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Why Companion Planting Works (The Science Behind The Magic)

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Companion planting or interplanting is a powerful gardening technique that I think confuses a lot of first-time gardeners. But if you think about it, it’s really been practiced probably since the dawn of agriculture itself. Think about something like beans and corn. Pole beans need something to climb up. Corn provides that stalk and also sort of protects those beans. Then you add something like squash to ground cover and sort of shade that entire system.

And voila, you have the three sisters method of planting that indigenous Americans came up with so many years ago. But while some combinations are intuitive like that, or maybe something like tomatoes with flowers so that bees come by and help pollinate the tomatoes, there are some really science-based companion planting ideas that are somewhat counterintuitive. And that’s exactly what we’re going to talk about in today’s article.

Protective Mechanisms in Companion Planting

So, as an example, think of the rose arch. It’s tempting to the eye to think, wow, this plant’s just kind of blowing around in the wind. It’s not doing anything, but that couldn’t be further from the truth. Not only is it actively growing at all times, but it is actively trying to protect itself from would-be predators. Take roses, for example, if you take a closer look, you’ll see some thorns climbing roses. That’s going to dissuade pests from chomping down on those canes.

It’s going to dissuade little rodents from maybe building a nest or, or a bird from building a nest. And honestly, even myself I’m going to have to strap on some pretty heavy duty gloves if I want to prune that rose and be safe. But it is not only visible mechanisms that plants use to protect themselves from pests or predators.

Weed Control Through Companion Planting

Believe it or not, some plants can actually inhibit weeds on their own. They don’t need you to come in and spray. Cucumbers are actually a great example of that to the point where a good combination is taking cucumbers and putting them in between your tomatoes in your summer tomato garden. It’s kind of funky, but they actually produce allelochemicals which inhibit weeds and other seedlings. And notice I say other seedlings, which means other edible stuff that you might want to grow might not be a fantastic idea to plant right next to a cucumber, not only for the inhibition effect, but also because they’re going to produce all of these leaves that are going to block light that will also inhibit weeds. So you can think about these combinations that are a little counterintuitive, but produce an interesting result.

When looking at planting for weed control and these interesting companion planting ideas, looking at farmers is often a good indication, especially if they’re organic farmers, because they make their living doing this. So they better be doing a good job. And speaking of, you get into this crop called winter rye. Winter rye has 16 chemicals that are known to inhibit seed germination, but only at that stage. You can actually put in a large tomato and it’s going to be completely fine. So a lot of farmers put winter rye in in the winter, let it grow and then chop it down. And it inhibits most of the common weeds that they’re going to experience. Something like foxtail or purslane. So it’s something that you could think about sprinkling in your rows.

Utilizing Trap Crops for Pest Management

The name is very self-explanatory. One of my favorites is nasturtium. They can sometimes suck up the attention of unwanted pests that might attack your brassicas like an aphid or something like that. But another interesting idea is if you suffer from flea beetles, which might be hitting your tomatoes in the summer, you can plant radishes or pak choy near them. Flea beetles tend to like those a little bit more and they will sort of attack those and leave the plant you actually want to grow a little bit more intact. So it’s, it’s a little counterintuitive. You’re planting something edible that you want less around the thing that you want more, that the pest also wants more. So flea beetles, pak choy and radish are a good combination.

Another one is taking tomatoes and putting cowpeas next to them if you’re dealing with something like a stink bug. If you see stink bugs all up in your tomatoes, throw some cowpeas down. They like cowpeas way more. They’ll go on over to the cowpeas. And then you can actually pick up and collect the stink bugs and extinguish them so that they don’t reproduce. So another example of a weirdly counterintuitive combo that serves the purpose of preventing a pest.

My favorite example of this trap crop idea is actually a positive one. And it’s taking alyssum, sweet alyssum and planting it next to things like tomatoes. Why? Not because a pest is attracted to the alyssum. It’s actually because the pest of a pest is attracted to the alyssum. A bracketed wasp really loves to be on and around that alyssum. But what it will do is it will find tomato hornworms nearby and lay its eggs in the back of the tomato hornworm.

A little gruesome, a little freaky, a little raw nature there, but it is true. And you’ll see these, these little white little balls kind of hanging out on the back of a tomato hornworm. That’s actually the eggs of the wasp, which will kill the hornworm for you. And then the larva of those eggs can destroy aphids, which of course can also impact your tomatoes. So not only does it beautify that combination, it’s a very pretty plant, very beautiful, but it has this crazy benefit of automatic pest prevention. Learn more about Companion Planting.

Soil-Borne Disease Management with Companion Planting

Some crops like brassica, and even more specifically within the brassica family, mustards have what’s called a biofumigant property to them. There’s a compound called isothiocyanate within this family of crops specifically, that not only gives it that bitter taste that we either know and love or know and tolerate, depending on your particular tastes, but it also helps control fungal diseases or soil-borne diseases like verticillium wilt or fusarium. So if you plant this or companion plant this with a particular plant that might suffer from it, it can help. But this is also why you see specific types of brassicas thrown into like a cover crop mix that you’ll throw onto a bed at the end of a season and just let it chop and drop. It’s because when tilted back into the soil, it’s really effective at controlling those soil-borne diseases. 

Enhancing Soil Quality with Companion Planting Combos

Some companion planting combos actually improve the quality of your soil, either the nutrient density of it or the texture of it. And one of the most famous ones is peas and bean legumes. What they’ll do is they’ll fix nitrogen. Basically they’ll take atmospheric nitrogen in the air and affix it to themselves. And then eventually when they die, it’s broken down into the soil. So it’s not as simple as just, hey, you planted some peas, magically there’s more nitrogen in your soil. So let’s talk about a couple of combinations that really work.

Utilizing Nitrogen Fixers for Soil Enrichment

So how do you use nitrogen fixers correctly in the garden? You’ve got things like bush beans, cow peas, and our personal favorite would be fava beans.

Optimizing Pollination with Companion Planting

What happens in the actual plant is that the nitrogen is fixed to these nodules that are around the root zone. So while the plant’s growing, yeah, you could plant beans and I don’t know, tomatoes at the same time, and there’ll be some level of additional nitrogen, but it really isn’t a ton.

It’s actually better to grow those plants ahead of the crop that you’re going to put in next. So beans or fava beans, especially since they like to grow during those colder months, when you cut them down, you don’t rip the roots out. You just can’t do that. Because of course all the nitrogen is in the nodules, which is in the roots. You can cut them down to the ground. Don’t rip the roots out.

Leave them in and then plant into that area. And then you’ll actually get some of that nitrogen fixation benefit. So if you’re looking for a very clear companion planting idea, you can take corn and fava beans. Plant fava beans then on the outside edges and on the interior. And then you could take corn after the fava have really started to grow and maybe gotten close to the end of their life and sow it down the middle. So they get to benefit from the fixation that’s taking place.

Maximizing Garden Productivity with Pollinator Attraction

A lot of gardeners struggle to get good pollination, maybe on their cucumbers or their squash. And this is where thinking of the garden not just as a place to grow your groceries is really key. I’ll be honest, when I first started gardening, I was like, if I can’t eat it, why the hell would I grow it? It makes no sense. But in fact, it’s completely the opposite. You need to be planting flowers of all different shapes, heights, sizes, colors, as long as they’re not invasive or harmful in your region, in your garden. And you can plant them in all different ways.

Conclusion

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