On a day when the outside temperature hovers around freezing, Dan Pierson's greenhouse is about 74 degrees with 86 percent humidity.
The heat comes from hot water pipes embedded in the concrete floor. The humidity comes from the tomato plants absorbing the water from the nutrient solution their roots are submerged in, then emitting it from their leaves.
Pierson is a retired grain farmer turned hydroponics farmer, the Independent of Marshall reported.
"Hydroponics is growing plants without soil," Pierson said. "The plants absorb nutrients obtained from the water."
Rows of tomato plants are rooted in planters full of inert gravel. The nutrient solution trickles in from the top and drains out of the bottom of each planter. The water then flows back to the holding tank where it is topped off with more nutrients before being recycled. The temperature is controlled by thermostats buried in the media with the roots.
The nutrient mix is very precisely balanced, according to Pierson. He mixes each batch from ingredients he weighs on a laboratory scale. Most of the mix is carbon, hydrogen, oxygen, and nitrogen contained in various compounds. But there are a total of 16 essential elements, some of which need to be present only in very small amounts.
The proportion of ingredients in the nutrient solution itself must be adjusted for light conditions, length of the day, etc. And the plants can be finicky about the water, too. Though hydroponic plants can use untreated local water in some places, Slayton municipal water is not suitable.
"Everyone who wants to do hydroponics has to check the water first," Pierson said. "The strength of a fertilizer solution is measured in electrical conductivity. Fertilizers are salts, solutions of positive and negative ions. The stuff in the well water is not the right balance of what the plants need and plants can't take up water if there's too much conductivity."
So Pierson passes water from the municipal system through a water softener and a reverse osmosis filter, which produces a gallon of pure water with zero conductivity from every two gallons that come in.
The question arises then of why go to all this trouble?
"I get a lot more produce than growing out-of-doors," Pierson said. "I can harvest continuously from April to November, in theory."
The tomatoes Pierson grows are indeterminate varieties that continue to fruit and grow vegetatively and reproductively year-round — as opposed to determinate bush varieties that grow outdoors.
Another advantage is they can be harvested when ripe and distributed locally, rather than unripe and artificially ripened in ethylene gas chambers.
"Tomato plants in grocery stores are all picked unripe," Pierson said. "They never get ripe, won't develop sugar and won't taste right."
Pierson markets his tomatoes to local restaurants, hospitals and schools throughout southwest Minnesota.
Page 2 of 2 - "They're excellent, there's no comparison to what you can buy," said Cathy Rogers, food service director for the Pipestone Area School District. "We go through 40 percent more tomatoes when we buy from him than when we buy from vendors."
Pierson built the greenhouse on The Three Acre Farm in Slayton with his own hands and only minimal part-time help, except for the concrete floor and the electrical system. Next to the tomato greenhouse he's building a much simpler greenhouse without a concrete floor, fan or heating system.
"It's just a season extender," Pierson said. "This summer I'm going to put the plastic on the frame and grow green beans."
Pierson has worked as a chef and still works part-time as a painter. He said he build his hydroponics operation because he wanted something he could run by himself without help or partners.
"I don't make much money at it, but I love doing it." Pierson said.