Hello, I dont know much about russians but collard greens as well as swiss chard, spinach, parsley, rhubarb, beet leaves and carrots are all high in oxalic acid. These things should not be the stable food source. I wouldnt totally avoid them or anything else. A better choice for torts not on hay would be dandelion and spring mix without the spinach(my costco has one) as well as a very varied assortment of other veggies and some mazuri soaked and mixed in.