Avid gardeners like ourselves have sometimes been stumped by the conflicting information you’ll get from different gardening pros and horticulturists. Sometimes they’ll even contradict themselves. Or worse, you’ll set up a companion planting scheme and discover that the insect repellent properties of, e.g. garlic to repel red spider mites from tomatoes, was completely ineffective in your particular garden habitat.
So we created a survey of plant companions from four sources to ascertain which combinations they generally agree/disagree on, with the understanding that observing and documenting our own results is really what matters in the end … though may not always apply every season!
Click here for PDF version of summary tables. © 2009 Plangarden
A PDF of the tables appears on the right. More details are in the slideshow below this post.
Here are some useful terms often used in the context of CP: allelopathy and phytotoxins. Allelopathy (allelo- “one another”, and -pathy “disease or suffering” from Greek) refers to how plants find ways to stake out their territory, often by harming nearby neighbors. They may release phytotoxins (phyto- meaning “pertaining to plants”) which essentially attempt to knock out nearby competitors. Phytotoxins can sometimes also repel insects and other animals.
Some notoriously allelopathic plants harmful to the vegetable garden (though may be great at deterring pests which we’ll discuss in Part IV) are the eucalyptus, black walnut, and absinthe wormwood. Make sure you know what lies just outside your property line if you decide to grow vegetables in that area.
Limited research has gone into subsoil fungal activity and its respective role in companion plants. Some speculate that both beneficial and harmful compounds may be transmitted through the mycelial network – though it’s impossible for everyday gardeners to ascertain “fungal contributions” to the companion plant ecosystem.
In the end, what we suggest is to “not get overwhelmed” on which combination of plants will produce the ideal garden. Our “strategies” post offers a starting point in figuring out what to grow. Perhaps the initial approach in using these tables would be to scan those combinations least likely to yield beneficial results (the red circles), and then move on to the good companion pairings.
Is owning a book on companion planting an absolute must for the gardener? Personally, we feel that you can get sufficient information to jot down notes from library books or from the Web. However, if you love to experiment and collect gardening books, then look through the book reviews on Amazon.
In our next post, we’ll cover companion planting as it relates to the contribution of flowers, herbs, and insects to your overall vegetable garden.
Good guide. I found that planting antique roses with my tomatoes turned out to be a good combination. Who knew.
As for the wormwood, when I started gardening in the 70s, we would make a wormwood tea to deal with pests. I always used it lightly with the thought that it may be bad for me if I harvested a vegetable with a large dose of the tea on it.
Hi Frank, thanks for your post. Yes, apparently tomatoes do a good job in protecting roses against black spot, thanks to an alkaloid called ’solanine’, once used as an insecticide (see CP, Pt II, Ref. 2). Nightshade plants, while being susceptible to various pests and diseases, can also be pretty good in fighting them for other plants.
Wormwood’s a strong natural insecticide (great to have as outer borders of your property) but growth inhibiting to other plants. We’ve read of people planting them in weedy areas, but prune them back regularly as wormwood can take over an area quickly.
[...] you through knowing your plant families to some common blunders. Followed up by a comparison of companion planting guides, all in handy pdf or snazzy slideshows. It’s great stuff, a handy reference with plenty of [...]
Very interesting. My garden is going gangbusters especially the tomatoes. But the only thing not doing well is the bell pepper….which is planted in the same bed next to fennel and strawberries. Chart says this is bad combo and seems to be the case for my garden.
Hi Marcy,
Riotte suggests to plant fennel away from the veggies (esp. tomatoes) as it’s one of the least friendly neighbors. And if your recall, bell peppers and tomatoes belong to the same family (nightshade). However, its small flowers seem to attract beneficial insects, so perhaps it’s best as a border plant and/or in containers.
[...] instance, sunflowers may be great weed deterrants as they were found to be strongly allelopathic to weeds like wild mustard, jimsonweed and ragweed (Ref 1, p. 310). Or what about selecting a [...]