I think an interesting question would be why are metaphors used? Metaphors are usually used to desribe something that can't be described in a practical or scientific way, or transcends the barriers of words. I read something a Tibetan lama wrote awhile ao but it stuck with me. He asked how it was possible to understand a language of a higher consiousness with a mind that had not reached that consiousness. He also said that our language could never describe higher consiousness because it is a byproduct of our regular consiousness. This is why all spiritual traditions are steeped in metaphors, they describe things that could not be described in any other way. Also they make us think of things that we know well in a different way and this adds to our depth of understanding. I think the easiest metaphor a garden can be used for is spiritual growth. I covered this pretty extensively in my individual presentation, so I will keep this breif. To grow we need to be nutured with the proper substances and energies. Much like a fragile plant, we must watch our growth to maintain it because we are suceptable to many diseases of body, mind, and soul. Our true inner beauty unfolds like a flower blooming. The metaphor could go on infinitely. Other things it could be used as a metaphor for is anything that grows or develops over time. Even something as mundane as a business could be likened to a garden. This also needs to be nutured and continously cared for.