I was finally able to locate all the ingredients for making gritty mix, so today I made my first batch! One of the plants I repotted was a Christmas cactus that spent the winter in an awful peat mixture that was hard and water repellent. I tried to wash it off of the roots, but some of it was on so tightly, I felt like I might damage the roots if I didn't leave some of it on. Will a little of the old soil hurt anything, or is it necessary to have a "clean" root system to benefit from gritty mix?