How do I make a link that pre-fills a form checkbox?

How do I make a link that pre-fills a form checkbox?

Hi and thanks in advance...
I have a page called contact.htm with a working form. One of the checkbox
fields on the form is named Garden (so either it is checked or not when
using the form).
I have another page that I want to link to my form page, so that if a user
clicks a particular link, they are sent to the form page and the field
Garden is pre-clicked.
I have not been able to do this though I have tried several methods...such
as:
a href="contact.htm?checkbox=Garden,on"
or
a href="contact.htm?checkbox=Garden,checked"
or
a href="contact.htm?input type="checkbox" name="Garden" value="checked"
and some others.
I would appreciate any help.