There is enough protein. That’s not a problem.
Of course, you have to choose the right plants because celery is mostly water, but spinach has a fair amount of protein.
https://www.healthline.com/health/food-nutrition/19-high-protein-vegetables#3.-Pinto-beans
Spinach isn’t as good as it might seem. Bioavailability of the protein is a little over 50% and as little as 2% of iron from spinach is actually absorbed. Doesn’t do you much good to eat what cannot be absorbed.