OK, This sounds fun!
so according to Wikipedia there are
Big Five personality traits:
openness to experience (inventive/curious vs. consistent/cautious): so that might mean you are more or less happy with experimenting with different plants and growing styles.
conscientiousness (efficient/organized vs.extravagant/careless): whether you like organised or chaotic gardening
extraversion (outgoing/energetic vs. solitary/reserved): gardening alone or with friends/as a team
agreeableness (friendly/compassionate vs. critical/judgmental): not sure about this? how likely you are to want to share your produce and plants or grow the biggest cucumber?
neuroticism (sensitive/nervous vs. resilient/confident): this is a bit similar to openness, but more to do with fear and calmness so how likely you are to panic over spots on your rose leaves perhaps.
This doesn't take into account other constraints such as time and space for gardening. I'm certainly one for biting off more than I can chew. Luckily I'm a laid back non competitive gardener, so I can live with a bit of chaos!