I'd be very interested to hear how you grew it from a cutting, sounds like something I may like to try in the future
Truth be told willow trees just need water to root and you can root cuttings as thick as you can find. I was reading a bonsai forum where a guy rooted a fallen branch as big as his arm. He cleaned up the broken potion (clean smooth cut) threw it in a 5g bucket of water and he had a good sized bonsai tree in a very short time. They are extremely mold and rot resistant and have medicinal properties.
I took some cuttings from a local tree, threw them in a Gatorade bottle with water and left them in the sun. When the weather started getting cold in October, I took it and put it in my sump. I took an outdoor flood light (38w) and placed it close to the cutting. I leave the light on 24hrs a day. I just looked at it last night and it looks like it has spider mites, so I'm gonna have to remove it in order to treat. They are thirsty trees and extremely fast growing.
If I had better lights and there was a little more nutrients I think it would have exploded. It was free to collect and start so I couldn't beat it. People use Mangrove trees all the time especially in SW applications for nutrient export. They die after a while in freshwater because they can't get some of the micronutrients that are found in the sea water. Willows are typically found on river banks and ponds all freshwater so I figured it was a better option to do the same thing.