Water uptake through the fruit surface is an important factor in cracking of sweet cherry fruit (Prunus avium L.). The objectives of this study were to (1) provide evidence for polar pathways across the sweet cherry exocarp, (2) investigate the effect of selected salts on water uptake, (3) establish the mechanism of Fe-salts in reducing water uptake, and (4) determine whether Fe-salts are suitable for applications under field conditions. (1) Water uptake through the exocarp of intact cherry fruit was determined gravimetrically using an immersion assay. The osmotic water permeability (Pf) of the exocarp was linearly related to the inverse of viscosity of the incubation solution. When fruit were incubated in isotonic solutions of selected osmotica, water uptake decreased and the apparent water potentials increased as molecular weight of the osmotica increased. The self diffusion permeability (Pd) of exocarp segments (ES) and isolated cuticular membranes (CM) for radio labeled substances was determined using an Infinite-Dose-Diffusion system. The Pd of sweet cherry ES for 1-naphthyl[1-14C]acetic acid (NAA, pKa = 4.2) and the activation energy (Ea) of NAA penetration was significantly higher for the predominantly undissociated (lipophilic) NAA (pH 2.2) than for the predominantly dissociated (polar) NAA (pH 6.2). These data provide evidence for the presence of porous polar pathways through the cherry exokarp that allow water uptake by viscous flow. (2) The rate of water uptake (F) in cherry fruit was reduced in the presence of some mineral salts (10 mM). The largest decrease in water uptake (-40 to -60%) was achieved, when fruit were incubated in CuCl2, HgCl2, AlCl3 and FeCl3. (3) The mechanism of FeCl3 in decreasing water uptake was investigated using the Infinite-Dose-Diffusion technique. Adding FeCl3 (10 mM) to the donor decreased Pd of cherry ES for 3H2O by about 60%. The decrease in Pd of 3H2O always required the presence of a pH gradient between the FeCl3 donor and the aqueous receiver solution. FeCl3 also decreased the Pd for NAA and 2,4-dichloro[14C]phenoxyacetic acid (2,4-D, pKa = 2.6) through cherry ES. The decrease was larger for the predominantly dissociated (polar, pH 6.2) than for the undissociated (lipophilic, pH 2.2) acids. The data suggest that FeCl3 decreased transport of water and other polar substances by a pH-dependent precipitation reaction that occurs in the polar pathways across the sweet cherry fruit exocarp (see 1). (4) Characteristics that are relevant for spray application of Fe-salts in the field were investigated using laboratory immersion assays and cracking tests. FeCl3 decreased water uptake through microcracks in the exocarp, but had no significant effect on uptake through holes in the exocarp or on uptake along the pedicel/fruit juncture. The reduction in fruit cracking obtained after spray application of FeCl3 and Fe(III)-glucoheptonate in the field was markedly smaller than that after incubating fruit in the solutions of the Fe-salts. Unfortunately, Fe-salts caused severe black discoloration of fruit that is inacceptable from a marketing point of view. Nevertheless, the identified mechanism of decreasing water uptake by a precipitation reaction that plugs polar pathways across the exocarp is a promising strategy for reducing fruit cracking.