Earlier maturity in cotton would counteract increasing production costs and facilitate the expansion of cotton production into areas with shorter growing seasons. Gaining earlier maturity without some yield penalty is difficult to achieve. Ultra-narrow row (UNR) cotton, a production system with rows spaced less than 40 cm apart, has shown potential for earlier maturity than conventionality spaced cotton (1m apart), without substantial yield penalties. In practice, this earlier maturity has been difficult to achieve consistently in UNR trials in both Australia and the United States. Information on the growth and development of UNR cotton is needed to find out why. A trial in southwest NSW near Hillston compared cotton in ultra-narrow (25 cm row spacing) and conventionality spaced rows. Despite greater dry weight and fruit production in UNR earlier in the season, the competition for light and resources later in crop development negated these early benefits and did riot translate into either earlier maturity or any increase in crop yield. The structure of the UNR cotton canopy meant that light was not penetrating through the top part of the plant to bolls lower in the canopy, perhaps delaying maturity. Studies are continuing into a greater range of environments and different population densities to further understand the key physiological processes of UNR production in order to optimise the system