I have planted Zinnias in the same flower bed for the past 4 years. The first year they were huge, and plentiful. The second year there were fewer of them but still plentiful. By the third year there was a 2 foot section where no Zinnias came up at all, Last year the section where none grew was more like 3 feet and this year out of the whole 6 foot flower bed only about 6 plants are coming up. This leaves me to wonder if the plants from the previous years have been sucking all of the minerals out of the ground. I do feed them with MIracle Gro periodically and always have.