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I first heard of the Maize, Squash and Bean poly-culture method of planting whilst at University studying for my degree in Nutrition and Food Science. It was a method of planting used across the Southern New World most notably the ancient Mayan's used in Mexico have been using this method for around the last 700 years. The Spanish explorer Francisco Vazquez de Coronado even found evidence of this matrix in what is now North America, near Tuscon Arizona. On an early expedition to the San Pedro River valley he noted, “These village-dwellers subsisted on maize, squash, beans, wild plants and animals”.
The three plants together are often called the three sisters. The basic principle behind planting these three plants together is quite simple, the Maize supplies support for the beans, the squash helps to suppress weeds by providing a ground cover (a bit like a living mulch) and the beans fix nitrogen into the soil. Once the corn matures the squashes should be close to reaching maturity and the corn can be harvested allowing the squash to take over the plot. This method of planting is an excellent way to grow a number of different crops in a small space. It does work best in tropical countries but the method can be put into place in a UK or any other temperate climate.
I am in the process of establishing this method of planting this year after a reasonable success with it a couple of years ago. The main draw-backs with the method in a non-tropical country is that the beans will grow a lot quicker than the maize. This year I will supply additional support to the beans with some poles and once the corn is established re-train the beans to grow up the corn instead of the poles. The same method can be achieved with a slight variation of the planting regime with sunflowers instead of corn. You may end up with slightly smaller yields than if you planted each crop individually as they are sharing the soil and of course nutrients with two other plants. However the overall yield for all three would be greater than a mono-crop in a similar sized area. It is therefore ideal for the urban gardener with a very limited amount of growing space. The three plants together can also look quite attractive and could act as a decorative border within a garden as well as a good source of food.