It's starting to look a lot like Christmas inside one special New Mexico State University greenhouse. An experimental crop of poinsettias are coming into their red glory just as a six-month study to optimize greenhouse water and fertilizer use winds down in time for Old Saint Nick.
"Poinsettias aren't easy to cultivate," said Geno Picchioni, an NMSU horticulturist. "They require significant greenhouse space per plant, pinching at specific times to promote branching and lots of water."
Poinsettias are the best-selling potted plant in America--even though most people only buy them during the holidays. In New Mexico, poinsettias are a critical part of the greenhouse industry. Nurseries statewide produced some 493,000 poinsettia pots valued at $1.9 million last year, according to U.S. Department of Agriculture National Agricultural Statistics Service.
To fully appreciate the promise of poinsettias, 15 horticulture students signed on this fall for a senior level horticulture course in greenhouse management. The class gives students hands-on experience in operating a greenhouse, but this year their professor added a holiday twist.
The students' task was to precisely track water loss and fertilizer uptake in 140 poinsettias. Two popular varieties were chosen: Festival Rose and Silver Star Red. In addition to keeping a sharp eye on water use, three different fertilizer treatments were monitored. The plants were weighed daily, and each was adjusted to prescribed water and fertilizer levels.
The poinsettias were planted in greenhouses, at the end of July, at NMSU's Fabian Garcia Research Center, just west of the main campus. They are expected to reach full bloom on Dec. 1. From their start as three-inch plugs, the poinsettias have reached heights of 15 inches and are growing in six-inch pots.
"The students just eat this greenhouse experience up," Picchioni said. "But this is a lot more than traditional grow and show. This time they're really addressing a deficit in the scientific literature. We're going to have a much better understanding of optimal poinsettia water and fertilizer use after this project."
The project is funded through a grant from the Rio Grande Basin Initiative, a joint project between NMSU and Texas A&M University to study and teach about water conservation and quality along the Rio Grande corridor.
The challenge for the NMSU students was maintaining the plant's water weight. "We didn't want the soil water content to fall below 40 to 50 percent of capacity," said Kim Fields, the students' laboratory instructor. "With greater amounts of water depletion, the plant begins to show signs of water stress, changing color from dark green to light tan."
Results on the poinsettias' water and fertilizer use will be shared with the state's small- and medium-scale greenhouses. These growers with operations under an acre are most likely to use traditional greenhouse irrigation methods--drip plastic tubing or hand watering.
"These are essentially open systems, which potentially can waste water and fertilizer," Fields said. "The smaller growers can't afford automatic irrigation systems with recycling capabilities that many of the big growers have, which is why this new data is so important."
Poinsettias were introduced to America in the 1820s by Joel Roberts Poinsett, the first U.S. ambassador to Mexico.
Consumers snap up the bulk of the poinsettias during a short, frantic selling season from early November to just before Christmas. Red is the most popular color, representing 75 percent of poinsettias sold in 2003, according to the Society of American Florists. Coming in a distant second was pink, followed by white.
As Christmas nears, the sea of poinsettias brightening the NMSU greenhouse will fade as the lab portion of the study ends and students hold their annual holiday plant sale. Their pampered poinsettias will be sold to help pay for future research and teaching projects.