I would approach it as a compartmental modeling problem.
Plants grow at a specific rate, however some will die (for whatever reason), so this becomes a system of differential equations expressing the overall growth. Also, at some point they reach the limits of thier nutrients (consider electrolytes such as sodium, potassium, calcium, magnesiun) and nitrogen (as nitrates), as well as available liquid water.
They have their predators, such as bacteria, fungi, insects and other animals.
Each of these is a different differential equation interacting with the other variables, together in a system of differential equations, that expresses the overall plant growth. I’m certain you can find information in the literature, and perhaps relevant models, that express all these and that you can use as a basis for your simulation. Much depends on how detailed you want to get.
It might also be interesting to include the plants’ evolutionary strategies, such as creating alkaloids that at least make them taste horrible or in the extreme disable or kill the predators, or become woody or unappetizing in other ways.
Obviously, you can take this to any level of detail you want!