Adding a google calendar to a gardens site

stupidly easy,
create a calendar that you want to share publicly,
right click on the calendar and select settings,
copy the iframe info from the embed this calendar tab.

<iframe src="https://www.google.com/calendar/embed?
height=400&wkst=1&bgcolor=%23FFFFFF&src=hsb5mshe4seh0dbail2ua7pdsg%40group.calendar.google.com&
color=%232F6309&ctz=America%2FNew_York" style=" border-width:0 " width="600" height="400" frameborder="0" scrolling="no"> 
</iframe>

done!