Beginner Gardening: tree roots, 1 by Yellowbricks

Yellowbricks wrote:
We have a 20 year old magnolia that was found as a volunteer sapling with three leaves and now is 25-30 feet tall and growing. It's roots extend into the bordering plant areas for which I have always made allowances with watering and fertilizing. However as the roots approach our house foundation, I am thinking about trimming some of these roots. I've read two conflicting opinions about taking such action. One side advises against all tree root trimming; another allows for surface roots to be trimmed as long as they are a good distance from the base. I think the formula for the distance was three times the diameter of the trunk.
I would appreciate reading what y'all think. I'm including one picture from the street and another one front the front porch, showing another angle of the proximity of the trunk to the house through the garden.