landscaper
designs everything in an “area” (such as a yard). It may involve reshaping the ground, introducing water features, borders, mulches, and perhaps rocks. Plants are often included in this as well. The good news is that you don’t have to be an expert in gardening. If you want repeat business, it helps to know which plants will thrive in a particular environment, but you don’t need to be an expert.

Horticulturists
are coming from the other direction. Since they must have plant expertise, they cross into the land of the botanist quite a bit, but their field is the garden itself. For a good reason, horticulturists often talk more about soil than plants, as the ground is, of course, a significant factor in gardening. Besides considering sun exposure, water requirements, drainage, and pest susceptibility, horticulturists often do a lot of landscaping since gardening crosses into that area.