Great rusty stuff.

As for positive advice: avoid using lichen for bushes. The simple fact is, that it does not look realistic enough. Go out to your garden/ local park and search out some roots, twigs and use weeds, moss, ferns for leaves. You could also buy P.E leaves if you wish.

Info on preservation:

1. The Glycerine method. Glycerine or Glycerol is readily available at the pharmacy of at some supermarkets. Take your plant (moss, fern, leaf etc.) and put it on a piece of tissue paper. In a jar, mix 1 part Glycerine with 10 parts water (1:10 ratio). Put this mixture into a spray bottle and mist your plant. I don't fully understand the scientific jargon, but I believe the Glycerine/water mixture will be absorbed by the plant, the water will evaporate but the glycerine will stay in the plant, preserving it.

2. Pressing. With smaller weeds/leaves, putting them inside a notebook for about a week will sometimes preserve them. Make sure as soon as you take the plant out of the book, you paint it.

Chas