I have a massive sago palm that I am removing because it is taking up too much space in a small area. It is actually about 4 different ones, as it seems that pups were left on the plant and had began to grow large. I have already started the job, and have removed the foliage and the stems above ground. Is this good enough to kill the plant, or do i need to dig the root ball out? If I do have to dig it out, does anyone have an approximation of how deep I will have to dig? After removing the foliage and stems I am left with a footprint of about 3.5' of where the plants were located and the largest stem was about 24" long. Thanks.