You cannot delete your account.
Ask them to do it manually using this form: http://davesgarden.com/helpdesk/home/
In your message, include the email address you used for signing up.
Please note that AccountKiller.com is not associated with the business listed on this page. AccountKiller provides easy-to-understand instructions and guides on how to cancel charges and relationships from the list of businesses on our site, we have no affiliation with these businesses.