Are the sickly ones all together or scattered throughout? Has anything been sprayed in the area (including by neighbors) that could have drifted to them? Are they close to thirsty trees or other shrubs that could have taken water and nutrients away? What do the leaves look like besides yellowing... any spots, "dirt" on them, signs of spiderweb like stuff? Can you post pictures?

Answers to these will help but the best way to get a diagnosis is to take samples to your local cooperative extension office and let them look at them. Don't spray or otherwise treat them until you know for sure what's going on.

Good luck. I love my Encores.

Sandy

I have encore also. I had about 8 at my inground pool. They were in full sun. They looked awful. They would not bloom, they looked like they were about to die. The nursery where I got them at said get them out of the full sun. So I dug them up and planted them in part sun/ part shade. They are so much better now. She also told me to sprinkle some Hollytone around them and they bloomed.It was to hot for them in full sun. CeeCee