Action potentials are multi-functional signals in plants. While most plant cells are conductive, and electrically coupled with each other, the action potentials are channelled faster along the plants' vascular network. Conductivity of the networks is geometrically constrained, thus allow for selective propagation and interaction between the impulses. Using FitzhHugh-Nagumo model we show that it is possible to realise a functionally complete set of Boolean functions by selecting locations of stimulating and recording electrodes. The results pave theoretical grounds for further experimental studies of plant-based computing.