Can't see tree's or grass unless i'm very close.

It has do with the setting under Tree and Detail objects. The settings are tree distance and detail distance setting them small will only show them near you.

I've had weird things happen with tree or grass meshes, even some that I have purchased. Some of them appeared to be extremely small.

When you are in the details tab (the one with the flower), and you add a new detail, are you adding a grass texture (as a 2d plane that "stands up"), or are you adding a mesh?

Try it as a texture, and see if you see anything. Also...you did select the new detail afterwards, and paint it onto the terrain right?

If that doesn't work, try posting a screenshot of your details tab, and also double-click on the detail and show us the settings you have for your detail.

To add to an old post if someone has the same issue. Unity does something strange every now and again in the project in which I can't see anything unless medium close up. I can't see an entire terrain mesh. Maybe I'm missing something about how it displays but I have searched all over the program and found nothing that helps. Changing the layouts does nothing however after opening an old project which displays correctly, save the current layout with a new name then open your latest project again then select the new named layout and everything displays as it did before.

I think that what you're looking for is the "detail distance" property from the terrain settings.