Determining Poinsettia Nitrogen and Sulfur Fertilizer Application Rates Based on Chromometer and Sensory Panel Ratings

`Dark Red Annette Hegg' poinsettias (
Euphorbia pulcherrima
Willd. ex Klotzsch) were grown in a 1 peat : 1 perlite : 1 vermiculite medium using a pinched production schedule with varying N and S fertilizer application rates. Fifty-six treatments consisting of eight N levels (100 to 275 mg·L
−1
in 25-mg·L
−1
increments) and seven S levels (0 to 75 mg·L
−1
in 12.5-mg·L
−1
increments) were supplied. Other required nutrients were supplied at commercial recommendations for all treatments. Foliage of each plant was evaluated quantitatively by chromometer readings every 3 weeks. Marketability was determined by sensory evaluations from commercial producers, retailers, and consumers. Results indicated distinct color differences (hue, chroma, value) between S levels of 0 and 12.5 mg·L
−1
and a slight difference between S at 12.5 and 25 mg·L
−1
. The foliage of plants receiving 0 S was lighter, more vivid, and more yellow-green in color. As N levels increased, there was a linear response; foliage became more green, darker, and more dull. Commerical and consumer evaluators rated plants that received S at 0 or 12.5 mg·L
−1
at all N levels and plants receiving N at 100 mg L
−1
as unmarketable. This research indicates that `Annette Hegg' poinsettia requires S at a minimum of 25 mg·L
−1
and N at a minimum of 125 mg·L
−1
for commercial acceptance, and commercial N application rates may be greatly reduced when adequate S is supplied.