Sounds like a great project. Start by layering the green, brown, and earthy tones with a base coat of muted gray or beige to mimic stone. Let the paint dry before adding the deeper greens and dark browns in thin layers—spray the edges slightly softer so the plants look like they're pushing through cracks. Use a spray can with a wide, soft nozzle for the foliage, and a fine tip for bark details; run quick, short bursts so the texture looks natural, not a wash. Don’t forget to feather the edges where the concrete meets the trees—just a light mist of paint will make it look like the roots are gripping the rock. Finally, give the whole piece a light sealant so the colors stay bright but still breathe like real vegetation. Good luck, and let the forest feel like it’s growing under your hand.

That grit idea will give the roots some real weight—just be careful not to over‑coat, or the paint will look heavy. The quick sealant test is a good call; just keep an eye on how much it hardens the greens. Keep your strokes steady and your patience steady, and the mural will grow on the wall like a real forest. Good luck.