You would just need some appropriate foliage since plain clump foliage might not look right.
On that subject, I find that flock glued on top of clump (foam) foliage looks quite good, as long as one puts a little effort into first arranging the clump foliage into natural shapes. The clump foliage provides depth and an appropriately "billowing" look, while the flock adds the actual "leafy" surface texture. You can leave the undersides and the crevices of the clump foliage unflocked, if you like.
Noch makes a flock-like product called "leaf flake" which is especially good for this and many other plant-modelling techniques (it may not be available everywhere but I really do recommend tracking it down for anyone who's serious about terrain modelling in the larger scales), although I like to alternate between the various flock varieties I've collected for different trees, bushes, shrubs and thickets, so as to achieve a more varied (if perhaps somewhat naive) look. All that being said, I do also use "naked" clump foliage as a leafy/"needly" texture in the larger scales.