River birch roots oozing up water in area where I I want to plant a garden

Asked May 5, 2020, 5:14 PM EDT

Our large 3 trunk river birch was dying so we had it cut down and the stump ground down. Many large roots remain and I don’t think it was ground down far enough. There seems to be a “floor” of wood and roots about 6” down from what was the surrounding grade. It is now a mess of wet clay soil mixed in with wood chips and doesn’t seem to stop. The roots coming into the surrounding area are huge can’t be dug out. I wanted to extend a perennial garden in the area. What can I do to fix or clean up the problem?

Hennepin County Minnesota

3 Responses

You will have to wait about 3 years for the roots to rot. A large tree always has lots of large roots. Compost should be be added to break up the clay. Wait until the area dries out before walking on it or doing anything to avoid compacting the soil. Adding perennials after adding compost should be fine. The design will have to be more naturalized than formal until the roots break down. Pick shallow rooted plants. One thing to consider is what happens after a tree is gone. The break down of wood chips will deplete nitrogen from the soil so I would cover the area with mulch to make it more attractive for this year and plant next year. planting is still an option but the plants may be pale and not grow as well as plants growing in a location without so much microbial activity. This is temporary.

What if I remove all the clay mixed with wood chips and fill with compost? I would add a little native soil. Can I add anything to speed up the wood rotting?

There is a product called "stump out" or stump remover that is cellulase. It is an enzyme that breaks down wood. Mixing in compost or replacing the clay with compost would probably have the same effect. Compost will gradually break down so it will not fill the hole indefinitely.