Thomas Greene Park, 3rd Avenue and Degraw Street. Help care for and beautify the park by pulling weeds, spreading mulch and planting bulbs. Advance registration is encouraged but not required: bit.ly/TGPHalloween. Hosted by Friends of Thomas Greene Park, Gowanus Canal Conservancy, VOCAL-NY, St. Lydia’s and Fifth Avenue Committee; sponsored by Domain Companies. Ends 12:00 PM.