NEW YORK -- For months the growers have listened carefully to the agricultural advice of the Cornell Cooperative Extension agents. Now, it is harvest time at one of New York City's most-advanced farms: the hydroponic rooftop garden of the High School for Environmental Studies on West 56th Street.

The harvest will take place on Wednesday, Aug. 20, from 8 until 9:30 a.m., at the High School for Environmental Studies, 444 W. 56th St., near 9th and 10th Avenues in Manhattan. You are welcome to cover the harvest and the selling of the produce at the market. For information, contact Jackie Davis-Manigaulte, Cornell Cooperative Extension, (212) 340-2945.

On their summer vacation these students learned to grow crops hydroponically -- without soil -- on their school's rooftop, as part of the Cornell Cooperative Extension-New York City program "Hydroponics Learning Model." A dozen city youths learned to grow leafy vegetables, which they will sell at the Union Square Farmers' Market at 14th Street and Broadway, between 10 a.m. and noon.

Hydroponics is the process of growing plants in a nutrient solution (without soil). A hydroponics unit is constructed by using plastic pipes, wood, fluorescent lamps, aquarium tanks and simple tools. The program uses the Nutrient Drip Flow Technique (NDFT) to feed plants and vegetables, and the vegetation grows at a rate five- to ten-times faster than using the traditional "in the soil" method.