David there is a wealth of info on greenhouse maintenance on our Greenhouses forum here on ATP.
http://garden.org/forums/view/...
Since I live in Florida I really don't need one, but I do run an outdoor school garden at our local elementary school. Our growing season here runs concurrent with the school year, so we grow edibles from September through April. We have both food crops and a butterfly garden since we needed to attract pollinators to the new garden area (formerly part of the playing field).
I can tell you for sure, all the kids get much more kick out of growing something they can eat. When you show them a potato and say "what's this?" they all know but when you turn the potato around and show them where it is sprouting and say "then what's THIS?" they are absolutely captured by the idea that the potato tuber they would normally eat is making a new baby plant that will grow many more potatoes. Then, after the plant has grown, you should see the excitement when they get to dig up potatoes! It's a treasure hunt, especially of you grow gold, red and purple potatoes.
Every aspect is a learning opportunity, even a dead or dying plant, a bug or caterpillar eating a leaf "What can we do about this?" "Why can't we let the cute little bug live on our plant?" We talk about non-toxic solutions to bugs and disease - hand picking caterpillars (you must have the kids wear gloves, then they will touch everything) and just removing diseased leaves to spraying benign things like soapy water and baking soda solution to prevent the bugs/fungi but not poison the food.
We talk about everything from photosynthesis "the leaves are nature's solar collectors" "the sun on the leaves makes food for the plant" to re-nourishing the soil, composting, soil testing and really scientific stuff for the older kids. We teach Kindergarten (age 5) up to 5th grade (age 12). I tried a garden at a middle school (6th to 8th grade) a few years ago, but the kids are much more into interacting with each other at that age and it was not as successful.
