- In situ measurements of leaf water potential by thermocouple psychrometers are useful in monitoring the energy state of water in plants. Excessive equilibration times caused by low vapor conductance across the leaf cuticle and vapor sorption in the psychrometer chamber often make in situ sampling difficult. Several methods of removing the waxy leaf cuticle have been shown to increase water vapor conductance across the epidermis of the leaf, but their relative effectiveness has not been compared and equilibration times are unknown. Six wax removal treatments were compared with an untreated control to determine the most effective technique for increasing water vapor conductance across the leaf surface. The mean time for the leaf psychrometer to reach an equilibrated water potential was estimated for the treatment that produced the greatest conductance. Abrasion treatment of leaves with 600 grit sandpaper produced the greatest increase in cuticular conductance, resulting in a mean equilibration time for psychrometer measurements of 7.5 min.