Wikipedia
A Greensman or Greensperson or Greenskeeper is any production personnel on a film set which is responsible for obtaining and taking care of anything "green" – plants, grass, trees, flowers, and other various landscaping materials like rocks, gravel, sand, etc. Considered part of the art department.
This includes artificial forms of these materials up to and including those representing greens, such as camouflage netting.
Greens work is generally considered to be one of the dirtiest, most thankless, and physically demanding jobs in set construction. In addition to set construction greensmen often work "on set" assisting the camera and other departments in adjusting the set to the changing demands of different camera positions and lighting setups.
Ideally the greensman functions as a participant in the filmmaking process as an extension of the art department during set construction and in conjunction with the camera department during filming. The range of duties in this category ranges from tending to plant nursery operations (watering, fertilizing, transplanting, etc.) through to the artful crafting of vines, trees, flowers and the like using cut living material and various forms of artificial material.
Usage examples of "greensman".
The manse was now grown as decrepit as its final resident, who lived alone except for a single house servant and a greensman whose sole duty was to keep open a tunnel through what had once been a garden but was now long since given over to vegetative rampage.
Linscott, who had, unbeknownst to the other faculty, been carrying on a torrid affair with Mister Taupin, the greensman, had been coming to call on the man who was her secret shame when she had discovered the trio of youths bullying Malcolm Reed near the fountain.
After Centaine had chivvied the coloured greensman, and with Blaine's expert advice, the turf on the field was green and velvety, the going beneath it neither hard enough to jar the legs of the ponies nor soft enough to slow them down.