Recently, I finished reading a book by Jessica Walliser called ‘Plant Partners’. The book’s focus is on science-based companion planting in the vegetable garden. While many gardeners routinely practice companion planting, the science of why and how it works has not been well understood. Yes, many of us plant marigolds and basil around the garden. But how do these plants interact with other plants in the garden?
This post will focus on companion planting in the vegetable garden for pest management. We all likely have a pest that we cannot control in the garden. For me, it’s the cabbage worm in Cole crops such as broccoli, cabbage, and kale. As an organic gardener, I routinely use row cover to protect the crops. However, when the cabbage worms get out of control, I apply an organic treatment of Bacillus Thuringiensis (Bt).
Now, with a scientific companion planting approach, there’s another tool in our gardening toolbox. As with most things in gardening, having an intentional approach allows for evaluation and adaptation. What do I mean? Well, as mentioned, I always do companion planting but without the knowledge of ‘why’. Without a ‘why’, it’s hard to judge the success of any given strategy. Let’s take a closer look at companion planting in the vegetable garden.
Intercropping is another way to describe companion planting. With intercropping, there are multiple strategies that can be deployed. First a definition. Intercropping is the planting of more than one plant within proximity to other crops for an intended biological effect. The benefits of intercropping include the following:
Besides benefits, here are the strategies that can be deployed with intercropping.
The above sounds a lot like companion planting. Well, companion planting is really the same thing as mixed intercropping. Most home gardens use this form of companion planting. I will, therefore, focus on mixed intercropping in the home garden.
Plants are rather amazing when you think of the ways they have adapted to persevere. Mostly, plants protect themselves via chemical compounds produced by the plant itself. Furthermore, plants protect themselves by emitting a volatile chemical into the air. This volatile chemical can either warn neighboring plants about insects or attract predatory insects to feed on leaf-eating pests.
Lastly, plants can modify the chemistry of the soil through the production of root exudates. These root exudates can make conditions either better or worse for other nearby plants. Certain plants are known as allelopathic plants. Allelopathic plants release chemicals that can inhibit the growth of other plants (such as weeds) or act to repel insects. For example, sweet basil releases oils into the soil and these oils act as an insect repellent to both basil and the plants around basil.
Therefore, knowing about and understanding the impact of the chemicals released by plants informs our choices with companion planting. For example, it’s commonly understood that the odor/fragrance emitted by marigolds is a deterrent to insects. However, there is no science to back up this thinking. Yes, marigolds are a deterrent to pests by not for the reasons we initially thought.
Let’s look at the science of broccoli interplanted with marigolds. Marigolds mask the cues that pests use to find broccoli plants. Thus, marigolds act as a pest deterrent for broccoli.
To better understand this phenomenon, we need to understand how insects find plants. There are three ways that insects find plants.
Mixed intercropping allows us to interrupt these visual and chemical pathways.
In this section, we will look at several combinations of mixed intercropping that can have a benefit on the target crop being protected. Scientific studies have found these causal relationships. However, you may have a different experience in your home garden. Therefore, it’s important to observe and keep notes on any impacts.
A further note about marigolds. French marigolds have been shown to alter the chemical profile of the target they are protecting. They do this via the interaction of underground roots. Marigolds produce root exudates that are then absorbed by the roots of the neighboring plants. Thus, providing insect protection. How amazing!
Some companion plants act as a visual barrier. For example, growing dill or corn can act as an insect barrier. Because of their height, they visually camouflage the target plant and impede insect movement. Sunflowers can also act as a visual barrier.
Another method of managing pest populations is to plant flowers that bring natural enemies into the garden. In this case, the flowers act as biological control. Creating greater diversity in the garden will naturally create greater varieties of prey. Companion flowers act as both a food source (pollen and nectar) and shelter to natural enemies.
One study showed that when dill was interplanted with eggplant, there were lower populations of the Colorado potato beetle. In this case, the flowering dill plants encouraged more natural enemies of the Colorado potato beetle.
Understanding the science behind companion planting in the vegetable garden is an amazing area of study. Because most studies are conducted on large farms, adaptation to the home garden may take some trial and error. What we know for sure is that having diversity in any garden is better than a monoculture (single species of plant). This year, I am thinking differently and will focus on mixed interplanting in each of my vegetable beds. Give it a try and remember to record your results!
Here are a few posts that may be of further interest.
When you’re looking for guidance on companion planting to improve your organic garden, it’s likely that you’ve come across a vast array of charts. Companion planting charts tell you which combinations are supposed to work together, but they don’t typically tell you why these particular pairings are recommended. So, how do we know these partnerships actually work? That’s what we’re going to dig into here. I’m not going to try to
The home gardener has several ways of irrigating the garden: a watering can; a garden hose with a fan nozzle or spray attachment; a portable lawn sprinkler; a soaker hose; or drip or trickle irrigation. Most of these options are simple to use and work adequately. While drip or trickle irrigation requires special equipment, it is the best method to use for conserving water. A drip irrigation system is the best method for conserving water in the vegetable garden.Barbara H
Im not embarrassed about it. I admit that the way my vegetable garden looks is just as important to me as how much food it produces. I keep the rows straight and well-weeded, and the paths are mulched with a thick layer of straw. Plants are arranged so their foliage and fruit can be easily admired. Fortunately, when it comes to the vegetable garden, theres no need to sacrifice function for aesthetics. Our display gardens here in Burlington, Vermont, have timber-framed raised beds, wide, bark-m
Summer squash does everything but plant itself. If you seek a vegetable that is easy to grow, flavorful, and nutritious, look no further. You can help summer squash thrive by planting it with companion plants.If you have planted zucchini, pattypan, longneck, or yellow crookneck squash, you know what vigorous growers and prolific producers summer squash can be. Summer squash (Cucurbita pepo) is ready for harvest in as little as seven weeks from planting.Squash, one of the olde