I'm a grass guy and now wish to get my plantings in order. I had a landscaping company come and install the front beds and I have moved and added some plants to the back. In a precious thread my hydrangeas were yellowing and drooping. I applied some osmocote per my father in laws suggestion(he's a flower and plant loving guy). They have perked up now but still a little yellow and he suggested applying jacks water soluble Fert every 2 weeks or so. The Fert I have is a general purpose 20-20-20. I am going to apply some to the hydrangeas at 1 scoop per plant. I'm curious if it is ok to apply some to the other plants in my landscape .... Knock outs, black eye Susan's, lillys, rhodos, gardenias, etc.