How deep do pine tree roots grow into the ground?

The important thing to note here is that all trees have root systems that extend horizontally at the soil surface, shallow, and wide, spreading several times wider than the width of the canopy. Most of the roots are found within the top few inches of soil, rarely extending deeper than 12 inches. The further away from the tree, the more shallow the roots are. Most trees start out with some sort of "tap" root. However, most trees tend to "lose" their deep roots as they grow. Conifers, especially pines, are generally an exception. They still have a vast and wide surface root system, but do grow a large tap root, which is esentially a downward extension of the trunk. It tapers quickly. I have dug pine tap roots out of the ground with excavators. At a certain point, it either breaks or you make the decision to cut it. The bulk of it is about 4 to 5 feet down, tapering rather quickly. I have seen tap roots over 12 feet long, tapering to a straw-size. I have had to cut large roots that seemed to never end. I suspect the limitation would hinge on soil type, water levels, oxygen levels, and soil density. I see no reason why a pine tap root wouldn't grow to 20 feet or more if conditions were right. But, remember the important surface roots before you go to trench.