Well before you go and try to do something new you should fix your site.
1. Your site Harvest.com is not https ! SSL is free. Make the switch. It is costing you rankings in the serps. I am curious why live.harvest.com is https while harvest.com is not..
2. Never use sub domains unless it really makes sense. You lose PR ( page rank ) when you use sub domains instead of sub folders. Suffice to say you would benefit more from using sub folders.
3. Cross domain linking is something that can be hazardous to your site. Even if it's a sub domain linking to the parent domain. Especially if it's in the menu area and sitewide. ( This little issue would go away if you used sub folders btw.)