In English they are called tree nurseries, in German tree schools (Baumschulen).  In this particular one, the little firs are working hard at becoming Christmas trees.  This seems to be the reception class.

And here, the almost A-levels.  Maybe they are ready for next year.

https://ceenphotography.com/2017/01/13/cees-odd-ball-photo-challenge-january-13-2017/