Organic materials in concrete do not work very long due to chemicals and moisture.
I have seen many organics used in international concrete construction (India, SE Asia, Central America)and they were only posts used to support previously poured slabs on multi-story buildings and removed before they sprouted (usually a week or so to avoid and expansion forces). They never even considered anything but light reinforcement steel in concrete that was available and usable for the long term structure life.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.