We've all been there. Well, here's the problem: You're trying a big experiment when a small experiment, one that's quick and economical, will do the trick. Here's how to do this.
Pick a smaller area where trees and mountain meet, and try a solution just there. Maybe this spot covers only a couple of square inches, but it should be sufficient to test out your idea. Because you're experimenting in a small area, you can quickly try different solutions until you hit on the right one. Then you can carry this solution to the rest of the painting.
Anytime you have large adjacent areas—and it doesn't have to be just two but can be three or more that meet—and want to get the relationship right, try this approach. I use it all the time. In many of my landscapes, for example, I'll find a small spot where tree, mountain and sky meet, and I work out the color and value relationships. Once I've got the right solution, I can very quickly paint the large shapes correctly.
By the way! Just a reminder about my book. Beautiful Landscape Painting Outdoors: Mastering Plein Air is the perfect gift for your beginning painter friends -- and the advanced painter will enjoy it, too. And hey, it would also make a nice gift for yourself! You can get it at Amazon. (While you're waiting for your copy to arrive, you might like to watch the video interviews I made with several of the artists.)
And don't forget my May workshop at Bluebird Studios in Santa Fe. Santa Fe is an awesome place to hold a plein air painting workshop -- great scenery, but also lots of extracurricular activities like galleries and museums! Details here.
Last but not least, my 50% Studio Sale on Southwest paintings continues through December 24th. Check out the artwork here.