I was kind of wondering about the salt buildup, but I've heard so many people rave about this stuff I really wanted to give it a try. The other thing I took into consideration was that for 6-7 months out of the year I water with rain water which should help with any concerns about salts. When the plants are outside, I also change my watering technique. Instead of spraying, they get water poured through the pot. If we have a warm summer, this will probably happen every day.