I posted on this landlord site because I ran across it by chance and thought it would be interesting to get landlords' perspectives on what happened.
The only supplementary information I have is that someone "high up" (according to the super) in the management company saw the collection of plants and pots and made a snap decision that they should be thrown out. No question was raised by this person as to who owned the plants and pots. The area in question is the common back yard of a 12-story building. For several years, a few tenants have put flowering plants in that area. The management agent specifically assigned to the building has been aware of this activity and has complimented some tenants for doing this. But this guy was not the one to have the plants tossed.
I am not aware if any new tenant (who probably pays much more rent, since it is partially a rent-stabilized building) complained about the appearance of the area, which only reflected the chilly April we have had in New York City. In another two weeks, many of the plants in question would have flowered, as they have done for the past years.
In the range of the world's problems, this is certainly not a big one, so I am not going to contact the landlord. In fact, it saves me a few hundred dollars on what I would have spent to keep the area looking good once the hot weather actually arrived.
Thanks to all for your responses. I had no idea the debate would be so spirited!