thx guys!
the base was quite simple,
first main shape with styrofoam and metal foil (the one you use when cooking), secondly covered that with paper towels dipped in future (sidolux in poland) after that I mixed some sand with wood glue aplied that, mixed some more, diluted it with water aplaied. and then painting - first gray primer from a can then various shades of grey using 'el cheapo acrylics, painted with brush and drybrushed after that sprayed some hairspray and added leaves from used teabags - BIG thx to terrainoob for that tip/technique.
I'd say that the base is quite simple IMO...