repel the Squash and Cucumber Beetles.
Some people have remarkably good success with many aspects of companion planting while others do not. That some people experience failure with companion planting does not mean it does not work, only that there are other things going on that may not be very obvious.

I have never found specific plants to be very repellent. There are several recommended to repel CPB - which names I can't remember, and supposedly onion and marigold for ICM. Probably the problem is that we don't try them until the infestation is hopelessly severe.

Well, there are claims that marigolds are repellent to all kinds of garden pests, when in actuality they can be attractive to spider mites, thrips, aphids, and mealy bugs, to name just a few. So maybe a plant will repel some pests only to attract something as bad or worse!

I just wish companion planting worked for specific problems that are often cited.

I agree with you that some claims are written just to fill a page in a catalog or book and they really have no meaning at all. The only way for you to really find out what works for you is to try different things until you find one that works.

The best way I have found to raise healthy plants is to plant things that are resistant to pests and diseases. This also is a technique that takes a lot of trial and error. Varieties that do well in my area may not do well in yours or even someone who lives a mile from me. My soil, climate, gardening practices and temperament are not like anyone else's, so what is a tolerable level of loss to me may not be acceptable to you.

Finally, gardening isn't planting and reaping, it's mostly learning and patience for the first 50 years or so. By then I imagine you'll have all the proof you need.

Some companion plants are supposed to repel potential pests, some simply confuse those potential pests, and some are trap crops, they actually attract (Nasturtiums) the potential pest away from the plants you do not want them on. Marigolds, the non hybrids, have been reported to aid in controlling harmful nematodes in soils and a few people report they will repel some unwanted critters. The hybrids have those properties bred out of them and do not work. To successfully use companion planting you need to find out whether what you are going to plant is really what you want and will do what you want. Many years ago I saw a hint that planting an Icycle Radish next to a squash/Cucumber/melon would aid in warding off the squash pests and have seen that corrupted into any radish and that it does not work.
As seamommy states it takes time to learn about companion planting just as it takes time to learn about your soil and it takes time to make that soil into a good, healthy soil (simply dumping some kind of "fertilizer" on soil is not the way to do that) that will grow strong and healthy plants that will be better able to ward off insect pests and plant diseases.

Successful gardening has no single magical formula. It is a lot of small harmonies. Healthy soil is the foundation.

A soil test is a sound investment that enables you to assess your progress in management. pH levels and organic matter percentages are critical to establishing nutrient cycles and moisture mediation. Amendment decisions do require some guidance as offered in the test report.

What you plant and the rotation of plantings are equally important. Select suitable varieties and follow a 4-7 year rotation schedule. Companion planting is a simple reference to what grows well together. The inference here is to avoid large scale single plantings. Each of my wide (3') beds will see interplanted species. The simple moving of each planting from bed to bed makes rotation simple; in fact I move them at least two beds from previous year.

Companion planting does offer some advantages. Some of the matchings do mask or disrupt, a few in the blossom stage. Being able to avoid bad combinations is logical, especially if allelopathic interactions. It is a hard search to find the scientific evidence on the how and why.

Splitting the plantings of same family or similar pest/disease species seems logical.

The fact remains that stressed plants attract pests. A strong healthy plant attracts few; or at least does not invite egg laying. Likewise, a healthy plant is more likely if rotated from previous planting locations.

Some plants, particularly brassicas, will attract the pests regardless of solutions. For that reason I will always employ the row covers to block those pests.

The diversity of companion planting does a lot to attraction of beneficial organisms. The organisms are equally important above and below ground.

Recently I have been looking at the information on specific plant and root exudes. Plant and soil sciences are fascinating studies. Too bad they do not focus reseach on some of the prominent questions we see in this forum.

Rarely do you see a specific variety identification on any of the companion charts. Hopefully my own trials and rotations of heirloom varieties will give me some answers over the years.

Observation - I have found that blossoming radishes do attract more of the parasitic wasps.

Dan

Share that information when you're sure about it.

I find myself fascinated by research showing many plants, or some at least, defend themselves in various ways against insect pests and diseases that would damage them. Haven't seen anything about plant and root exudes though.

A lot has been written about gardening just to fill the page, as stated above. Remember a lot of garden writers don't really know much about gardening, except what they have read from other garden writers who don't know a lot about gardening. If it pays by the word, repeat! steve

Though not about OP question, one thing that I KNOW FROM EXPERIENCE is that radishes retard the growth of tomatoes - planted within 1 ft. And the retarding lasted through the life of the **tomato, even after pulled all radishes. Don't know if they would also affect other nightshade plants, but won't chance it. [** fellow 6-pack 'toms' planted further away from small radish planting, grew much larger and produced more fruit.] After I noticed the small size of the 'runt' tomato, I read a reference to this effect, and pulled the radishes.

g'day anney,

that is somewhat of a vexing question, and marigolds are supposed to repel nematodes, and garlic aphids, and basil and tomato's together supposed be good for the tomato? and the list goes on, for me i have never noticed the difference with or without companion plants, i've tried things earlier on now i don't bother do a bit of rotation planting a bit keep the medium well fed and bugs are not that much of a worry, and i plant my garlic or basil wherever there is room.

all you can do is try it if you have a particular problem to deal with, but as is said already don't group plants, plant randomly at least that way the bugs won't find all your plants, our best bug control is early morning safaris, the pick off and squish method.

len

Here is a link that might be useful: lens garden page

borderbarb

Thanks for the tip. Maybe Dan can look into that to see what about radishes troubles tomatoes.

len

I'm aiming for more garden randomisation this year anyway, but for those pests that get wafted in by the wind, I just keep my fingers crossed that they'll not devour whole crops! I have pretty bad arthritis so I'm not as able to do a lot of digging and pulling as I once could -- that's why I was so happy to get 25 bales of spoiled hay. I can spread them out and not have so many weeds to deal with. I'm hoping they'll help keep the nutrient and water supplies to the plants stable, and thus healthier plants.

I'm also spacing some things greater and planting flowers and herbs between the plants or between the small clusters of them with an eye toward confusing airborne plant pests.

It's been a couple of years since I've had any real problems with insect pests and am not too agitated about a few. But one year we were innundated with cucumber beetles, as my neighbor's 5-acre corn field is right adjacent to my garden, and he plants corn there year after year. They stay in the soil and are ever ready to munch on my garden goodies, too, as well as the others that come in on the blowing winds. Also a few Mexican bean beetles, which can really mess up your beans. You probably have insect pests that are worse some years than others as we all do. It depends on a lot of factors.

Anyway, hoping my gardening practices are shifting enough to make a difference even if the claims I've found on the internet don't hold water.

Below is a review about allelopathic plants. The many references can give you further reading.

The greatest challenge in research is the isolation of singular cause and effect. With so many variables in the natural environment it may require dedicated research using non-soil growing medium in an isolated environment. Suffice that there are so many reports of the effects on various crop that one can lean towards the effects being real; regardless of the inter-active causes.

Re: Radish - radish (Daikon) is a frequent cover crop variety. The weed control effects are good for a winter-kill crop. I shall see if there is a reference to the specific allelochemicals.

The rye cover crop is also a great example. As a green manure, tilling in can see allelopathic effect lasting several weeks. If untilled, the same effects will last up to 10 weeks. Decomposition rates are the factor.

Good reading.

Here is a link that might be useful: Ecological Effects of Allelopathic Plants a Review

While lists such as these are not PROOF of effectiveness, the fact that they have endured over generations is, at one level, a kind of PROOF THRUGH EXPERIENCE AND OBSERBATION.

Of course the 'beneficial' effect can be because of weather/soil conditions, or because they are hosts to good insects that prey on the bad ones, as much as from any other conclusion.

Here is a link that might be useful: Compatible/incompatible combos

Well I think I read all of this thread but I didn't see anything relating to plant height and root development which I've been trying to be more aware of lately when planning the garden.

The way I see it is that the more diversity of plants you have in your beds or fields the better. Instead of having 20 lettuce plants of the same variety grow 4 varieties 5 plants each and locate them in different areas.

The information that is available on companion planting is basically a rough guideline. Take that guideline and experiment a bit.

anney: I'm a bit skeptical about companion planting because I've seen conflicting accounts about the same companions -- none of which I can remember though. That said, I do find garlic a great companion plant. Somewhat off-topic, but relevant to "show me the proof" is Doug Landis's researh on plants that attract predatory insects. He is-or-was Michigan State University, and I'm sure one can google his study. I do remember that the top two are boneset and sweet alyssum. We have both in the garden and we have very few insect pests, just flea beetles, black bean aphids, Colorado beetles, and a few cut worms. Can't claim case-and-effect though. Regards, Peter.

I haven't found any companion plants to be so pest specific except the tiny marigolds that are used to control nematodes. That worked when I had a garden in south Florida, but they have to be the little tagetes (usually sold as Gem), not the regular French or African marigold. The Gems have a slightly citrusy smell.

IME, the advantage of companion planting is not that it keeps certain bugs away but that it attracts predators. I combine flowers, herbs, and veggies in my garden, not according to companion planting prescriptions but according to what I want to grow. The buggiest garden I ever had was one where I planted the flowers/herbs and veggies separately, as would be done in a traditional garden. I always mix them up now and have few pest problems, no evil eye. I have noticed that most companion plants have aromatic leaves and a lot of them are Umbelliferae (they have flat, umbrella-like groups of flowers, like dill, fennel, carrot, tansy, yarrow, and one I grow a lot, costmary). I think it is the smell of the leaves combined with the attraction of predators to the flowers that works. Most essential oils can work as pesticides, and most of the herbs and flowers recommended for companion planting are high in essential oils.

The other thing that I think is part of the mix is deliberately not monocropping. I try to break up something I want to grow a lot of into very small patches interspersed with other things. I think that large patches act like a beacon to insects that prey on those plants. I have also been experimenting with using a living mulch, like white clover, and this seems to really help a lot also.

When I look at companion planting guides, the first thing I look at is beans and onions(these 2 hate each other), If the guide says they are good companions, I stop reading that one.
I haven't had any problems with radishes and tomatoes grown together, the radishes do seem to attract underground bugs or worms that would normally bore into tomato roots.
I also plant radishes with squash, it did seem to help.
Potatoes and strawberries are not good companions either(found that one out last year, LOL).
I always plant beans near corn(they both do better).
I made a copy of this guide, it looks reasonable from my experiences. http://www.tinkersgardens.com/vegetables/companionplanting.asp

Don

I don't see where anyone has mentioned the fact that what may work in the north...may NOT work in the south. There are different pests as well as different grow cycle times, etc.
I was raised in the north (central Ill.) & now live in the south (SE Ga.) and lots of things are totally different than what I grew up learning.

Besides the fact that much research can be biased by who is paying the bill for it!!!

If you're interested, here's a beautiful "companion" marigold:
[Found outside an old Muslim school in Tashkent, Uzbekistan in 1992. This marigold is a favorite of flower seed collector, Bob Bell. Introduced in 1999 by SESE.] The plants are 12 to 16" tall, with a deep green dense foliage that has a sweet marigold fragrance. It lacks the common astringent odor of other marigolds. The plants are so fragrant they sweeten the air on a hot summer day. 'Tashkent #1' bears numerous 1-1/2 to 2" single petalled flowers that have yellow centers and velvet mahogany petals with a fine orange border. As the petals mature they change from mahogany red to orange red. This is the finest marigold that we have grown.

Here is a link that might be useful: French Marigold, Tashkent #1

Anney: there is the other approach also, trap crops. I once did some work for a commercial broccoli grower in western CO who was unhappy with the methods available to him for flea beetle control using the usual pesticides. It turned out that CSU had done research on flea beetle control in broccoli and other cole crops within 20 miles of his location at the turn of the 20th century. That research found that flea beetles had a strong preference for radishes when planted in proximity to broccoli. I suggested the grower try a field with a radish trap crop perimeter that he could easily spray from the ground using far less chemicals, he did and was very pleased with the results both culturally and economically. Boy was I surprised!

I found out, inadvertently, that buddleia, or butter fly bush is a very effective flea beetle trap. I've got 50 odd bushes around the yard and they get shredded by flea beetles every spring, but the garden stays untouched.

Unless I plant bok choi or Asian greens. Then all bets are off.

Geraniums (Pelargonium zonale) could help control devastating Japanese beetles:
http://www.ars.usda.gov/is/AR/archive/mar10/garden0310.htm

Here is a link that might be useful: Geraniums /Japanese beetle

I don't have a strong opinion on this, but an observation that pests tend to attack plants that are weak. Perhaps companion planting works best when the plants themselves are healthy.

White icicle radishes next to cucurbits works quite well. The trick is that the radishes must be flowering to confuse the beetles. I was very skeptical of this method before actually trying it and now I'm a believer. The difference from a bed without these radishes is night and day. Give it a try before you complain that it doesnt work.

I use companion plants to shade out weeds & to draw in pollinators.
I have few insect problems & only put down organic powder for ants.
Mostly Tomato horn worm & squash bug(sink bug) & I hand pick them twice a week.

Got a plant that works for me to keep whiteflies, etc. off tomatoes--in a greenhouse, no less! Never read about it, but it's called "shoofly!" (nicandra physaloides). It is easy to grow, pretty blue flowers & reseeds.

I planted shoofly in florida some weeks ago. It was just getting ready to flower when I left.

SoTX & pnbrown tell us more about why you think "shoofly" is a good plant.
I can Google it, but your "Experience & Observation" as borderbarb put it, is first hand.
Who knows what the talking heads on the net really know about anything.

jolj:

I ran across the name somewhere in my travels (no computer then) and was truly desparate after trying everything else, including STP. Then it was a matter of finding out what it was and who sold seeds.

It was working at 2-3" tall but no clue how. Not a trap crop. Tossed seeds in with the tomatoes with high hopes. Always a thrill when something actually works!

Sorry I don't have more information. I was looking for shoofly pie when I ran across it!

The "shoofly" disappeared without a trace. Maladapted plants tend to do that when faced with competition from bahia grass and hairy indigo.

Interesting tidbit about the white icicle radish. I have a lot of cukes going this spring, and by coincidence some white icicle, though they are not near each other. I think white icicle must be near the wild form because it is really a terrible eating radish.