A community garden project should be kept simple as possible, whether large or small. Bylaws are rules which govern the internal affairs of an organization. They are required when you form a non-profit corporation, but are useful even if your group is a club or a group of neighbors. Many battles are won simply because one side has more pieces of paper to wave than the other. It's helpful to look over bylaws from other similar organizations if you are incorporating.
Flexibility is important when goals and members change.
The purpose, goals and philosophy of the organization. Membership categories and eligibility requirements. Membership dues, how much and when paid. State what officers are necessary, how they are chosen, length of term, their duties and how vacancies are filled. State special committees, their purpose and how they operate.