Hydrangea (Hydrangea macrophylla) is a widely cultivated ornamental nursery crop, but its vigorous shoot growth often necessitates labor-intensive pruning or repeated applications of plant growth regulators (PGRs) to achieve saleable quality. As a result, methods to reduce reliance on pruning or PGRs are highly desirable to growers. One potential alternative is the use of shade netting, which is commonly used in nursery production to protect sensitive plants from excessive solar radiation. This includes hydrangeas which are frequently grown under 30–50% black shade netting. Beyond reducing light intensity, shade nets can also alter the light spectrum, adjusting the relative quantities of blue (400–499 nm), green (500–599 nm), and red (600–699 nm) light, which may affect plant morphology. Blue shade nets, which primarily absorb green and red light, are often marketed as tools to produce more compact shoot growth and thus could serve as an alternative to pruning or PGRs. However, little information exists on the use of blue shade netting to control hydrangea shoot growth. This study evaluated the effects of shade color (black, blue, red, and grey) and blue shade percentage (40–75%) on the growth of hydrangea ‘Twist and Shout’ in a nursery and a greenhouse trial. In the nursery trial, hoop houses were covered with either 30% black, 30% blue, 30% red, or 45% grey shade netting. In the greenhouse trial, chambers were covered with either 40% blue, 50% blue, 75% blue, or 50% black shade netting. Growth parameters including canopy height, width, volume, projected canopy area, leaf length, and chlorophyll concentration were measured repeatedly over a 49-day growth period. Results from the nursery and greenhouse trial showed that shade percentage, not shade color, was the dominant factor influencing shoot growth. Thus, colored shade netting did not suppress plant vigor or reduce the need for pruning or PGRs. These findings suggest that 30% black shade was ideal for hydrangea production, and altering the color of shade netting provided no additive benefits. While ineffective for hydrangea production, nursery crops that benefit from higher percentages of shade such as Hosta plantaginea, may benefit more from colored shade netting.
