Good Morning, 

Thank you for contacting the U of M Extension Service. 

Based on your question, you want to start a flower garden at the base of a dead tree stump. 

You can surely add soil and/or compost to the area to install a garden. You will probably be fighting the roots of the tree, if you are digging in the soil.  If you don't dig out the roots, you could add enough soil to the top so it would not be necessary. 

it will take several years for the roots to decay. You might consider doing a soil test to see what you might need to add. As the roots decay, the soil may need additional nitrogen. 

Here is a link to the U of M Extension Yard and Garden website: https://extension.umn.edu/managing-soil-and-nutrients/soil-testing-lawns-and-gardens

Good Luck!

Kristi, 

You cut off the tree, so the stump is dying. The stump may appear alive as you cut down the tree last summer? It will eventually dry out and the stump and roots will die. This may take awhile, but the stump is dead. 

Again, if you are digging in the soil around the stump to install your garden, you may have to chop through or dig out some roots. As I said before, since the tree stump is dead, you could add enough soil on top to avoid having to dig up the roots. But it may be several inches of soil. 

Good Luck!