Becky, the reason you were taken to the home page is because you were signed in and the site recognized you. If a non-member or someone who is not signed in uses your link they will see this page.
If you look at the link you will see your screen name is part of the code, that is how Dave will no that you sent them. If they decide to come back later, it will depend on how they return to the site. If they just type in allthingsplants.com, then you will not get credit, but if they bookmark it on their first visit, then they are bookmarking you link and you will still get credit.