As an ACGA member, you can sign in with your email address and member ID number. There is a "Retrieve password" button that will email you your member id if you need it. You will need to know what email address you used when you joined ACGA. If you aren't sure what address you used, you can email firstname.lastname@example.org to inquire. Or, if you did not provide an email address and would like to, you can also email email@example.com to add your email address.
If you are not yet a member, now is a great time to join! Go to http://communitygarden.org/support-us/become-a-member/join-the-acga.php to join ACGA.