About 20 years ago we planed a dogwood tree in one of our planter beds. Since planting the tree it has sent root suckers all throughout the garden, and they extend about 20' away. The tree died in an ice storm a couple years ago and was removed, but the suckers continue to grow and are overtaking everything else in the garden. Historically, I've cut back the suckers and in some cases chopped out the roots (sucker base root) to remove them, but they are quite persistent and seem to be able to propagate from an existing portion of a root. Is there any way to get rid of these once and for all? Unfortunately, I don't recall the type of dogwood, but it looked similar to a Gray dogwood (swamp dogwood). Thanks in advance for any advice!