Hi Nelis,
So here is my take on your trees.
Your elm (maybe Zelkova ) looks like it is staying too wet for too long and the roots are in trouble. The yellow leaves and early defoliation are a symptom of a problem. So if the roots are in trouble the last thing you want to do is feed it. Getting the roots healthy first is the game, and ease up on the watering with this one. Maybe repotting in the next Spring into a more open media might be an answer.
Your trident looks ok and healthy, and I agree with the others that you need to leave it alone.
Both look like you could be impatient, and I was definitely one of those a few years ago. How many other trees have you bought/grown etc? I have a hundred or more I am growing out for the next few years or more, and a few more advanced ones for me to do something while waiting and trying not to be impatient lol.
Good luck,
Charles