Transpiration rates of chrysanthemum [Dendranthema x grandiflorum (Ram
at.) Kitamural plants grown under spectral filters were evaluated as p
art of an investigation on using light quality to regulate plant growt
h. The 6% CuSO4.5H2O spectral filter reduced photosynthetic photon flu
x density in red (R) and far red (FR) wavelengths and increased the R
: FR and blue (B) : R ratios (B = 400 to 500 nm; R = 600 to 700 nm; FR
= 700 to 800 nm) of transmitted light relative to the water (control)
filter. After 28 days, cumulative water use of plants grown under CuS
O4 filters was almost-equal-to 37% less than that of control plants. T
ranspiration rates were similar among plants grown under CUSO4 and con
trol filters when expressed as leaf area, a result suggesting that the
reduced cumulative water loss was a result of smaller plant size. Pla
nts grown under CUSO4 filters had slightly lower (10%) stomatal densit
y than control plants. Light transmitted through CUSO4 filters did not
alter the size of individual stomata; however, total number of stomat
a and total stomatal pore area per plant was almost-equal-to 50% less
in plants grown under CuSO4 filters than in those grown under control
filters due to less leaf area. The results suggest that altering light
quality may help reduce water use and fertilizer demands while contro
lling growth during greenhouse production.