here is the Demo about how i do foilage that has been asked for. I hope it is helpful for somebody.
I took a lot of photos and tried to put them together so you could see every step. This is in no way a refined work, only a demo to show you the process, for a finished piece one would have to work more carefull to fill up specks and so on but you know that yourself.
The drawing is about 5 x 4 cm in size (pretty small okay but the technique is the same for larger work) Okay here we go.....
a) i put in a rough outline first to decide what the trees and bushes should look like and think about where the light is going to come from
b) with a light green (limepeel in this case) i put in the first layer with a scribbling motion making broken circles and swirling movements (no hatching, would not work with the angles you get from that) I am careful to let some holes in the tree (you know the ones for the birds
) and put in a bit of trunk and branch here and there. The left (our) tree has a fairly light bark so that bits do not show up to much in the small photo.
c) did the same base layer of light color (Chartreuse for that one) on the other tree and put in the branches.
d) further on with the left bush and its lightest color (spring green) as that one would be in the shade of the tree above the lightest color is darker
e) and the lightest color for the last bush (celadon green) to make one with a more greyish green
You can see everything is quite rough now, lots of paper showing through but the outside shapes are pretty much defined now.
f) i felt something was missing on the left and so i put in another bush there (apple green) and i added the baselayer of cloud blue for the sky to define where the holes in the tree are (put blue between the green where i left free space in the first layer of light green)
h) here i start to refine the form, with the light color (limepeel here) i go back in and define where the shadows would fall in this tree (sun is supposed to be left upper corner)
i) you can see the left tree is ready... i took a matching darker green (Marine green as that one is a bit to the dull side) and darkend the shadows a bit. Still i use a broken scribble movement to put them in and a very sharp pencils, trying to avoid straight strokes, every stroke should have a curve. I also darkened the trunk and branches a bit to make them show up.
did the same to the right tree, first going back in with the chartreuse to work out the shadows further, then darken them with applegreen (one could go further on and add maybe olive green to the shadows to make them still darker)
j) you can not see much differnce in this photo but i took a light yellow color (cream for the left, deco yellow for the right) and gone over the lightest parts of the tree where the sun strikes most to highlight a bit there.
k) now downwards to the bushes... mostly the same technique here, broke scribble movements and first defining the shadow areas with another layer of light color, then a matching dark color to darken further.
l) put in an even darker green for the shadows on the bush as it would collect more shadow then the tree would. And again go over the lighter parts with the base color and a yellow.
this is the end... i worked out the last bush with the same technique but with greens on the greyish/blueish side. I did different combinations of greens on each tree to show the possibilies of creating different varieties of trees with differnt color and shape. I could go on and on for another 2 h on this little thingy to make it more refined and looking even more realistic but i feel, that the basics is all i need to explain, about layering and refining and adding detail and again detail you know already. The only thing really important with this technique is not to make straight strokes, keep it all scribbly curved and think about where the light and shadow would fall to define the shape. And most of all .... look at trees outside very closely to see how dark shadows really are in differnt light and how light the highlights.
Hope this helps and if you have any question or would like to try yourself and show to ask questions about your work, just holler... i'll try my best to explain further.
Oh and if you want to see what it looks like when it is all refined and worked out look here : http://www.wetcanvas.com/forums/showthread.php?t=356658