This is a really useful system of planting a variety of plants together, for the benefit of one or more of those plants. A well known example of this approach is the “Three Sisters” used by indigenous people of Central and North America. The three plants are Maize, Squash and Beans. The Maize provides support for the beans to grow, the Beans provide nitrogen from the air, via their root nodules and the Squash shades the soil, retaining water and reducing weeds.
There are many beneficial relationships between plants, as described above, but there are also plants which have detrimental effects on certain neighbouring plants (Allelopathic) by releasing chemicals through their roots when alive, or during decomposition so it’s useful to check for these to (see links below).
Companion planting can be used in several ways to help the “target crop”. A screening crop can stop pests from seeing the target crop whereas haven plants nearby can support predators and pollinators. An aromatic crop can reduce pests’ ability to detect the target crop, for example interplanting carrots and onions where the onion smell is said to mask the smell of carrots from the carrot root fly and the carrot plants can deter onion flies. A popular trap crop, such as Nasturtium is used to keep pests away from the target crop. Pests are attracted to the trap crop, rather than the target crop. The beans in the three sisters, and legumes in general, provide nitrogen which they fix from the air, in root nodules formed from a symbiotic relationship with bacteria.
I have discovered a type of companion planting in my own garden when I got frustrated with ants “farming” aphids (yes, the do that!) on my Globe Artichokes, taking them to the sweetest, softest parts of the plant (the flowers I wanted to eat) so that they could harvest the sweet, euphemistically called “honeydew” or aphid poop! After looking for a way of persuading ants to move elsewhere, rather than killing them when they tried to invade my kitchen, I found that spraying the entry points and skirting boards of my kitchen with water and peppermint essential oil, the ants moved on. So, I planted mint around the base of the Globe Artichoke plant and, touch wood, the ants have stayed away!!
When I first discovered companion planting in the 70’s as a curious teenager, I had to rely on a couple of books, whereas now, with the Internet at my fingertips, I can find this information I need much more easily. One of my “go to” sites for companion planting information is a Wikipedia page: https://en.wikipedia.org/wiki/List_of_companion_plants I know that Wikipedia is generally not accepted as an academic source of information, but as a guide, it is very helpful. I also came across a free, printable companion planting chart here: https://www.smilinggardener.com/organic-vegetable-gardening/companion-planting-chart/
I’ve printed it out at A3 and it works really well at that size. Of course you can always download it and look at it on your pc, rather than printing it.
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