Dimitri's in Harlem, the Chelsea Garden Center, several farmers at the Greenmarket, and the Matterhorn Nursey in Spring Valley (just north of Westchester). I would have to say my favorite is the Chelsea Garden Center, for its selection and accessiblity. Pitch: "This is my second summer with a space to garden! I have a very sunny, west facing balcony in Woodside Queens. It is "L" shaped, wrapping around a fire escape. The largest part of the "L" is 4 by 13 feet, along the railing. The other part of the "L" is 4 x 6 and crowded; it's where the practical 'human' tools live: a table & 4 chairs, work bench, hose and grill..." [more below]
I grow a lot of different things on my balcony, and it's easiest to sort them by their purpose. Herbs: thyme, lavender, orange mint, parsley, chives, sorrel, basil, bay, and rosemary. Greens for my uromastyx lizards: escarole, curly endive, mizuna, bok choi, red dandelion. Fruit: meyer lemon Non-edibles: roses, nigella, chinese lantern, morning glory, amarylis, pitcher plant, juncus spirales, ivy, sedum, blue fescue grass and about five other flowering & foliage plants I can't remember the names of. Often my houseplants make spend sunny days on my balcony; these include an avocado tree, a string of hearts, and a variety of cacti & succulents. Everything is doing well, despite exposure to a lot of dust generated by ongoing brick work on my building. I have attached three pictures of my balcony garden. One 'general' shot that captures most of my plants. One detail of my 'bog' planter, with the pitcher plant & the juncus. The last has my rose, but it's mostly the view over my railing, it was a little hazy this morning, but you can just make out the Citibank, Empire State & Chrysler buildings.