Permanent wilting point (PWP) or wilting point (WP) is efined as the minimal point of soil moisture the plant requires not to wilt. If moisture decreases to this or any lower point a plant wilts and can no longer recover its turgidity when placed in a saturated atmosphere for 12 hours. The physical definition of the wilting point (symbolically expressed as θpwp or θwp) is defined as the water content at −1500 J/kg (or −15 bars) of suction pressure, or negative hydraulic head.