I have a 50-year old magnolia tree at the front of my house that I love and don't want to risk doing anything that might harm it.

Most of the area under the tree is bare ground, and I was wondering if I could plant a ground cover like ajuga that might grow there and eventually fill in the bare ground, but without doing any damage to the tree or its roots. Is it safe to try?

It is perfectly safe to plant some ajuga under it. Just try and dig in between the main roots so you minimize any damage that may/may not occur. Then to keep it happy, keep it watered.

Thanks. I'm just waiting now for all of the blooms to fall off so I can rake up the solid carpet of petals I now have covering the front lawn :D. Then I'll plant the bugleweed being very careful to keep holes small and avoid any roots. As fast as it spreads, I don't think I'll have to plant many to get it to start covering the bare ground.

Thanks again.