Currently I am responsible for teaching horticulture to special needs children in a special school, and part of my task is to advise non-specialists who teach it as one element in their teaching load. One of them recently came to me with a request for ideas for his year 8 class. Something interesting, perhaps. I suggested a three sisters bed.
Native American women used to garden while their menfolk hunted, and they early on discovered the merits of companion planting. This is opposed to the system in which each bed is a monoculture that is rotated round over the years. You plant more than one species of vegetable in the bed, putting together plants that can support each other in some way. This is a method becoming more popular with the organic movement and with Permaculturalists, who prefer to grow plants together rather than in discrete beds.
The Native American women grew beans of various kinds, but they knew that bean stalks needed supporting, so they grew them alongside maize, which we know as sweetcorn, so that the strong maize stems would support the beans. However, women dislike weeding as much as men do. and they knew that between the tall stems weeds would spring up, so they planted pumpkins as low growing ground cover. Their broad size and wide-spread leaves shaded out the weeds. This is an example of companion planting in which the plants are in symbiosis.
To make it effective you neeed to space the seeds out, and it may be a good idea to propagate in pots. Leave enough space for the pumpkins [squash will suffice just as well. It is a good idea to give the pumpkins a start ahead of the taller plants, as their young seedlings might otherwise be shaded out. The beans should go in slightly after the maize has developed. This is because maize, especially in colder climates, requires a longer time to grow, and so that the beans will have something to support them. Remember that beans cannot stand frost, so plant only after the last frosts are over, which in Britain should be May at the earliest.
It is advisable to plant maize in blocks, rather than rows, as this aids pollination. This is because maize is wind pollinated, as you can tell from its small flower, so in a block it has a better chance of spreading polen around than in a row, where the pollen of the plants at the end of the row is just blown away. In Britian gardeners often shield maize[ sweetcorn] to protect it from winds, and they do this with fabric screens.
This kind of bed, however, is greedy for food, so it takes much manure and compost to get a decent crop. Be unsparing with the applicaton of these important substances. Before you plant apply them as abse dressing, and during planting be ready to apply fertiliser on a regular basis. Remember, pumpkins can grow huge and so need masses of food and much water.