Just like humans, most plants are happier if they enjoy their neighbors. Companion planting is the artform of creating a plant community where neighboring plants benefit each other. In this article, we will share the best companion planting for tomatoes, potatoes and brassicas.
Why companion planting?
There are numerous ways in which plants can benefit one another:
- They can give each other a chemical or nutrient boost, like legumes who fix nitrogen in the soil.
- They may provide structural and functional support, like shade or ground cover to retain water.
- Finally, they can importantly influence insect activity. If a harmful insect doesn’t like the smell of an aromatic companion plant, it will stay away from your crop. If a beneficial insect, like a pollinator, particularly enjoys the companion plant, it will head on over. While it pollinates its favorite, it may decide to check out your favorite.
The main reason to consider companion planting is that it can bring you better harvests, and it can do so organically and affordably.
By promoting everything mentioned in the previous paragraph, companion planting naturally leads to stronger plants. The pest you felt you needed to spray before is now naturally gone. Goodbye pesticides! The boost of nitrogen that a plant needed is now naturally provided by its neighbor. Goodbye fertilizers! Everything works for everything, letting you work less.
Some gardeners are skeptical of the validity of companion planting. It is understandable. Because when you search on the internet or in books, you can find charts and articles with contradicting information. Also, there is simply little explanation of why plants make good companions. That’s why in this article, we focus on pairings that have been backed by scientific studies, or at least solid common sense. As it is such a vast topic, we’ll also stay focused on three popular plants: the tomato, the genus brassica, and the potato. So let’s dig in.
Photo credit: @insta.greener
Companion planting for tomatoes
Here are the best companions for your tomatoes:
Studies found that planting basil near tomatoes decreases the amount of white flies, thrips, and hornworms that attack tomatoes. This is due to the aromatic oils that basil produces, the smell of which repels the pests. We wonder if it’s a coincidence that tomato and basil taste so good together…there must be some major good neighbor vibes going on.
This pairing is an example of a form and function companion planting. Tomatoes prefer full sun and lots of heat while carrots prefer slightly cooler soil. By planting them near each other, tomatoes provide some shade for the carrots while the carrots greens hold moisture in the soil and slow the growth of weeds. They also take similar amounts of time to grow, so you can harvest them at the same time.
A chemical that is in asparagus can kill nematodes that are harmful to tomatoes. A substance (solanine) that is in tomatoes kills the asparagus beetle which harms asparagus. While not all companion planting is a win for both plants (sometimes one is sacrificed to a pest), it is pretty great when it is mutually beneficial.
Photo credit: Farmer’s Weekly
Companion planting for potatoes
Let’s look at what makes great companion planting for potatoes:
Wildflowers and cilantro
Planting plots of wildflowers nearby has been found to benefit potatoes. The wildflowers attract beneficial insects like ladybirds, lacewings, and hoverflies. These predatory insects eat aphids and the colorado potato bug, two major potato pests. These insects do not cause any harm to your plants, making them an awesome companion planting for potatoes. Along these same lines, cilantro has been shown to attract beneficial predatory insects for the potato.
Potatoes require a good amount of nitrogen to reach their full potential. This often means nitrogen needs to be added to the soil, which can be costly for you and harmful to the soil. Legumes are one of the few groups of plants that are able to convert nitrogen in the air into usable nitrogen in the soil. This fixed nitrogen is then also available for nearby plants. Beans in particular have been found to increase potato yield.
Another form and function companion planting for potatoes. Brassicas have shallow roots and won’t compete with the deeper growing potatoes. I don’t know about you, but I’m already envisioning a grouping of hearty potatoes and broccoli, with beans watching over and wildflowers and cilantro all around.
Photo credit: Companion Planting and Insect Pest Control, Parker et al. 2012
Companion planting for Brassicas
Below are the best companion planting for your broccoli, cabbage, kale, cauliflower, brussel sprouts, etc
Sage, rosemary, thyme, mint and nasturtium
One very informative paper/book chapter lists studies showing that these aromatic plants deter pests from brassicas. Just as basil deters pests from tomatoes, the smell of these herbs and flowers in particular make multiple brassica pests turn the other way.
Studies found that marigolds disrupt the ability for the cabbage root fly to find its target. The cabbage root fly produces maggots that enjoy the roots of all brassicas. Since they attack the roots, you may not notice them until it’s too late. Planting marigolds right along with your brassicas may prevent the fly from finding your plant, therefore preventing the maggots from being born (sorry maggot babies, we don’t want you).
Interestingly, the study showed it was not the smell of marigolds that kept the fly at bay. Instead, marigolds “disrupted the fly’s normal chain of host plant selecting behaviors.” The researchers recorded flies landing and staying for a long time on marigold leaves, staying very still. It sounds like poor Mr. cabbage fly simply got confused about where he was supposed to be.
Herbs aren’t the only ones who can deter unwanted insects with their aroma. The smell of onions also repels brassica-loving pests. So if you’re not much of an herb person, mix in a few onions. Or even better, plant them all and see if any pests are bold enough to make it to your brassica.
Beautiful biodiversity is at the base of companion planting
In general, planting herbs and flowers among your vegetables is agreed upon as a good idea for repelling pests and attracting pollinators. This idea that it is beneficial to grow an array of plants is becoming more and more ingrained in the gardening world. Put in other words, biodiversity is essential to a healthy garden.
A monoculture, growing one plant only, is the opposite of a biodiverse garden. It is a word that brings to mind expansive, never ending cornfields. But the word doesn’t apply to only huge fields of vegetables. When there is only one veggie growing in an area, even if it is your balcony garden, once a pest or disease finds it, it is too easy.
So when thinking about companion planting (even if a companion plant doesn’t directly repel the pest through its smell) the pest will prefer to target an area that has more of its favorite food. If it wants a tomato plant, but all of this other stuff is blocking its path, it may continue on until it finds a bigger and easier to reach buffet.
On the flip side, a more diverse range of pollinators will be attracted by a biodiverse garden, meaning your plants are more likely to be pollinated. Predatory insects that eat pests are also attracted to a range of plants, especially plants that are native to where you live.
So while the specific pairings of companion plantings are useful, keep in mind that diversity is queen. Just like in a forest, more biodiversity means a healthier ecosystem. Lastly, a garden with a lot of textures, colors, and shapes is just so much more visually appealing that a monotone monoculture. All hail beautiful biodiversity.
It is great that some companions have been studied so that we know they really work. As previously mentioned, if you begin to read more, you will find that much of the information out there is not backed by science. That does not mean there is no truth to companion planting, it just means it hasn’t been studied yet. Some gardeners also share contradicting information about what works well together. Even when there is contradicting information, that doesn’t mean someone is wrong. The conditions in each garden are unique, as are the specifics of the vegetables, herbs, flowers, insects, diseases, etc. in each garden. All of these variables affect the way things grow and can lead gardeners to different results.
So if you’re looking for good companion planting for tomatoes, potatoes or any other vegetable in your garden, it is up to each gardener to become the observer, the note-taker, the one who slows down enough to really understand their particular garden ecosystem. We hope with this article we have given you a starting point to take this role. To be the one who understands what grows well together in your garden by tuning in, slowing down, and listening to what your plants have to tell you.
Have questions? Let us know in the comments. And check out our journal at https://thegreenconspiracy.com. Inside, we include four pages of a companion planting chart, providing more ideas for who to plant next to who. Happy spring everyone!
Companion planting for Tomatoes and basil:
- Synergistic Effects of Agronet Covers and Companion Cropping on Reducing Whitefly Infestation and Improving Yield of Open Field-Grown Tomatoes
- Companion Planting and Insect Pest Control
Companion planting for Tomatoes and carrot:
Companion planting for Tomatoes and asparagus:
- Book: Carrots Love Tomatoes, by Louise Riotte
About companion planting for Brassicas and herbs/nasturtium:
Information about companion planting for Brassicas and Marigold:
- Companion planting – do aromatic plants disrupt host‐plant finding by the cabbage root fly and the onion fly more effectively than non‐aromatic plants?
Companion planting for Brassicas and onion:
- Effects of integrating companion cropping and nitrogen application on the performance and infestation of collards by Brevicoryne brassicae
- How to Grow Onions: Onion Companion Planting Guide
Companion planting for Potato and wildflowers:
- Alternatives to Synthetic Insecticides in the Control of the Colorado Potato Beetle (Leptinotarsa decemlineata Say) and Their Environmental Benefits
- High effectiveness of tailored flower strips in reducing pests and crop plant damage
Companion planting for Potato and legumes:
- Nitrogen and phosphorous uptake by potato (Solanum tuberosum L.) and their use efficiency under potato-legume intercropping systems
- Companion Planting & Botanical Pesticides: Concepts & Resources
Companion planting for Potato and marigolds: