nutrients at walmart----no bueno!
as for the greenhouses, they are pimp. i used a couple of them to produce mushies.....lol i fucking love those lil' boomers.
you can mod. it and hook a humidifier up to it for propagation, you can do the same modification and hook up two fans. you can cut out the shelfs, leaving just the rectangle frame of the shelves for support, and then place the unit over a perfect size tub (they have ones the green house frame and plastic part) fit over perfectly, and proceed with an enviromently controlled aero grow, all you need is to mod it with fans and put a radiator heater a foot or two away for temps and humidity.
and if your good like that, you can get two, produce mushrooms in one, run a fan with ducting between the two, pushing co2 laden mushroom air into the pot greenhouse through a hepa, and poof, fuck the tanks and the yeist. i measured the co2 levels in mine without fae and got 1200ppm+
and if your really crazy you can push your fresh o2 from your pot back into the shroom house. cuz o2 is to mushrooms what co2 is to pot. but that could just raise some complications, if one is not too experienced
.........this has been done before. thats all ill say on that.
here is a link to the shroomery version of the greenhouse and a site that will teach you all you need to know to grow those little boomin friends
http://www.shroomery.org/forums/showflat.php/Number/6783616/fpart/all/vc/1
plus check out the computer controlled system he made diy to control temps, and humidity. siiiiick
peace
the brain