I garden because it's the only form of therapy I can afford.
I don't garden for food, although this year, I am going to try growing some "Bright Lights" Kale, some red Romaine Lettuce, and a salad mix--I bought those to provide a seasonal cover for an area where I have bulbs planted, and we might as well eat them if they grow. Also just bought some strawberries and a blackberry plant for containers.
I garden primarily to provide myself with a sanctuary. Several years ago, when my job was very stressfull, I'd go outside in the mornings with a cup of coffee for myself and a soft pad for my heart dog, and we'd sit on the front porch and watch the flowers grow. When pain and exhaustion from Fibromyalgia get me down, I sit outside on warm days, between the herb garden and the Woodland Garden, just outside the back door. I listen to the bees humming on the Rosemary, I can smell its resiny scent, and the warm sunlight eases the aching muscles and joints. On cold or rainy days, I sit in the armchair by the front window, and watch the birdbath under the Japanese Maple. Birds seem to prefer that one, probably because the Maple provides a dense cover for it. Planning the garden gives me hope, something to look forward to, when I feel better: Yes, I'll move that flower here, this flower there, remove that shrub, prune this, stake that, and I want these new perennials and shrubs, and where shall I put them???
I garden for wildlife. My garden isn't yet the wildlife sanctuary I want, but it's getting there, slowly. I have food, shelter and water . . . and I'm gradually adding more plants, removing those with little wildlife value and replacing them with others that have higher value.
Mostly, I garden for me. When my garden pleases me, I can see how it cheers up people who walk by--I can see them turn to see the flowers, and they smile. Human beings need gardens, need flowers, need trees. I believe without green, growing and blossoming things, our bodies may survive, but our souls will shrivel and die.