Bean or Bean Plant.
Apparently I have to explain it...
"Stalk" as in Bean Stalk. Nursery as in plant nursery.
Human Being is usually pronounced Human Bean. (Using mispronounced or misspelled works is acceptable in riddles, so there!)
Pinto Horse, Pinto Bean.
Jelly Bean. (See Note below.)
Kidney Pie, Kidney Bean.
So you see, it all makes sense.
* Note: Instead of the line saying Horse, Jelly, Pie. I think it should have said Horse, Sandwhich, Pie. This would keep the format of puting the type of bean first (pinto) then the second word it is associated with second (horse.) By just putting "jelly," there is no other word associated with it. It should have been Jelly Sandwich, Jelly Bean. Oh welll.