For the watering system I think the separate solenoid approach would work best for us. I am thinking of using the DHT11 or DHT22 temperature and humidity sensors with one (or more) inside and outside to be able to make adjustments according to the difference between the sensors. The Vegetronics soil sensor is a good idea and I will probably put one for each watering line so the plants can be watered differently. I am planning on getting classroom kits and using LED's to simulate some of our activities ithe greenhouse but the kits seem to focus on building the circuit boards (bread boards). Would the student need to build their own relay boards for the greenhouse would it be better to purchase these separately. I plan on having and LCD screen in the circuit box to make on aite adjustments, probably using toggle switches but I would like to have a wireless router providing feedack to a classroom computer for students to monitor the greenhouse and make adjustments. Also, we are working on robotics using the C++ language, but I have been told that industrial PLC systems use ladder logic more frequently. Am I hindering my students by focusing too much on C or C++ programming?