No, for the time being Plottie breeding can only occur with 1 or 2 parent plants, but no more. The only way for a Plottie to be made out of 3 Plants or more is through the use of a Frankenpotion.
Frankenpotions allow you to combine up to 4 Plants to create a Plottie. However, these potions are in very limited supply and can only be purchased during flash-sales and pop-up stores around October-November.