As we hit the middle of February, some of us green thumbs (and aspiring green pinkies!) start looking forward to warmer greener months and what we might like to grow. Maybe we are looking for a visual feast and are picking out our flower varieties. Some of us are looking for a more traditional feast of some home-grown veg. I personally like growing a combination of the two… which is part of what we will be talking about today.

I know I have mentioned companion planting in the past (most recently in our last sustainability article that you can find HERE) and I am pretty sure that Mikaela has brought it up a couple of times as well. Obviously, it is on our minds a LOT and for good reason. There are a lot of other innovative and fantastic methods for growing amazing gardens and crops that I want to talk about soon. Just like I love mixing and matching what we grow, I love mixing and matching and even hybridizing different techniques to match the situation and need. For now, though… let’s focus on just one thing.

Strap in because this may become one of my longest articles (I love planning gardens, food forests etc!). So, let’s look at what it is, some of the pros and cons (both scientific and ethical), some mistakes to avoid, and some good and bad companions.

A Quick-ish Definition

Companion Planting: Noun: The close planting of different plants that enhance each other’s growth or protect each other from pests.

– Oxford Dictionary

So, I could just leave you with the Oxford definition but the reason this is a “Quick-ish” definition is that I wish to add a bit more before we move on. I won’t go into what it can do since that will be covered in our pros, but I do want to clarify this definition more. Companion plant is a form of polyculture (versus monoculture crops where there are fields of just one crop). I also want to point out that companion planting should be for a MUTUAL benefit of both plants or COMMENSAL (beneficial for one and neutral to the other) … otherwise you are just looking at a parasite and a host which doesn’t even sound nice in this context.

Pros: Why We LOVE Companion Planting

I am going to TRY (key word- try) to keep my bullet points brief because this could easily become a novel (actually there ARE books on it). I will try to do this in the other sections as well. Also, I am really going to try sticking with more commonly held beliefs and facts that I can back with science. I will get more into my preferences and my own planning in a future post.

Increased Yields

I am putting this first as it is the biggest recurring benefit in every book, blog, and article I have seen thus far on the subject. The HOW of this varies by the combinations and honestly this is a product of a combination of most of the other points on this list.

Maximizing Space

One of the more obvious ways this maximizes space is that planting different species in the same area means you have to spread out less. Another thing to consider though is that we live in a world that is not flat. I am not going to get into the whole flat world debate right now. What I mean by this is that there is a Y axis peeps! Or for the less mathematically inclined…. There is an up and down, multiple layers, you can build up, OR further under the ground etc. Trellises aren’t a new concept, but you can really expand on this concept in other ways.

Soil Health

Plants have evolved their root systems in different ways; shapes, secretions, and uses vary widely and affect the soil differently. The concept of crop rotation (also a technique I endorse) is partially built around this knowledge. Companion plant allows you to take advantage of this on a micro scale. For example, planting legumes like beans, peas, or clover will help nitrogen to the soil and are an attractive option to plant with Nitrogen greedy plants. Root veggies like carrots or radishes displace soil as they grow and will help prevent it from getting compacted.

Repelling/Attracting Pests

I realize that putting repelling AND attracting pests seems counter intuitive so please hear me out. Certain plants release chemicals and oils that are unattractive to pests. It doesn’t poison them or block them… it just makes the habitat less attractive. An example would be Marigolds (especially French marigold, Tagetes patula– Bonus points that this is an edible variety) releasing Alpha-terthienyl from their roots that helps inhibit the development of some nematode eggs such as the root-knot nematode (Meloidogyne spp.). Additionally, a lot of aromatic herbs contain compounds such as estragole, linalool, eugenol, etc. which is unappealing to taste/smell for many (not all) pests. Just remember that some of those plants need to be around for at least a year to see the results (like the Marigolds). On the flip side, knowing how to use your pest attractants is also useful! For example, I sometimes see Nasturtiums (pretty and edible) listed for managing pests is companion planting. They help but not how some beginners think and can be a negative if used incorrectly. Aphids LOOOOVE them. They are what we call a trap crop/plant and are used as a more attractive host plant, so the Aphids are less likely to bother your more valuable crops.

Attract Beneficial Predators

Not all insects are bad. Ladybugs, Lacewings, Preying Mantids, Hover Flies, Predatory Beetles, Syrphid Flies. The list of good ones is looooong and if you are gardening you are going to have to come to grips with the fact that THERE WILL BE BUGS. So why not try to make a good home for the ones you want? Some plants to attract the good guys are Dill, Anise Hyssop, Blooming Cilantro, Mint, Chamomile, and Bee Balm are known for other reasons (edible, pollinator attractant, etc.) but they are also catnip to a lot of insect predators because of leaf cover, fragrant blossoms, and sometimes even the nectar in a few omnivorous cases. The point is though that many of these predators will help control your pest population. Aphids, Mites, Thrips, Squash Bugs, Cucumber Beetles, Tomato Horn Worms, and Cut Worms better watch their… back? Thorax? Segment?

Attract Pollinators

The last bullet point transitions nicely into POLLINATORS! This is a really hot topic for a lot of people with the whole save the bee movement. Planting attractive plants for a variety of pollinators as companions will help maximize your yield. We do want to attract bees to help propagate our plants but let me throw this thought at you…. We aren’t necessarily primarily looking for that classic black and yellow bee the newbs are thinking of.  Expand your consideration to more native bee species, aculeate wasps, some fly species, ants, butterflies, moths, beetles, bats, and even some birds (hummingbirds duh). Depending on where you live, this list may vary a bit and definitely depending on the plant, some of these pollinators are more relevant.

Repelling Weeds

I will be transparent on this one that I know less science on this point. I do see it is a pro for companion planting if accurate and if this is proven incorrect, I am not losing anything by planting more plants. What I have read is that some plants release chemicals from their roots that can be toxic to weeds. I was having trouble finding the real science to back many of these claims. The most substantiated claim I found was that of Sunflowers since they can release Heliotropin, sesquiterpene lactones, and phenolic acids… the problem is that they can also be harmful to some plants you want as well (the exception being the three sister’s combo we will talk about later). A more useful application, in my opinion, if used correctly is that of ground cover companions in between crops, that block out and outcompete their weed companions.

Provide Shade

Companion planting with taller, more sun hardy plants can offer needed shade in areas where it is lacking. I am from Arizona and often ran into issues with TOO MUCH SUN! It can be just as damaging as not enough.

Living Trellis’

I mentioned before when talking about maximized space, that this style of planting allows you to also maximize your vertical space. This is a bit more specific though. Some plants grow strong upright and others need something to use as a trellis. You can just buy one at the Home Depot or the Tractor Depot… OR you can companion plant. For example, Corn and pole beans work as a fantastic team with the pole beans growing up the stalk of the corn.

Aesthetic

A pro of this type of planting can honestly also just be aesthetic since it often means staggered flowers and fruits for an extended period, so I feel you get a longer period of enjoyment out of your garden.

Saving Time

Don’t you think having less pests and weeds to deal with would save you time?

Polyculture:

This is something we have spoken about in a couple different articles and contexts. We are big on polyculture instead of monoculture farming on an industry level. So why wouldn’t we count this as a pro and support it on a smaller, more local level. You can even take this a step further and turn it all into a food forest (I swear I will be talking about all these other techniques and garden layout styles SOON).

Increased Biodiversity

Companion planting allows you to have more plant biodiversity which will, by extension, attract and support more wildlife biodiversity.

Cons: Things to Consider

I struggled a bit on listing true negatives to companion planting. I can’t find anything particularly damaging or harmful about it (if done correctly) over any other garden planning style. Instead, my list was more like things to consider before jumping in with both feet. Cautionary words maybe?

You may also notice the list is a lot smaller. I have been openly biased more heavily on the PRO side of companion planting, so I decided to play devils advocate and try digging into this a bit more actively. It was still a struggle still struggled. I few other blogs touched on things briefly and will mostly likely have a similar list. There wasn’t much in the way of conclusive studies though (which I will get to) no matter what university or professional journal I turned to. That said, let’s look at what I was able to come up with.

Takes Time to Plan

I actually enjoy this and can sit around for hours planning for hypothetical gardens I may never see. For some though, this may be a drawback. It takes research, planning, knowing your environment/soil/climate, and a clear idea of what your final goal is.

Not All of It Is Supported Scientifically

As I mentioned above… there are not many studies to back a lot of companion planting info out there up. I tried to (and will continue to) use examples that have some more backing. I have a science background, so it makes sense to vet info and if you are telling me to do something, I want to know the how and why. A lack of scientific study doesn’t mean it is all hogwash though. Many of the claims of why certain plants go together have been passed down through the years for a reason. But also because of that you have to consider how the info may have been warped through the years or how it may have varied results in different gardens or climates… which leads into my next point.

Environmental Variables

Temperature, soil moisture, soil pH, sunlight, and nutrient availability all affect plant growth, are variable for each plant, and are constantly changing. Some species are not adapted to live in the same places which might limit things depending on where you are. Also, those variables may hinder some plants, effectiveness.

Not A Cure All

Remember when I mentioned French Marigolds ability to help control root-knot nematodes? Notice I said, “help to control” not “cause root-knot nematode genocide”? That is because companion planting is not going to cause you to have no weeds, no pests and auto-unlock the ability to grow squash the size of your cocker spaniel with no blemishes. It is a tool to help in the garden, not the magic eraser of gardening world chaos.

Not All Plants Are Compatible (ie sunflowers)

This is on here because something to consider is that while companion planting can be a positive, if the incorrect plants are together, you may notice one or more of them suffering.

Common Mistakes to Avoid

PROS. Check. CONS. Check? If you are still reading, I am going to assume you are still interested in companion planting. Further down, I will go over some good and bad companions but first, let’s look at some common mistakes and how to avoid them.

Using Trap Plants Incorrectly

Trap plants attract pests to hopefully keep them off other, more prized crops but they can be more detrimental than helpful if not used correctly. I am going to use Nasturtiums as an example since I mentioned them earlier. They attract aphids. But aphids can take over easily and quickly if left unchecked and the population will outgrow your plant and easily spread to others in the area, negating the good intent of companion planting or even making it worse than it would have been. You still need to kill the aphids. You plant your trap plant and when the pests are drawn to it, you treat the concentrated group of pests however you prefer.

Allelopathic Plant Combos

Some plants are what we call allelopathic, meaning they inhibit the growth of another plant or organism due to a chemical release into its surrounding environment. It usually hinders growth or germination. Some of these only affect certain plants or affect most plants and have just a few exceptions.

• Highly allelopathic plants include perennials like black walnut, rhododendron, sumac, and elderberry.
• More mild ones can be found in garden vegetables like mustards, fennel, sunflowers, and buckwheat.

Clumping Crop Families

Try to avoid large clumps of similar plants in the same family. They tend to attract the same pests and it will just compound the issue. The onion family tends to be an exception since they mostly repel pests but some families to think about breaking up are:

• Brassicas: kale, cabbage, cauliflower, broccoli, mustards, radish
• Solanaceae: tomatoes, peppers, eggplant, potatoes
• Cucurbitaceae: cucumbers, melons, zucchini, summer squash, winter squash
• Amaranthaceae/ Chenopodiaceae: chard, beets, spinach, quinoa

Planting Too Close

Think about not only how big your plant starts but how big it will become. If you plant too close, more aggressive growers or larger plants can choke out crops.

Conflicting Maintenance Needs

So, it seems obvious that conflicting needs lead to… conflicts. Duh. But consider the following.

• Water Needs: Some plants need more or less water or drainage. Take this into consideration when picking neighbors. Additionally, remember that plants with deep root systems will “steal” water from veggies and plants with shallower roots like carrots or tomatoes. This can be mitigated to some extent by keeping soil consistently moist, using mulches, and utilizing soaker hoses and/or drip irrigation.
• Soil Needs: This is where it is good to know what type of soil you have and what your plants prefer. Without completely replacing soil, it is difficult to make huge changes to it and even harder to have a huge difference between multiple chunks in close proximity. Plants will be unhappy in the wrong soil textures or pH so do some research before hand to help you decide what to grow.
• Nutrient Competition: some plants need a LOT of nutrients in the soil for growth and then to fruit. Avoid neighbors that are less aggressive like herbs or spinach. You can consider ones that need little nutrients and/or put some back into the soil, like legumes. Additionally, don’t be afraid to add nutrients to the soil if you have poor soil. Composting or slow-release fertilizers are always an option.
• Planting Style: One article I read on “Epic Gardening” had a fantastic example of what to avoid. “[…] Potatoes need to be hilled to keep their tubers underground. If they were planted next to broccoli, cucumbers, or strawberries, those crops could end up buried or suffering from stem rots due to excess soil mounded up at their base. It would also be logistically difficult to get your shovel or hoe into the space to mound up the soil around the potato plants.”

Overshading Companions

While some plant combos benefit from the taller one giving the shorter one partial shade (i.e. Tomatoes and Lettuce), you need to be cognizant of the fact that there is such a thing as too much cover. Plants need to photosynthesize which means that they need light. If you let your smaller plants, be completely overshadowed, they will suffer. You can help avoid this by trellising anything that vines and paying attention to when and where the sun hits your garden to better plan where to put your more (or less) sun greedy residents.

Incorrect Timing

Think about how fast things grow. For example, if you want a plant to be on a live trellis like corn, the corn needs to be established a couple of weeks before you maybe transplant instead of location seed your cucumbers. And some plants aren’t useful at attracting pollinators until they are flowering which takes time.

Wasted Space

This is me talking about trellises again. But honestly! One of the biggest benefits of companion planting is maximizing space so why wouldn’t you trellis if you can? On a slightly different note, this is also about timing because you can think about the fact that while some plants are smaller (before they grow up), there is a lot of unused space in between that you can grow quick crop in and harvest it before it is an issue. For example, while tomatoes are young, you can grow radishes or lettuce and harvest them before the tomatoes start blocking the sun.

Aggressive Growers

Some plants grow VERY fast and will take over. Mint, Clover, Rosemary, Bambee, Thyme, Bee Balm, Blackberries, and Morning Glories, Asparagus and Rhubarb will quickly take over other plants. Stick to having them in their own separate beds, pots, or contained margins.

Forgetting Ground Cover

Don’t forget your ground cover! They help block weeds, keep soil insulated, keep ground fruits off soil, add cover for beneficial predators, sometimes act as a barrier against certain pests, and help conserve water among other things. Side note… a lot of plants great for this role are edible and also useful as a substitute for grass lawns. Creeping thyme, sweet alyssum, and dichondra are favorites of mine for this reason. Mint would be as well but not with veggies, and it will choke them out.

Mixing Annuals and Perennials

Keep annual and perennial beds separate (though they can be near for benefits) otherwise you will have beds with plants that stay year after year and become woody and established that you have to disturb yearly for your annuals. You are just asking for a mess. If you have a perennial plant and are struggling to find a good companion, think Lavender, Sage, Mint, Rosemary, Rudbeckia and other coneflowers, Yarrow, and Daffodils.  

Weird Shaped or Shapeless Gardens

This is totally up to you but there is a reason that farmers grow crops in rows. It makes it easier to weed, see what is going on with crops and gauge spacing needs.

Good and Bad Combos

By this point, I have thrown a lot info at you, but I have not given you a clear-cut list of what plants you should and should not put together. This is because, as mentioned before, this is not always an exact science. What I would recommend is to start with lists like those found in the farmers almanac, free charts you can find online, your local nursery, or the lists down below, but DO NOT TREAT THESE LIKE GOSPEL. Do some research. Know your climate and soil. Experiment. I have a list of sources at the end of the article but my two favorite I personally love to reference when planning are from Cornell University and the Farmer’s Almanac. Also the lists I have next are by no means exhaustive… there are so many more options and combinations and you might find that some work for you and others do not or that you discover something completely different you need to share.

Good Combos:

• The Three Sisters: Pole Beans, Corn, & Winter Squash. It is so popular that it has a name. The winter squash provides ground cover and the corn acts as a trellis for the beans.
• Cabbages and Aromatic Herbs: cabbages are catnip for pests (trust me). Planting aromatic herbs (like basil or rosemary) in the vicinity will help repel some species.
• Cucumbers, Radishes, and…… Sunflowers: The sunflowers will provide some much-needed shade for the other two and can be used as a trellis for the cucumbers if you pick them before they get too big or if you stake your sunflowers up (not a bad idea regardless). I know sunflowers are allelopathic, but they affect some plants (like pole beans and potatoes) much more heavily. This combo should be one of the least affected.
• Tomatoes, Marigolds, & Basil: I read in some places that basil can help improve growth and flavor of your tomatoes. I couldn’t find scientific documentation of this (just a lot of blogs claiming that there is proof). You will have to try for yourself. What I can tell you is that it is said to repel some insects including mosquitos and be a light antifungal. Marigolds we have established can repel some predacious nematodes. You lose nothing by trying this combo and if it is true then you get more, bigger tomatoes.
• Cucumbers and Nightshade plants: To be more specific, if you plant seedlings rather than seeds of nightshade plants such as tomatoes, eggplants, and peppers near cucumbers, they will benefit from less weeds in their area. Cucumbers are actually allelopathic so they will release cinnamic acid into the soil which will stunt germination but if your neighboring nightshades are already germinated, you get around this pesky issue.
• Crimson Clover and Fruit Bushes (like Blueberry): Clover can take over, but fruit bushes are big enough and hardy enough that this is not an issue. The clover is Nitrogen fixing and will also attract pollinators and then sustain them when your fruit bushes are no longer in bloom.
• Lettuce with Sweet Alyssum and Yarrow: Yarrow is a mellow companion and ideal for most combos but can grow a lot/take over like Dill. In combination with Alyssum though they will attract braconid parasitic wasps that will kill aphids and caterpillars that ravage your Lettuce. The Alyssum can go in and around the Lettuce with Yarrow as an edging crop nearby.
• Marigolds and Alliums: Remember me talking about French Marigolds and how they disrupt nematode life cycles (only really noticeable benefits after a year of having the marigolds there)? They also help with Onion Maggot Flies. Both pests are a hazard to your onion, leek, and chive crops.

Bad Combos:

• Tomatoes and Cabbages: I am specifically putting this here because I have read that tomatoes will repel cabbage moths; they are both heavy feeders so they will compete for nutrients. They are also susceptible to some of the same disease and can pass them back and forth.    
• Plants within a singular plant family. For example:
  • Brassicas: kale, cabbage, cauliflower, broccoli, mustards, and radish
  • Solanaceae: tomatoes, peppers, eggplant, and potatoes
  • Cucurbitaceae: cucumbers, melons, zucchini, summer squash, and winter squash
  • Amaranthaceae/ Chenopodiaceae: chard, beets, spinach, and quinoa
• Strawberries and members of the Brassicas (Cabbage) family: Strawberries will hinder the growth of your broccoli, cauliflower, collard greens, etc. Strawberry plants can be attractants for snails and slugs which the cabbages are particularly weak to AND they tend to like more acidic soil than cabbages.
• Strawberries and members the Solanaceae family: Potatoes, Tomatoes, Peppers, and Eggplant are susceptible to the disease Verticillium and can pass it to your strawberries.
• Onions and Beans: They need different growing conditions, and the onions are more forgiving so in the incorrect setting, they will easily outgrow and hinder the growth of your beans.
• Cucumbers and Aromatic Herbs: Sage and other aromatic herbs release oils (not contested by anyone) that are said to either hinder growth or change flavor of cucumbers when grown in close proximity. This is one I would like to test because I question its validity, only because different sites say different things.
• Potatoes and Asparagus: Potatoes and asparagus rhizomes occupy the same space so when digging up the potatoes you would damage the perennial asparagus rhizomes.
• Corn and Tomatoes: They are both nutrient greedy and sun loving. They will constantly compete for both and suffer accordingly.
• Carrots and Dill: These are in the same family and so will attract the same pests; carrot flies, spider mites, and aphids. Additionally, the Dill bolts, while they are a great companion for some plants, they will overshade your carrots and compete for root space.
• Sunflowers and Potatoes: I keep saying it… Sunflowers are allelopathic. Potatoes seem to be one of the plants that affect most.
• Blueberries and Veggies: Blueberries like really acidic soil which is usually out of the veggie comfort range.
• Rhubarb and anything low growing: Rhubarb gets HUGE and will block out sun for your shorties.
• Pole Beans and Beets: Bush Beans and Beets are fantastic together due to compatible size and beans adding extra nutrients like Nitrogen to the soil. If they vine though, they can block out much needed sun so the roots stay small and the leaves turn pale.  

If I missed something (I know I missed lots) that you feel is relevant or want to impart some wisdom on the rest of us, please leave a message below! This is meant to be a community and that means sharing information and learning from each other.

Until next time!

Taylor

Some The Sources I Used & Reference

Benefits of Companion Planting (Julian Selemin, reviewed by Jabeen Begum, MD)
https://www.webmd.com/a-to-z-guides/benefits-of-companion-planting#1-2

Epic Gardening (Logan Hailey ) 15 Companion Planting Mistakes to Avoid This Season https://www.epicgardening.com/companion-planting-mistakes/

Epic Gardening (Logan Hailey ) Companion Planting Gone Wrong: 21 Planting Combinations to Avoid https://www.epicgardening.com/plant-combinations-to-avoid/

Companion Planting (Cornell University Cooperative Extension, Chung County)
https://extension.unl.edu/statewide/lincolnmcpherson/Cornell%20Guide%20to%20Companion%20Planting.pdf  

Is Companion Planting Scientific (Jeff Schalau, Associate Agent, Agriculture & Natural Resources University of Arizona Cooperative Extension, Yavapai County)
https://www.cales.arizona.edu/yavapai/anr/hort/byg/archive/companionplanting.html

The Myth of Companion Plantings (Linda Chalker-Scott, Washington State Extension)
puyallup.wsu.edu/wp-content/uploads/sites/403/2015/03/companion-plantings.pdf

Companion Planting (Robert Beyfuss and Marvin Pritts, Cornell Cooperative Extension)
www.gardening.cornell.edu/factsheets/ecogardening/complant.html

Companion Planting: Basic Concept and Resource (George Kuepper & Mardi Dodson, The National Sustainable Agriculture Information Service)
www.attra.org/attra-pub/complant.html

Better Together: The New Science of “Companion Planting” [Cynthia Nations, Maggie Mah, The University of California Division of Agriculture and Natural Resources (UC ANR)] https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=53468

What is Companion Planting? (Amber Kanuckel, The Farmers Almanac)
https://www.farmersalmanac.com/companion-planting-guide

The Ultimate Companion Planting Guide + Chart (Daniel Sjöberg, founder and CEO of Walden Labs, a certified permaculture designer) https://waldenlabs.com/the-ultimate-companion-planting-guide-chart/#casestudy