Abstract During the second summer after planting, average weekly height growth of 72 sample trees of intensively cultured Populus deltoides Bartr. in southern Illinois ranged from zero in mid-April and early October to nearly 10 inches during the last half of July. The curve of current growth was bell-shaped and followed closely the curve of minimum air temperature. The cumulative growth curve was sigmoid. Soil moisture was plentiful in the deeper layers of alluvial soils, and the relatively low soil moisture in the shallow layers at the end of July corresponded with maximum height growth. Current growth was also related to weekly average and maximum air temperature but not to relative humidity, vapor pressure deficit, or tree height at the beginning of the summer. Most trees started height growth the last week in April, but the time when growth ceased ranged from the week ending August 17 to the one ending October 5. Half of the trees were still growing after September 14. Growth cessation was apparently under strong genetic control.