Tough love doesn't work for everyone. If he is healthy, you can withhold for 2 weeks. I've only had one case of a dragon who didn't eat any greens at all. She is a pet that I adopted last year at 3 years old from someone who housed her with a group of girls, and she just assumed that she was eating her salad. I keep all my girls (pets, breeders, every single dragon) separate. And when I put her in her own home, I realized that she just wouldn't even touch them. All the tough love in the world didn't work for her. Clean fecal, perfectly healthy, no reason not to eat greens, especially a fully grown adult whose diet should be 80% greens. Then in the winter, she brumated, woke up in February, and has been eating her greens every day ever since. Not really sure what my point is, except not to give up. Sometimes, they will fix themselves. But always offer and maybe something will change. I personally don't think there is anything wrong with eating just collards. Variety is ideal, but at least he is eating SOME greens, and that is better than nothing.