The same thing is happening here, too. I am thinking of removing the purple trailing lantana from the containers and planting them in the ground in the hottest area of my garden.

Our weather is off-and-on very, very hot, then cool and rainy. Strange summer here.

Cameron

I'd cut them back and fertilize them. It was certainly the dark, cool weather that caused the problem, though those purple blooming varieties don't flower nearly as heavily as the others.

Well, after I wrote the earlier comment, mine were blooming today!

It's funny...I've done research on these plants and some sources say watering and fertilizer slows down flower blooms while other sources recommend fertilizer.

I took them out of the containers and planted them in the ground. I was thinking of waiting a few days then trimming them back by 1/3 and giving them some fish emulsion. What do you think?

I happen to be a firm believer in the benefits of cuttings back an under performing plant. If this were mine, it would be lopped by more than a third (2/3), and given a dose of soluble fertilizer, mixed to container recommendations.

But that's me. The conservative route is what you are comfortable with and you are certain to have a good response. My way would probably be faster, though.