Here are some quick reasons:
1. It saves you, over time, lots of money. The saved money can be used to pay up mortgage quickly or take an early retirement.
2. It creates a sense of community and fosters friendship.
3. It helps the environment, reduces one's carbon foot-print, helps in recycling as many of the plastic containers, bags, shoes, sheets and other household items that were going to be thrown away in land-fills can be used in variety of ways in gardens.
4. It fosters health as gardening is a good exercise, and one get to eat fresh organic food picked right out of garden. An obesity epidemic is spreading across the world. As per the above video, an average American household spends only 31 minutes every day to cook food, eat and then wash away the dishes!! It is impossible to do all those in 31 minutes, and thus proves that the food are not cooked but brought store-made. Having an edible garden will force one to cook. Cooking is not only creative, but it also makes one move around (and thus have some exercise) and become healthy through eating healthy cooked home-made food. Thus, gardening and cooking also fosters strong family relation as more and more family members start participating.
The above picture is taken from the above-mentioned video. It shows the history of gastronomy
5. Hunger is on the rise and more than 900 million people are hungry in the world. If each of us start growing some of our food, then we will have much better appreciation for food. Food will not be wasted. Thus, all those extra food can go into feeding hungry people.
6. World food prices are rising. Ten years back we could buy so much food with $20 that it would have nourished us for at least two or three weeks. Nowadays,with $20 we can hardly buy much good food. The exotic foods like Jerusalem artichokes, globe artichokes, asparagus, winter and summer squashes, rutabagas, turnips, radishes and beet are not easily available and they are expensive. However, Jerusalem Artichokes, globe artichokes and asparagus are perennial and can be grown even in frigid snowy winters. Chives is another perennial. Leeks, onions and garlic are very easy to grow. Rutabagas, turnips, radishes, parsnips, carrots and beet can be grown throughout the year, even in snowy winters, under some fleece protection. So, again the solution to rising food cost is producing one's own food as much as possible.
7. 10 calories of fossil fuel energy is needed to produce only 1 calorie of food in any industrialized food system. Globally we have reached the peak oil production. So, how will we produce food when the oil sources are depleted? That depletion is happening at a much faster rate as the world population is increasing, our need on fossil fuel is increasing. At the same time, urban population is rising; more people are moving away from farming and rural communities and thus dependence on food produced using fossil fuel is rising. As per the video, the world needs to produce more food in the next 50 years than it has produced in the last 10,000 years combined.
There are many other reasons like sense of accomplishments or help in reducing depressions but the above are enough to start growing even a small patch of edible garden.