What is companion planting?
I have read and experimented with a lot of companion planting ideas over the last 28 years of gardening in southwest Idaho. Companion planting is the term for deciding which plants to grow close to each other and why. There are 7 main areas of concern:
- chemical interactions
- shared pests
- shared diseases
- pest deterrence
- cross pollination
- space utilization
Understanding the ideas behind companion planting
Chemical interactions has to do with how a neighboring plant might affect the local soil. For instance, sunflowers are thought to inhibit germination of other seeds, broccoli is said to be bad for tomatoes, and cucumbers are apparently don’t like potatoes.
Pests, either insect or animal, will have to work harder to get their meal if they have to travel farther between plants. To take this to the extreme, one could intersperse all the plants in the garden. This could give you more time to problem solve and save your crops.
This is the same strategy for separating crops that are affected by the same diseases. How well crops can be separated will depend a lot on how large the available garden space is. An example of being careful of shared pests is radishes and cabbages, which are actually considered to be in the same plant family, but since we eat different parts of them, it might not be obvious. If you compare the leaves, you can see the similarity.
Pest deterrence is slightly different, in that the companion or interplanting is meant to specifically use one plant to keep a pest away from another plant. It might be by repelling the pest, camouflaging one of the crops, or enticing the pest to another plant. For instance, scented geraniums are said to repel cabbage worms. Beans and potatoes may protect each other from the main threats of the Mexican bean beetle and the Colorado potato beetle.
Cross pollination is only an issue if you want to save or eat the seeds. It can be avoided by both adequate space between similar crops or timing their maturity. In my neck of the woods, there is not a long enough warm season to adjust the planting time, so I avoid cross pollination of corn by choosing varieties that mature at different rates. This gives me some earlier corn to enjoy.
Not all plants use space the same way. Some grow more underground, some vine straight up, and others spread considerably in the space above the soil. Picturing how a plant grows can help when deciding how well crops might share space or how closely they might be grown. This could incorporate the idea of succession planting. Some plants can be trained up a trellis even if they would do just as well on the ground. Cucumbers and tomatoes fall in this category.
Sometimes companion planting is at least partially a matter of aesthetics. A row of purple bush beans can look quite nice in the flower garden, as can hot peppers, and even cabbages. There is sometimes room to grow flowers among vegetables, as I talk about doing more of last year (video tour included).
Does companion planting really work?
Not all that you hear about companion planting has been verified or will work in a given environment. Here are a few things I have discovered along the way:
There can be trouble with growing conditions, i.e. nasturtiums like afternoon shade in southwest Idaho, which makes it harder to grow them next to plants that need full sun as pest traps. Watering during the heat of summer in southwest Idaho can be tricky sometimes. Not all plants can take the intense, dry heat.
Some plants recommended for companion planting mature at different times in given environment. Here in Idaho, the only way to grow peas for eating (as opposed to a seed crop) is to plant them early in the spring. They will not grow well at all if planted at the same time as warm weather crops, so all the companion advice about growing them with corn or cucumbers is not much use here.
Some trap crops are rather invasive, like mint. Grow mint in your main garden bed at your own peril. Unless you are very diligent about taming it or keeping it in containers, it will overrun the rest of your garden and it is not easy to weed out.
Not all varieties of a crop grow to the same dimensions so it can be unpredictable how much space they will take up. I have grown zucchini plants that spread over several square yards and I have grown some that stay fairly compact (Black Beauty). This can affect not only how much sun and nutrients neighboring plants are getting, but you can end up with plants closer than you intended. Of course, pruning is usually an option and can even channel more energy to ripen fruit in a timely manner.
Keeping track of dispersed crops can be challenging. It is much easier to monitor maturity and harvest efficiently if plants are close together. Also, harvesting food from your flower garden may leave holes in the landscape. These may fill in as other plants are eager to fill the space, or you could do some succession planting.
There may not be enough overall space in a home garden to make some companion planting worth the effort. If you only have a couple of raised beds right next to each other, nothing will be very far away from everything else. Keep in mind that it is a rare year when every crop will do well, so don’t be too quick to come to conclusions. Remember that sometimes the information about companion planting has been passed on for no good reason.
Resources on companion planting
Many universities have agricultural departments that do research on things like this. When I do a web search, I look for the reports from people like Linda Chalker-Scott and her paper titled The Myth of Companion Plantings, which helps to put things in perspective. This article called The Truth About Companion Planting seems balanced and practical, too. Even with that, I take their research with a grain of salt, since I know how hard it is to set up a study that can isolate factors.
One book I have had for a long time is Carrots Love Tomatoes. It gives a lot of suggestions, but it doesn’t give very many reasons for me to evaluate. However, it is simple to read and I use it as a starting point.
I have referenced gardenmyths.com several times for evaluating popular remedies and claims. I could only find one article on companion planting there (marigolds and nematodes), but it gives you a flavor of how something that is so pervasively believed might not really work.
It is worth experimenting with combinations. The particular conditions of your own garden may give you options that aren’t listed in books or experienced by gardeners in different climates. And even though university scientists may know lots of things, that doesn’t make them always come to the correct conclusions. Call it whatever you like, there can be advantages to planting in various combinations and successions. What matters is that you are happy with your gardening,