the same fertilizer and watering times?
 

This is my first year teaching agriculture and I am trying to get some hydroponics going. My greenhouse is set up this way: I have feeder tubes for taking up the fertilizer directly into the water flow; I have lines that run across the greenhouse the spray spickets coming out of the main lines; I have a furnace and fans running on both ends. My questions are as follows: Can I grow tomatoes and watermelons on the same watering line with the same fertilizer and watering times? For my fertilizer I mixed Grow More (hydroponic) 4-18-38 (NPK) (8 ounces), 4 ounces of calcium nitrate, and 4 ounces of magnesium sulfate in 100 gallons. This was the recommendation on the sack for seediness Does it sound right?

The solution is being sprayed on through the spickets. How often should I leave these on and how often?

I am transplanting them from a soil mix into perlite for the hydroponic substrate. How big do the plants need to be before transplanting?

We tried to do some in class but I believe the watermelons damped off (looked like they had been pinched at the medium level) and the tomatoes leaves wilted, turned a brown color, and died. Any suggestions would be helpful.
My name is Mike T Tesnohlidek and I teach ag. science in Nyssa, Oregon. Thanks

Yes that sounds right for a standard commercial hydroponic mix and can be used for a variety of vegetables.

You didn't say if your water returns to a reusable reservoir but from your description I don't think so. So watering cycles are tricky with a non retrievable system. You want to try and water only what the plants consumes so all your nutrient solution doesn't run out the bottom to wherever. Disney World does this by weighing 1 plant in each row measuring how much water the plant consumes thus letting the system water all the plants in that row the same.
I would which your garden to a reusable system if possible unless you have deep pockets.

Let them get well rooted before washing the dirt off and they will have a better chance for survival.