What is Root Pressure?

Root pressure is the upward force that helps push water and nutrients from the roots to the rest of the plant, especially through the xylem tissue. Root pressure happens when minerals are actively taken up by the roots from the soil. This process increases the concentration of solutes inside the root cells, which causes water to enter the roots through osmosis. 

As a result, a positive pressure is built up inside the root system, pushing water upwards into the xylem vessels. This pressure is most noticeable at night or early morning when transpiration (loss of water from leaves) is low or not happening. In such times, you may even see droplets on the tips of leaves. This is called guttation, and it is evidence of root pressure.

Although root pressure alone is not strong enough to lift water to the top of tall trees, it plays an important role in small plants and during the early part of the day before transpiration begins.