By EMMA HOPKINS-O’BRIEN

Indiana Correspondent

WEST LAFAYETTE, Ind. — Last month at a Purdue University-hosted Greenhouse and Indoor Hydroponics workshop, attendees learned optimal hydroponic techniques for growing lettuce, including nutrient, temperature, lighting, pest control, disease management considerations and varied production systems.

Hydroponic farming is a method of growing food using little to no soil, and by placing plants in nutrient-infused water which is then circulated constantly through all plants in the operation. A Purdue expert in controlled environment agriculture, Krishna Nemali, headed the workshop and spoke on the importance of temperature in winter hydroponic crops and how growers can calculate their heating costs before the winter season to determine potential income.

“There is a value in producing a crop over the winter,” Nemali said. “Temperature has a big influence on both the growth and development of crops. When you add heat, you can produce a better crop. But when you add heat, you pay for it. And if you’re paying for it, you better know how much you’re paying.”

Heat is lost from greenhouses sheltering hydroponic crops in the winter, specifically through conduction and long-wave radiation, Nemali said. Orienting greenhouses properly according to the position of the sun is one way to mitigate this, but electrically heating a greenhouse will produce the best crop.

Nemali explained that calculating heating costs over the winter is necessary and possible – and he has formulated an equation to do just that, which uses the values of heat needed, heat transfer coefficient, surface area and the difference between inside and outside temperatures.

“I know one thing: I don’t want to invest in something if I don’t know how much it’s going to cost to produce it,” he said. “If it’s going to be a biting-cold winter, do you know how much your heating costs will be? Do you know how to do the math?”

During the hands-on portion of the workshop, visitors were able to walk through various stations of the Purdue Horticulture greenhouse, each featuring a different method of hydroponic growing. Nemali’s station demonstrated vertical farming, in practice, to facilitate an experiment testing different LED light types on lettuce plants.

A benefit of vertical farming, he said, is the limited amount of space the operation needs to function. By stacking trays of hydroponic-grown plants on top of one another under artificial lights, hundreds of plants can fit in a space which could horizontally only hold a few.

According to Petrus Langenhoven, a horticulture and hydroponics specialist, one of the most important considerations of hydroponics is the nutrient formula. He said numerous published formula options exist for hydroponic growers, but different crops have different needs.

“For vegetative crops, most nutrient-solution recipes don’t adjust the ratio of nutrients while they grow,” Langenhoven explained. “In fruiting crops, the ratio may be adjusted to alter the shift between vegetative and reproductive growth.”

He said for growers new to hydroponic farming, using one recipe that works well for a range of crop growth stages and conditions is a good idea.

Another station in the greenhouse tested hydroponic plots receiving various concentrations of nutrient. Alex Miler, a Purdue graduate student in horticulture, conducted the experiment, which used 24 varieties of lettuce, two types of hydroponic systems and four different concentrations of fertilizer.

“My main goal was to optimize hydroponic production of lettuce in the Midwest/Indiana area,” Miler said. “I’m looking at the nutrient uptakes of the most popular lettuce varieties in this area.”

Langenhoven had his own station that grew a plot of pepper plants, grown hydroponically in very poor soil and vines tied and suspended from a trellis.

Purdue’s Department of Horticulture and Landscape Architecture, responsible for organizing the workshop, encourages anyone interested in hydroponics and other sustainable horticulture topics visit its website at www.ag.purdue.edu/hla/extension or Facebook page to learn about future workshops and programs.