How much does your garden grow? A lot, if your garden is the New York Botanical Garden and you measure growth in the number of greenbacks invested in the world-class horticultural institution. Over the past 15 years, the garden has put $600 million toward repairs and improvements, scientific research, exhibitions, and an endowment. That fact was noted by the garden's president, Gregory Long, and chairman, WIlson Nolen, last night at the garden's Conservatory Ball. And the ball made its own humble contribution: with 600 guests, the event raised $2 million. [photos here]