Anything that is remotely connected to organic gardening seems to qualify as companion planting. And that is one of the problems with this topic. There is no single accepted definition. This definition narrows the scope and excludes things like growing a cover crop for a better future yield, intercropping to maximize use of space, and using raised beds. Apparently some plants prevent others from growing properly. Walnuts and tomatoes are a classic example of this. Fennel does not seem to get along with anything, except dill — who know?
The above definition talks about the good companions with no mention of the bad. None of the definitions I looked at included the bad ones, but everybody goes on to discuss them as if they are part of the topic.
Should this be called opponent planting? I like the terms good companions and bad companions, as in good bugs and bad bugs. There is also very little scientific evidence supporting the idea of bad companions. Some people talk about allelopathy, but most of the support for this is demonstrated in the lab and not in the field. For example, some plants are hogs when it comes to nutrient and water reserves. Think of the soil around Eastern White Cedars Arborvitae ; I think they would be bad companions for most plants.
It seems that many authors combine these two topics, as if one is dependent on the other. Or maybe it is that organic gardeners are more willing to believe all of the hype around companion planting? One thing is clear — the two topics are not connected since you can practice one without the other. You can garden organically and not use or believe in companion planting, and vice versa. There are numerous ways in which one plant may benefit another and the following sections discuss a number of these.
The examples given below are provided for illustrative purpose and not because there is necessarily scientific evidence to support them. The examples may be true or not, and some will be examined in more detail in future posts. A large shrub provides wind protection which might allow tall delphiniums to flower without wind breaking the flower spikes.
Is that a benefit for the plant or for humans? One plant is used to attract a pest, so that the pest leaves the other partner alone. My roses were hardly ever attacked until my Contorta died. I also grew Desmodium canadense , the showy tick-trefoil, and it was a Japanese beetle magnet. We can agree that certain plants attract a specific insect more than others. But will placing such plants next to other plants protect them? Or do they attract more pests to your garden and the neighbors garden benefits?
This is the case with Japanese beetle traps. They work because they attract and capture the beetle, but in a normal sized garden they bring in more beetles than they capture. I always recommend them to my neighbors. Plant A can modify the environment for plant B. The lettuce and tomato are such a combination since the tomato provides shade.
In the three sisters planting, the squash shades the ground so that fewer weeds grow, which is said to benefit the bean and corn. It is easy to understand and accept as fact that plants modify the environment. However, extrapolating this to conclude that the companion plant grows better is false logic. Many flowering plants attract pollinators to the garden which then go on to pollinate vegetable crops.
A big problem with this approach is that flowering plants also attract pests — they also want nectar. So is this a net benefit for partner plants? Certain plants will keep pests away, so if they are placed next to pest-attractive plants, they keep pests away from both plants.
It is claimed that aphids and white cabbage butterflies hate the smell of mint. The same is claimed for keeping ants away but that is a myth. The classic case here is growing legumes to provide nitrogen for their partners. This is a very common myth, but the reality is that as long as the legume is growing it adds very little nitrogen to the soil. There is no benefit to the partner plant. Once it dies and decomposes there is some benefit, but that does not meet our definition of companion planting.
Comfrey is commonly called a dynamic accumulator because its deep roots bring nutrients to the surface were other plants can use them. As discussed in Comfrey — Is it a Dynamic Accumulator? If plant A suppresses weeds, then plant B grows better.
Makes sense. But if plant A is not also a crop plant, is it not just another weed that you planted? It competes with B just like the weeds. Is there a plant that you can grow beside your tomatoes to make them sweeter? Apparently planting basil and tomatoes together improves the flavor of both. Now that might be interesting, but given the general biology of plants and their limited ability to absorb complex flavor molecules through the air or soil — I am skeptical.
If a plant grows better because of a good companion, then it might produce more flavor molecules, or more sugar, making it sweeter. Why is it that all herbs have this property?
Would insect behavior not be determined by plant biology as opposed to how humans use the plant? How exactly does the herb know which insect is beneficial and which is a pest? Seems like nonsense to me. So if I have a plant that is wilting because of a lack of water I can plant dill beside it, and my plant will recover? And it also cures mildew? If dill is this effective it should be packaged as snake oil.
Aphids are certainly a pest. How can one plant both deter aphids and attract them as a trap crop? It has to be one or the other — not both. It could also be neither. Most articles about companion planting are poorly done, and include no explanations or references to support their position.
Many just copy the same list over and over again, repeating the same nonsense. Consider the case of the bean climbing up the corn. Clearly the bean is growing better and is able to get its leaves up higher to catch more sun. One could conclude it has improved growth. Corn uses a lot of water and nutrients, so its root system competes with the bean for resources. It also shades the lower leaves of the bean plant.
What if the bean plant produces lots of growth but few beans? Is it still a good companion? Companion planting in a vegetable garden should really be defined in terms of productivity. Does the plant pairing produce more food than when the plants are grown separately?
In an ornamental garden it makes sense to define improved growth in terms of appearance; more flowers, better leaf color or less disease. There are certainly some cases where plants benefit from having partners. And there are other cases that are nonsense. Crop densty, ratio, and relative planting times all affect the way that companion species interact with one another and their environment. If it lacks references to scientific studies, it probably does not work.
In future posts I will look at some specific examples to see if there is enough research to support their use. Very few references considering the size of the book. What I am going to do is explain why certain partnerships are beneficial — and leave you to make your own call about the other claims you may encounter.
The benefits of diversity in the garden have been apparent since at least the s when Charles Darwin, naturalist and proponent of the theory of evolution, pondered the subject.
Makes sense, right? The members of a community need to take up different roles in order for the community to be successful, and this is true whether the community is made up of humans, or of plants. Darwin came to this conclusion through his own backyard experiments and observations of the natural environment, but also by reading about those undertaken by his naturalist predecessors. Much scientific research backs the use of companion pairings, showing benefits such as biological pest control, protection, support, and the sharing of soil resources.
For those of us who want to avoid or reduce the use of chemical pesticides in our gardens, biological pest control is a necessary strategy.
Biological pest control focuses on using plants and animals — instead of chemicals — to control pests. Even with chemical pest control, the goal is to keep pests from doing too much damage to our crops rather than eradicating pests altogether. Companion pairings can protect our crops by helping to keep pest populations low in several different ways.
One of the most visible ways companion planting helps to control pest damage is by attracting other insects — in this case, predatory and parasitoid insects that serve a beneficial purpose in the garden. Predatory and parasitoid insects not only target moth larvae such as imported cabbage worms and cabbage loopers , but also much smaller garden pests like aphids.
A study published in the African Journal of Agricultural Research in August compared the presence of aphid predators in a kale monoculture versus kale interplanted with companion species. These companions included African marigolds, dill, cilantro, and calendula. Easily recognizable ladybugs, hoverflies, and parasitic wasps will be your allies in pest control. While the larvae of these helpful insects often eat pests, the adult insects tend to feed on nectar and pollen.
Including a wide variety of herbs and flowers in your garden will supply insects with needed resources, increasing the overall populations of beneficial insects and pollinators.
Providing a succession of flowers from early spring, with bulbs , all the way to fall with fall-blooming perennials such as asters , will encourage beneficial insects to make your yard one of their top hangouts. A wide variety of bloom types, such as you might include in your native wildflower garden , will also attract a diverse assortment of beneficials. Other predatory and parasitic insects that can be of help in controlling pests include collops beetles, soldier beetles, long-legged flies, midges, damsel bugs, big-eyed bugs, minute pirate bugs, hornets, yellow jackets, spiders, earwigs , assassin bugs, ambush bugs, and praying mantises.
There are many different flowering plants you can include as members of your insectary, including lacy phacelia, coriander , cosmos , dill , buckwheat, alyssum, marigold , cowpea, white clover, fennel , mint , rosemary , and lavender. To learn more about growing a selection of some of these multi-purpose herbs at home, read our article on the top five Mediterranean herbs.
If your garden environment is a relatively blank slate and you need a little more help, you can purchase predatory insect adults or larvae to help in your garden. Arbico Organics carries many varieties of predatory and parasitoid insects.
However, for control of the vast majority of invertebrate garden pests, predatory and parasitoid insects will go a long way in your favor. To fight garden pests, it can be helpful to understand the ways in which they locate their host plants — and one of these is through their olfactory organs, or in other words, via their sense of smell.
Much of the traditional literature on companion planting relies heavily on fragrant herbs or alliums that are thought to cover up the odors of host species. Luckily for us, there is scientific literature to back this up. Researchers who conducted one study tried — successfully — to use French marigolds to reduce populations of whiteflies on short vine tomatoes in a greenhouse setting.
It was the volatile compound limonene in the marigolds that had a slowing effect on the whiteflies. Limonene diffused mechanically also helped. African marigolds also release chemicals from their roots known as thiophenes, which repel harmful nematodes. Another study was conducted to try using fragrant herbs rosemary, lavender, and basil to reduce aphid populations on sweet pepper plants in a greenhouse setting.
Rosemary had a protective effect against aphid populations when it was placed 18 inches from the sweet peppers. Alliums — garlic , onions, shallots , and leeks — are another type of companion plant commonly cited for warding off pests with their strong smell. A paper that dug deep into companion pairings confirmed this, and found that these garden buddies are helpful in repelling moths, cockroaches , mites, aphids , and flea beetles.
Authors of the same paper reported that numerous aromatic species can repel pests away from brassicas, including sage , rosemary, hyssop , thyme , dill, southernwood, mint, tansy, chamomile , and nasturtium.
Does this mean you can stop worrying about pests if you include fragrant herbs in your garden? Not quite. Just because aromatic herbs repel some pests does not mean all pests will be repelled. However, aromatic herbs will prove useful as part of your overall strategy to keep pest populations in check. And some of these aromatics will do double duty, attracting predatory insects as well.
Another way pests locate their host species is by looking for them visually. Using companion pairings as visual or physical barriers may be just as effective as aromatic barriers. A group of researchers from the UK studying visual deterrence found that pests were confused when their preferred host plant was surrounded by green foliage — even fake green foliage made from paper!
Forced to search harder for their preferred plant, many pests gave up, which resulted in fewer infestations. The key, though, is that these visual barriers have to be green. These researchers determined that crops surrounded with other plants were more camouflaged from pests compared to crops surrounded by bare soil.
Taller companions such as corn , sunflowers , sorghum, sesame, and millet have been used successfully as physical barriers to block pests from accessing targeted crops. Although sunflowers can present problems of their own — more on that later. Using barrier plants is also effective in protecting crops from disease spread by aphids, as evidenced in a paper published in the September issue of Virus Research. In contrast to polycultures, gardens or agricultural areas containing a large diversity of species, monocultures make life very easy for pests.
This technique concentrates the pests away from your main crop. Rioux and will be eternally grateful to her for teaching me about it. Interplanting is a common sense way to garden because monocultures tend to concentrate the smell of a given plant, attracting its enemies.
Interplanting, on the other hand, dilutes plant odors and can thus help confuse predators. For example, back when I used to grow my potatoes in rows, I had major problems with potato beetles, but now that I mix them in with other vegetables, potato beetles are no longer a problem.
Some plants give off toxic products that inhibit the growth of their neighbors. Nor would I ever consider planting vegetables under a walnut tree Juglans spp.
Again, this is common sense planting. Riotte, gave such mixed results when I tried to practice it that, basically, I was just wasting my time. I get the feeling some authors are simply too embarrassed to bring up the subject!
His point of view exactly reflects mine: there are as many misconceptions as good gardening practices in companion planting, if not more. So, yes, I do practice a common sense form of companion planting, but am no longer blindly following Ms.
Not everyone will agree with me about this and if you want to say so, go right ahead. Your opinions are always welcome. Reblogged this on Sustainable Food for the Globe. Pingback: Do Marigolds Help or Hinder?
Email Address. Companion planting chart: often more confusing than helpful. Marigolds are supposed to repel root nematodes… but what root nematodes? Common Sense Planting Common sense planting: mix up your veggies and give each the conditions they prefer. Like this: Like Loading
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