Sometimes, writing is the hardest thing in the world. You have to think twice about every word, struggle with each line, repeat the dialogue out loud before you change it all around. But sometimes, it's not. Sometimes, you'll settle into a groove. You'll get into a zone. And that's when words just start flowing. When that happens, you've got to go with it.
Words Before Agony
I'm a big advocate of doing the research and getting it right, and I don't care what you're writing about. If you're going to describe a tree, I think you should get out your reference materials (like Google) and learn about that damn tree. But I also believe that when the words are flowing, you need to go ahead and flow with them. Because when the well is dry, you'll have plenty of time to do your research.