In this photo taken on Saturday, Feb. 9, 2013, instructor Ted Smith uses a slide to demonstrate different types of damage to marijuana plants during class at THC University in the Tivol

 

              In this photo taken on Saturday, Feb. 9, 2013, instructor Ted Smith uses a slide to demonstrate different types of damage to marijuana plants during class at THC University in the Tivol
In this photo taken on Saturday, Feb. 9, 2013, instructor Ted Smith uses a slide to demonstrate different types of damage to marijuana plants during class at THC University in the Tivoli in Denver. Chemical fertilizers can be finely crafted to target a specific deficiency in the plants, whether they’re lacking phosphorus, evident by telltale “purple vein,” or potassium, a likely culprit when leaves show brown spots between the veins. (AP Photo/Ed Andrieski)