When you do your drawing, don't draw the beach grass, or weeds. You will put them in at the end. You can draw them in then, or freehand them, which is what I did.
Wet the sky down to the horizon, and put in some diluted yellow ochre. If you don't have yellow ochre, you can use yellow, but the yellow ochre is softer and won't turn green when you add the blue clouds. Be sure to do the next part - the pink and the blue clouds while it is still wet.
While the sky is still wet, add some diluted alizarin crimson, or whatever you have that will make pink, and then quickly add some ultramarine blue clouds. I missed a little alizarin crimson in with the blue to make them more purply.
Mix a very pale puddle of burnt sienna and ultramarine blue to make a blue-ish gray for the sand. It's okay if there are a few streaks.
Paint the distant land mass with ultramarine blue and a bit of alizarin to make it a purply blue. Add some of this color where the water meets the wet sand. Use any left over paint from the sand color to make some shadows in the sand.
Now you can either sketch in the beach grass with pencil, or freehand it. Use yellow ochre for the first layer.
Add some grass/weeds in burnt sienna.
And finish it off with some really dark weeds/grass using burnt sienna and ultramarine blue. You can add in some weeds with watercolor pencils if you want.