This is the cultivation of plants as part of horticulture
It is a more specialized version of agriculture, right?
Yes It is ornamental plants are often grown for their flowers, foliage, or overall appearance; 
What kinds of plants are we talking about?
We are talking about gardening :) useful plants, such as root vegetables, leaf vegetables, fruits, and herbs, are grown for consumption
Do people have to go to school to work in this field?
No, it's mostly a hobby and a relaxing activity
How long have you been interested in this hobby?