Don't count on lists of "companion plants." Just like with medicine, people Back In The Day recommended a LOT of things in gardening with no proof. I always see huge lists of supposed "companion plants", but with no references to any genuine research (or anything for that matter), and not even any REASON why they MIGHT work.

The only claims you can count on are plants that are claimed to attract wasps or bees, and maybe plants that act as trap crops, though even with trap-crop plants I still don't see any references to genuine research. Indeed, if a plant is a good host for a certain pest, then maybe having it in your garden doesn't distract pests, but just attracts more!

One thing I did manage to find is that marigolds do actually put a chemical into the soil from their roots that is toxic to a lot of kinds of nematodes that can be pests.

And of course it is likely that alliums repel pests (if I'm not mistaken, the purpose of all those stinky/tasty compounds in alliums is to repel pests - I mean they even use them as an organic pesticide - though on the other hand those compounds only go out into the air when some part of the plants is injured)

Take everything with a grain of salt/be skeptical

I agree with peanuttree. I have done a ton of research both personally and by reading the experiences of others. What did I find?? Most of the results are anecdotal. Someone had less/no of this bug or that disease when they planted marigold. Well someone else right next door planted marigold and they had an abundance of this bug or that disease.

Best bet from my experience and research - GOOD SOIL!! Condition your soil with good compost, worm castings and composted manure is great!! Proper nutrients (get a soil test) and you will have LESS disease and insects. Notice I did not say NO disease - just less. How much less?? No one can tell you that.

I am not a total organic grower because when pest/disease gets a head start it is hard to stop it. I spray when needed and I decide when I need to spray. When you only grow 10 tomato plants it is hard to loose 5 plants to insects/disease.

BTW that was an interesting article.

DL

I'm going to agree with your other responders, Anney. But, the basis for my thinking is anecdotal as well - tried a few things; they didn't seem to work. It's good to see that some gardeners are actually doing side-by-side comparisons with companion planting. Somehow, given the concept, one might have thought that more of this sort of experimenting would have been done.

It should be wonderful if we could just keep the bugs OUT!! They can go off and eat some weeds! I've wondered if spraying beer on the weeds would encourage the slugs to eat them . . . never mind . . .

About the potato bugs - they like the deadly nightshade growing around (never in, perish the thought ;o) my garden. In fact, I'll notice them on the nightshade before they show up on the potatoes or eggplants. Lesson here - keep the bugs' favorite weeds out of the garden!!

And, that has always made me wonder about trap plants. Why the heck would we want to grow a nice healthy crop of bugs!?! So they can cross the aisle and attack plants that we really don't want them to eat? Its all a mystery, I've never grown a trap crop. I suppose you could get 'em all in there and then set fire to whatever-it-is they find so attractive!

Back to the companions, I've read a scientific study that concluded that some plants benefit while the other plant is not-too-inconvenienced by closeness of planting. That makes quite a bit of sense to me but the issue studied wasn't repelling insect pests - just productivity.

Tuff to sit back and say, "Yeah, well Mr. Bug we'll just see how long you'll eat on my favorite potato cultivar before you get sick of living beside that horseradish plant!" One thing for sure with horseradish - - it'll be back next year and forever even if you've completely given up on growing those Yukon Golds.

Steve's digits

I tend to believe that the very best defense is extra healthy soil with good humus, good bacterial action, good fungus, good worm activity, and nutrients released by those things. It seems that nature uses diseases and pests to weed out the unhealthy. I am not saying one would have zero pests and diseases, but only small amounts.
I believe that the health of the human body is simular to plant health. The very best protection is vitallity from the inside out rather than popped on drugs that don't work in full harmony with nature.

Has anyone tried so-called "beneficial nematodes"? I gave it a whirl, but the stuff I ended up buying was both expensive and dubiously packaged, with simply awful instructions, and so I have no idea if it would work, if I knew what I was doing and was able to get cost down (and to get the stuff from a more reliable source).

I have been an organic gardener for over 40 years. In addition to building healthy soil, I've found that having a range of flowering perennials near or in a vegetable garden attracts an enormous number of beneficial insects. The more beneficial there are, the more the total ecology of the garden improves and balances out the pests.

When I first moved to the property I now live on, 12 seasons ago, the soil was so poor hardly anything grew well--veggies or ornamentals. And the insect pests were something else. But as the soil improved and the ornamental garden began to flourish, the insect pests diminished to be replaced by an enormous range of beneficial insects. Whereas once I had to resort to all sorts of organic sprays against aphids, potato beetles, bean beetles, I find that now I have to really worry only about squash bugs, which I hand pick, and even they have really lessened--from over 50 per hill to maybe 10. I do, of course, use row covers extensively, especially on cole crops.

I do think that an organic vegetable garden with no blooming annuals or perennials of the right type is fighting a hard battle. Organic Gardening magazine once ran an article on the best flowers for attracting beneficial insects. I'm sorry I didn't save it, but among the flowers mentioned were those with flat heads like dill, yarrow and fennel. I have my veggie garden surrounded by groundcover thymes (they are the pathways) and beyond that on two sides are the ornamental beds.

BTW, I too have never really seen any effect from companion planting (or planting by the signs for that matter).

I am in agreement with comments above... the single most important thing you can do to reduce pests, in my opinion, is provide healthy soil. It is not often mentioned that most plants _do_ have defenses of their own; what we consider to be "flavors" are often chemical defenses against insects. Provided that the plants are healthy enough for those defenses to be effective, they can often fend for themselves.

Cucumber beetles, for example, are attracted to compounds given off by plants under stress. This could be caused by disease, inadequate water, or previous attack by other insects - such as squash bugs. Given a high organic matter, pH-balanced soil with good drainage & adequate water, plants are healthier & less attractive to the beetles. While there may still be some present, their population is considerably smaller.

The second thing, as mentioned by Lacyvail, is to create (or at least not discourage) a local ecosystem that encourages beneficial insects. It has often been mentioned by those who purchase those insects, that it's hard to keep them around. To do so, you need to provide a food supply for all points in their life cycle. A wide range of flowers, with long or overlapping blooming periods, is helpful. In addition to perennials _near_ your vegetable garden, plant annuals _in_ the garden. And for the larvae - which represent your true resident population - you might need to learn to tolerate enough of an aphid population to sustain them. If you are accustomed to killing off your aphids early, you might be inadvertently destroying the next generation of ladybugs & lacewings as well. For severe infestations, it might be more effective to go after the ants (which usually spread the aphids) rather than the aphids themselves.

There may be some truth to companion planting; I rotate all of my vegetables each year, and have noted some good combinations (such as beans & Swiss chard). There are also some plants that don't play well with others, such as okra. If your garden is high-intensive/high-density, then it is more important to know which plants _do not_ grow well together, than it would be with conventional methods.

But I think that for the most part, the issue is not which plants grow with which - it is to grow as wide a range of small plantings as possible, as opposed to large blocks. Large blocks of anything (mono cropping) promote the easy spread of insects or disease, and provide a stronger scent trail for flying insects to follow.

When I began saving seeds seriously, it forced me to alter the way that I gardened. If I wanted pure seed, I had to provide space & barriers between different varieties. This meant that my beans & tomatoes, for instance, could no longer be grown together in one place, but were spaced out in different "cells" throughout the garden. In any form of experimentation, there are often unexpected results... and in this case, the fringe-benefit was an enormous reduction in insect damage. This is not to say that I have no damage - only that it has been reduced to the point of being (usually) tolerable.

One last note... to encourage greater soil fertility, about 10 years ago I began to leave clover alone when weeding. I would still pull it out if it was directly in a row, but in paths & between rows was OK. After years of this, I now get a good stand of clover in the garden. When rabbits get in (as they always do) they prefer the clover in the paths to almost all of the vegetables. I guess that makes it a "trap crop" for rabbits. ;-) Only when I began to grow soybeans did I find something they like even better (and "like" is an understatement).

I do think that marigolds keep pests away and that garlic is a good deterrent for Japanese beetles. Not that either is perfect, but that more would come without them. Bugs seem to flock to whatever they prefer best; they seem to attack evening primrose (Oenothera), then brambles (blackberry, then raspberry), and between that and the garlic and scattered planting that seems to have caused them to leave the basil alone though they ravaged the basil my first gardening year, when I didn't have those other plants. Tansy and the like are supposed to attract beneficial insects, though I haven't tried that yet; my flower bed seems to bring in plenty of pollinators.

All anecdotal, to be sure. I don't know if leaving out all the alliums and marigolds would make any difference, and since there's so much variation from one year to the next, the only way to conduct a controlled experiment would be to plant identical gardens a few hundred yards apart and see how they fared.

Companion planting has never worked for me. Beetles devour stuff right next to garlic and trap plants just attract more bugs to the garden.
What works is row covers. And they work great. I cover squash to prevent squash borer and squash bug, cole crops to prevent leaf hoppers and aphids, carrots to prevent root maggot - the uses are endless. It has to come off of plants when they need to be pollinated but by that time the squash bugs and borers have generally given up and attacked someone else's garden.

oldroser

I've just purchased row cover material for my potatoes. I plan to grow them in seventeen 15"-diameter buckets in a raised bed. Each bucket has a hole in the bottom and the open end will face the sky. The potatoes can develop in the bucket with the roots in the earth. The buckets will be easy to add mulch to as the potato plants grow.

I am thinking seriously about making the row cover fabric into top covers for the buckets, sort of like those elasticized lids you see for kitchen containers. I thought I'd use strong twine to run through the hemmed bottom that will extend a few inches down the sides of the containers. The twine would be tied around the outside of the container under the lip that would keep this "hairnet" secured to the container.

Poor squash -- they get it coming and going. I guess I'll just drape some of the rest of the row cover fabric over my squash plants when they're young, which I'll put in other containers on the deck. And I hope you're right -- that by the time the blossoms begin to open, I can remove the cover and not have to worry about insect damage.