How does gardening help the environment?

Gardening does not necessarily help the environment. Lawns in desert climates like the Southwest United States use up precious water resources, and cause a great deal of pollution due to the nitrogen fertilizers applied, and the gas and electricity used to mow and edge the lawns.

Growing natives, or plants that are acclimated to your area will on the other hand protect species where they belong, and encourage local ecosystems. Growing vegetables and fruits helps to reduce the need for produce to be shipped in from far away.

It's a complex question, with no right answer.