In 1991 and 1992, four Upland cotton genotypes were planted at two-week intervals from mid-April to mid-May in Florence SC. Harvest dates were similarly staggered so that mean season lengths were 150 d (1991) and 170 d (1992). When fiber characteristics of 'Deltapine 20, 50, 90, and 5690' were quantified by AFIS, mean fiber diameters, perimeters, cross-sections, circularities, and micronaires decreased from earliest to latest planting. Mean fine fiber fractions and immature fiber fractions increased with Julian planting date in all genotypes. The planting-date related variations in cotton fiber quality persisted through yarn spinning and dyeing where environmental effects on fiber maturity increased yarn elongation percent and decreased evenness of dye uptake. Strong relationships were found between fiber quality [maturity] and cumulative heat units (degree-day-16°C) approximately at pre-bloom (50 days post planting) or post-cutout (100 days post planting).