How does her garden grow? From fertile dirt with rusty nails, beer, and bacteria. At least according to the Exploratorium in San Francisco. Now that spring has arrived, green thumbs are itching to get out and get planting, and this hands-on science museum in California has put together a Web site for experienced and budding gardeners alike. Watch, for instance, as one farmer reveals the secrets of compost and neighbors transform a median strip into a lush garden full of edible plants.