I’d like to talk about the Three Sisters. No, not the play written by Russian playwright Anton Chekhov, and not the three mountain peaks near Canmore, Alberta , Canada. I am talking about Three Sisters Agriculture used by Native Americans; corn, beans and squash.
If you have read anything about companion planting you will have come across a description of the Three Sisters as one of the best examples of companion planting that works. But have you ever seen any data to show that this system works? Did the Native Americans actually use this system?
The Three Sisters are the corner stone of the companion planting movement and if it is all a myth, is there any validity to the whole idea?
Companion Planting – The Three Sisters
What is it? Seems like a simple question, but as you read this post you will realize that it is not as clear cut as you might think.
This system is normally presented in the following way. It is an agricultural practice where corn, beans and squash are grown together. The bean benefits by climbing up the corn. The corn benefits by having the squash shade the ground, preserving moisture and keeping the roots cool. Both the squash and corn get fertilized by the bean which is a legume that fixes nitrogen from the air.
What a beautiful system – if it works. And that is an issue. Everyone talks about it as if it works, but almost no one checks the facts – except for Garden Myths.
Did Native Americans Use Three Sisters Agriculture?
You might think this is not an important question, but it is. You see, many authors use the fact that Native Americans used the system to validate the system. If they used it, it must work. There is of course no logic to this reasoning.
I am no historian, but numerous online reports say that Native Americans did use the Three Sisters. For example, “Jacques Cartier in his voyages up the St. Lawrence in 1534–1535 detailed the cultivation of the Three Sisters in fields near present-day Montreal.” (ref 1)
But things are not as cut and dry as many would lead you to believe.
- Native Americans were not followers of companion planting. Instead they used the system “because it required less time and labor than planting the crops individually.” They did not use it to increase yield.
- The crops were planted in large mounds which significantly affects yield, something most modern day suggestions fail to include.
- Corn production is good as a three plant polyculture, but bean and squash yields are much lower. The three sisters polyculture was used when corn was the main target crop , but it was not used when the main goal was to produce beans or squash. Then the more productive monocultures were used.
Native Americans did use the system, but not because it was a very productive system (more on this below). They used it, some of the time, to make their job easier.
Milpa – Another Form of Three Sisters
The Maya peoples and other Mesoamerican people of Central America used a similar system called Milpa agricuture that produces maize, beans and squash. Crops are grown for 2 years and then the land is left fallow for 8 years to recover.
Which Corn, Beans and Squash Were Used?
We copy the Three Sisters system because it supposedly works, but which type of seed were used by Native Americans?
Most modern day examples of this system suggest that you plant sweet corn, green beans, and squash.
In reality Native Americans grew maize, dried kidney beans and usually pumpkin.
The varieties of plants used by Native Americans was very different from the seeds grown today. Even if the historical companion planting system works, there is no reason to conclude that today’s seeds will also work.
Issues With The Three Sisters
The logic used to explain why the Three Sisters works is flawed.
Beans Produce Nitrogen
It is true that legumes fix nitrogen from the air, but almost none of the fixed nitrogen enters the soil around the bean plant. It is all used by the bean to grow and produce seeds.
When you harvest the beans, especially dry beans, there is very little nitrogen left in the plant. So even if the plant is dug into the soil, it does not add much nitrogen to the soil.
The corn does not get nitrogen from the bean plant next to it.
Squash Reduces Soil Evaporation
This statement is true because the large leaves shade the soil. But you have to remember that the squash and beans also use water from the soil. So they compete with the corn for water. Wouldn’t a wood chip mulch around the corn work better?
Three Sisters and Square Foot Gardening
I found numerous discussions about using the Three Sisters method in square foot gardening and in raised beds. Some of this is nonsense. Imagine growing all three crops in a 4 x4 ft raised bed? Some people are trying to do this.
Others recognize that you need more space and talk about 10 x 10 ft beds or 4 x 12 ft beds. That might be large enough, but consider the fact that the Three Sisters method used mounds of soil. In effect it is a raised bed without the side walls. The side walls of today’s raised bed really don’t provide any benefit in such large beds, except maybe aesthetics.
Does Three Sisters Agriculture Work?
The system obviously works because it has been used for several hundred years, but it is important to define what we mean by “works”. If works is defined as producing a crop, then we can easily conclude it “works”.
However, in order for this to be a good companion planting system it must produce more food as a polyculture, then the individual plants would produce as a monocultures. Growing these crops is all about growing food. If it does not produce more food, then it is not a good companion planting system.
Jane Mt.Pleasant has looked into the food produced by Native Americans using Three Sisters and concludes that, “This polyculture cropping system yielded more food and supported more people per hectare compared to monocultures of the individual crops.” It certainly seemed to work for them, but keep in mind that this conclusion is based on a lot of historical data, some of which is extrapolated which makes it difficult to reach firm conclusions.
There is limited scientific testing of the Three Sisters system in modern agriculture. One study that compared growing just corn to corn plus southern peas, showed an increase in yield when the two crops were grown together.
A feasability study to see if corn monocultures can be converted to Three Sisters polycultures in the Midwestern United States concluded that it would produce less yield, mostly due to the type of soil in this region. This research used mathematical modeling and not actual plantings.
A Master of Science Thesis tried growing the crops in Wisconsin, in two different areas. The study was only carried out for one year which limits its value. It used heirloom varieties, rather than modern day hybrids. This study concluded that:
- There was no difference in yield per plant between monoculture and polyculture.
- Calories per acre were greater in Three Sisters treatment than in monoculture for one of the sites, but not for the second site.
What does all this mean. From the limited amount of scientific studies we really can’t reach any firm conclusion. It is possible that the Three Sisters perform better than monocultures in some situations, but probably not in all situations. There seems to be no study looking at modern day hybrids so we don’t know if they work. The fact that it was used historically does not provide evidence that the Three Sister polyculture outperforms monocultures.
The current scientific evidence is not very strong to support the use of the Three Sisters. There is certainly no evidence, that I have found, that supports using it as the poster child for companion planting.
If you do use this method, it is important to use the hill method, which is quite different than the way most people arrange their crops. Details for this can be found in reference 1.
Just For Fun
You might be interested in Three Sisters, other than the one discussed here.
- Developing an Effective Southernpea and Sweet corn Intercrop system; http://horttech.ashspublications.org/content/3/2/178.short
- Feasibility of Converting a Corn Monoculture into a Three Sisters Polyculture: https://sites.tufts.edu/gis/files/2017/06/Polakoski_Grace_CEE187_2016.pdf
- An Evaluation of the Productivity of the Native American Three Sisters’ Agriculture system in Northern Wisconsin; https://epapers.uwsp.edu/thesis/2007/Martinez.pdf
- Image source for square foot gardening; https://kbsgarden.wordpress.com/three-sisters-square-foot-garden/