Cotton's indeterminate growth habit reduces the efficiency of yield formation when grown as an annual for its lint. Altering the determinacy may provide greater carbohydrate partitioning to reproductive structures, allowing higher yields. Another factor that may influence partitioning is potassium (K) nutrition. It is essential for physiological and biochemical processes including translocation. A two-year experiment was conducted at the West TN Experiment Station to evaluate carbohydrate partitioning in PM1218BG/RR, a relatively determinate cultivar, and DP555BG/RR, a more indeterminate variety; under two levels of potassium fertilization (60 and 120 lb K2O/ac/yr). Plots containing cultivars and K treatments were arranged in randomized complete blocks with six replications per year. Plant samples were harvested at early bloom and after cutout, to evaluate partitioning during reproductive development. Eight stem samples per plot were collected immediately below the cotyledonary node, freeze dried, and ground for carbohydrate analysis by enzymatic methods. Results showed that K treatments had significant effects only on monosaccharide concentrations. Sucrose concentrations were higher in DP555 than in PM1218 at early bloom but declined to equivalent concentrations after cutout. Starch analysis also revealed both a cultivar difference and harvest date interaction. Where PM1218 had higher initial stem starch concentrations that declined with boll loading, DP555 starch concentrations increased. Relating these results to shoot biomass data, collected at both harvest dates, confirms that determinate variety PM1218 allotted more photoassimilates for reproductive growth during this time, despite similar lint yields. Two hypotheses may explain the observed differences: (1) the determinate variety may have a lower root-to-shoot ratio than the indeterminate, and (2) PM1218 may have a higher reproductive sink strength than DP555, due to higher seed oil content. This information provides a better understanding of cotton's use of soluble sugars and labile starch reserves to accommodate both vegetative and reproductive requirements.