Other forms: horticulturalists
A horticulturalist is a knowledgable and experienced gardener. If you work growing vegetables, flowers, or other plants, you're a horticulturalist.
Horticulturalists work in the field of horticulture, a word that's derived from the Latin hortus, or "garden." The word horticulturalist, which is a variation on horticulturist, is generally used for someone who gardens professionally, at a botanical garden or a plant nursery. But if your grandma is an expert at plant propagation and soil pH, you can definitely call her a horticulturalist.