The picture here is from a few years ago, but this is a yearly favorite of my kids at home. At school we don't really have a spot for this because there's already a nice garden. At home it moves year to year, always going to the spot where we think nothing else will grow.
So, what you've got here are three V-shaped trellises turned upside down and tied together making a 4-sided shape, roughly a tetrahedron, with one side open. We also hang yarn or string (something that will decompose eventually) horizontally around the structure so the bean plants have something to climb on. I don't bother with the careful preparation of the ground (gardeners, put down your scary-looking shovels for this blasphemy). I just dig a trench in front of the trellis, add some lose dirt, plant the beans, and water. The year this picture was taken we put cardboard underneath the tipi because whatever was growing there before gave my daughter a rash. It made it a nice place to hideout.
As for what to grow, choose any bean that will climb. I'm not a gardener and I couldn't find any seeds labeled "pole beans," (stop laughing, you gardeners out there) but I found lots of climbers. We like to plant colorful ones. Even though we eat beans at home I can't seem to get anyone interested in eating these beans. The kids love to pick the pods and shell them. They get used as play money, treasure, and whatever else seems like a good idea at the time. Purple beans are the most fun because of the unusual color for a food.
- Thin the bean plants! If you grow too many they will grow into the center of the structure, leaving no room for children. You'll also get pods that rot before they have a chance to make nice, fat, beans.
- Consider a larger structure. This tipi is really only big enough for one or two children at a time. We've used trellises up against the fence for a tunnel before and this year we're going to prop some up against our deck, which is high and has a nice secret space underneath.
- Weed and water, if necessary. While beans grow fast, the weeds seem to grow faster and will choke out the beans quickly if you don't stay on it. This is one time when the kids will weed for you because they want their tipi.
As I said, I'm not a gardener, but somehow this works for me every year. It's nice to have on a hot day and it teaches kids something about gardening without it being a crisis if the beans don't grow the way you want them to. If you are a gardener I'm sure there are lots of very good lessons just waiting to be learned with the tipi, but we mostly just enjoy ours. I'm hoping that having my kids learn to enjoy being with plants will motivate them to learn how to keep my house plants alive. *I* certainly don't know how to do it!
Note: I found two acceptable spellings of this structure, tipi and teepee. I don't know which is the preferred, so feel free to tell me.