This paper describes a method for generating flower growth animation in which a petal surface and shape can be changed in real time. Most plant modelling currently animates the plant development process by assuming a time interval and the corresponding growth direction, and cannot easily change the time step or deform the shape. In the model presented here we use a graphical representation for plant growth function, along with a new description of plant growth rate, to enable the user to obtain flexible parameters for surface control. The model generates non-deterministic results which give more realistic and varied petals than can be obtained using pre-defined surfaces or interpolating between given initial and final shapes.