What is a Tap root? These particular tap roots are from Common Mallow Plants (Malva neglecta)(weed). Notice the length of the roots (the length of the pocket knife is 3 1/2 inches). Plant roots take many shapes which have evolved over time. Sometimes the roots only spread out just below the soil surface in a circle around the center of the plant. If the roots encounter an obstruction like a rock, then they find a different direction to take. Roots are on a constant search to find water and nutrients. Tap roots develop going straight down into the soil and often send out lateral roots. Plants with tap roots do well in dry conditions where moisture is only found deep in the soil. Tap roots create channels in the soil which later remain after the plant has died. These remaining channels in the soil facilitate water absorption deep in the soil, especially in heavy or compacted soils.