To subscribe to The Gardeners Exchange calendar using iCal, use this URL:
In Apple Mail, choose File | New Calendar Subscription, then paste the above URL into the Calendar URL field and press the Subscribe button. Name it whatever you like then press OK to save it (change the other settings if you need to first).
In Google Calendar, click the little down arrow next to “Other Calendars” on the lower left of the screen then choose “Add by URL” and paste the above URL into the URL field and press Add Calendar. Generally you won’t want to check the “Make the calendar publicly accessible box”. It is better to refer people to this page and have them subscribe to the source so they get reliable updates when we change the calendar.