Planetary influences help us order and conceptualize the world differently from the way we usually do. Certainly when working with plants, we notice that particular properties and characteristics tend to occur in sets that do not coincide with the compartmentalized box that contemporary Western science enjoys imposing on the universe. Perceiving plants from the perspective of their planetary influence can show us relationships between plants and their uses that we would otherwise miss. Plants have great knowledge to share with us, if only we will open ourselves to them and experience them as subjects rather than as objects.
Using the planetary system to learn about plants is one way to begin that process. You can also use the planets as a handy way to order spiritual influences present in various plants. I've compiled plant attributes from various approaches, putting together a portrait of plant characterstics for each planet and element. Using this info, you will not have to rely on books that do not (and probably can't) explain why they identify a plant with Mars or Saturn. You will be able to see for yourself what the influence is.