You have the option to fulfill your membership dues with a Work Trade in additional to the required 2 hours per month, you will be required to commit to 10 hours for each 75-150 sf plot your have.
E.g. if you have two (2) 150 sf plots and elect to use this option you will need to contribute 20 hours in addition to the 2 hours a month over the course of the season for a total of 32 volunteer hours over the course of the season (May-October).