Bench-Top Root Zone Heating: Can You Reduce Air Temperatures And Finish Bedding Plants On Time?

In the July issue of Greenhouse Grower, we discussed the effects of transplant date and the use of a row cover on cold-tolerant bedding plants grown in high tunnels, compared to conventionally heated greenhouses . In this article, we highlight another energy-efficient strategy: using bench-top root zone heating in combination with reduced air temperatures to finish bedding plants.

Soil, floor and bench-top root zone heating systems are by no means new technologies. In fact, the use of root zone heating dates back to as early as the 1970s. Bench-top root zone heating systems generally consist of a boiler or hot water heater, circulating pumps, distribution piping and thermostat controls (Figure 1). While these technologies were developed approximately 40 years ago, a survey conducted in 2008 revealed that only 7 percent of growers were using root zone heating.

Several studies conducted in the 80s and 90s stated that energy savings up to 50 percent could be achieved by using root zone heating in combination with reduced air temperatures, compared to perimeter hot water heating. However, a majority of those studies were conducted on cultivars that are no longer commercially available. To our knowledge, research-based information about specific combinations of air and root zone temperatures for several commercially important bedding plant species grown today is not currently available. Therefore, the objective of this study was to evaluate the effectiveness of root zone heating, in combination with reduced air temperatures, on the growth and development of nine commercially important bedding plant species with different cold tolerance classifications.

 

 

How This Study Was Conducted

Plant Material and Culture: Plugs or liners of cold-tolerant petunia ‘Dreams Midnight,’ pansy ‘Matrix Yellow,’ French marigold ‘Durango Bee,’ snapdragon ‘Oh Snap Pink’ and osteospermum ‘Serenity Bronze’; cold-intermediate seed impatiens ‘Super Elfin Lipstick’ and verbena ‘Aztec Blue Velvet’; and cold-sensitive: New Guinea impatiens ‘Celebration Red’ and vinca ‘Pacifica XP Rose Halo’ were received at Purdue University from a commercial greenhouse propagator (Tagawa Greenhouses, Inc.). Refer to our Basics and Beyond article on base temperatures in the July issue of Greenhouse Grower for more information about the cold-tolerance classifications.

Upon arrival, plants from each species were transplanted into 4.5-inch round containers filled with substrate comprised of 65 percent Canadian sphagnum peat moss, 20 percent perlite and 15 percent vermiculite. Plants were fertilized once a week with clear water supplemented with a water-soluble fertilizer (WSF), providing 400 ppm N.

Between each fertigation, plants were irrigated as necessary with acidified clear water, and leaching was kept to a minimum. The weekly application of a high-rate fertilizer was used to reduce any confounding variables that could have been associated with treatments receiving different rates of fertilizer, as a result of substrates drying out faster under higher root zone temperatures.

Greenhouse Environment: Plants were grown in two glass-glazed greenhouses with exhaust fan and evaporative-pad cooling and radiant hot water heating, controlled by an environmental computer. The photoperiod was a constant 16 hours, consisting of natural daylengths with day-extension lighting provided by high-pressure sodium lamps (HPS), which also delivered supplemental lighting to achieve a daily light integral (DLI) of 10 to 12 mol∙m–2∙d–1.

Temperature Treatments: The greenhouse air temperature set point was a constant 60°F for plants receiving root zone heating. Substrate temperature set points of 65°F, 70°F, 75°F and 80°F were achieved using independently programmable sections of bench-top tubing that circulated hot water from a high efficiency electric boiler (Figure 1), with an ambient treatment receiving no root zone heating serving as a control.

A separate greenhouse was used as a commercial control with a day/night air temperature set point of (12h/12h) 68°F/65°F and no root zone heating. Ten plants of each species were randomly selected, spaced equally in trays and placed on benches with or without root zone heating.

Can You Finish On Time?

Our results indicate that the time from transplant to first open flower of plants placed on root zone heating varies by species and cold-tolerance. For example, time to flower for petunia was delayed by 15, 13, 11, 6 and 4 days, respectively, as root zone temperature increased from 60°F to 80°F with an air temperature of 60°F, when compared to the commercial control with day/night air temperatures of 68°F/65°F (Figure 2). The delay in time to flower for most of the cold-tolerant species was minimal when they were grown on bench tops with root zone temperatures of 75°F or 80°F and an air temperature of 60°F.

For example, French marigold showed a 6- and 5-day delay and pansy showed a 6- and 1-day delay, respectively (Figure 3). However, time to flower of cold-tolerant snapdragon and osteospermum was delayed by 9 and 14 days, respectively, at root zone temperatures of 75°F and 80°F (Figures 4 and 5). As expected, time to flower of cold-sensitive New Guinea impatiens and vinca was significantly delayed with root zone heating. Additionally, chilling injury made the New Guinea impatiens unmarketable.

Shoot tip temperature primarily controls the rate of development (i.e., leaf unfolding rate, days to first open flower) and, to a lesser degree, substrate temperature. Therefore, we postulate that species that have a prostrate or shorter growth habit are best suited for root zone heating production.

Our results indicate that cold-tolerant petunia and French marigold can be produced with limited delay in flowering time, while maintaining quality, compared to the commercial control if root zone temperatures of 75°F or 80°F are achieved with a reduced air temperature of 60°F.

What About Energy Savings?

We used USDA’s Virtual Grower software to estimate potential energy savings a grower may achieve by producing a petunia crop in a double poly greenhouse located in Indianapolis, Ind., with a projected market date of March, 10, April 10 and May 10.

It estimated that a grower could reduce heating costs by 20 percent, 16 percent and 15 percent, respectively, by reducing the air temperature from 68°F/65°F to a constant 60°F with an added four days of production. These estimates are reduced for every day the crop is delayed. At a certain point, any savings that could be achieved by lowering the air temperature will be negated and eventually will require more energy.

If we were only considering the cost to grow under reduced air temperatures, the energy savings may be high enough for a grower to consider installing a bench-top root zone heating system. However, growers must consider the other costs associated with using root zone heating in combination with reduced air temperatures, such as the expense of operating a boiler or hot water heater. Unfortunately, with our system, we were unable to quantify the amount of energy that would be necessary to operate our boiler to heat the root zone to 75°F or 80°F.

The energy used to run a boiler or hot water heater to heat the root zone would reduce the 15 to 20 percent savings, not to mention the additional cost to install the system and potential return on investment. However, for growers who already have root zone heating systems installed, this study may give you a better idea of the substrate temperatures needed to grow bedding plants under reduced air temperatures. This study may also help growers who already have a system installed, select crops that respond positively and avoid crops that we found to not benefit from root zone heating.

The authors thank Ball Horticultural Co., Everris, Fafard and the Indiana State Department of Agriculture Specialty Crop Block Grant 205749 for supporting this research.

Topics: ,

Leave a Reply

One comment on “Bench-Top Root Zone Heating: Can You Reduce Air Temperatures And Finish Bedding Plants On Time?

  1. Would have enjoyed reading the article if not for your annoying join the newsletter pop up that can’t be removed so one can continue reading……..

More From Equipment...
PP&L CAST 2015 intros

April 22, 2015

6 Breeding Companies Serve Up New Varieties At Pacific Plug & Liner

Pacific Plug & Liner’s theme this year, Labyrinth, a conservatory of the world’s most captivating plants, was perfectly topped off (pun intended) with fascinators for the women and newsboy caps for the men. The PP&L team dressed their part to act out the gothic “conservatory of the world’s most captivating plants.” Truly, the displays looked like they practically popped out of a catalog, and the costumes were a nice touch. Retailers take heed, the fully merchandised displays at Pacific Plug & Liner are worthy of emulating. We’ll let the pictures tell the story of all the fabulous variety introductions presented at  Pacific Plug & Liner’s 2015 California Spring Trials, where Cultivaris, Cohen Nurseries, Histil Nurseries, Jaldety Nurseries, Southern Living/Sunset Collection and Pacific Plug & Liner all highlighted their 2016 introductions.  

Read More
Speedling 2015 CAST intros

April 22, 2015

Speedling Inc. Presents New Varieties From ABZ Seeds, Hem Genetics, Thompson & Morgan, Vista Farms & PSI

You name it, we saw it at Speedling's California Spring Trials location in San Juan Bautista, where five companies showed off their new introductions for 2016.

Read More
PittMoss on Shark Tank

April 22, 2015

PittMoss Wins On Shark Tank

Mont Handley, president and CEO of PittMoss, appeared on ABC’s Shark Tank on April 17 to try to get the “sharks” to invest in his peat moss alternative. Three investors from the TV show contributed $600,000 to PittMoss for a 35 percent stake in the company. Check out this clip from ABC’s website in which Mark Cuban, Kevin O’Leary and Robert Herjavec discuss getting on board with the product. PittMoss is an alternative to sphagnum peat moss, made up of a mix of proprietary additives and recycled paper rescued from landfill space. Handley founded the Pittsburgh-based company in 1994. What started as a small experiment grew into a full-fledged business with the help of funding provided by an EPA SBIR grant and Pittsburgh’s Idea Foundry. Today, PittMoss is available to commercial greenhouses and nurseries from Michigan to Maine to North Carolina, with plans to grow. To learn more, visit PittMoss’ website, or check it […]

Read More
Latest Stories
Growers are looking for low-cost options for temperature control, like circulating fans and exhaust fans.

April 10, 2015

New Ways To Give Growers Control Of The Greenhouse Envi…

From heating systems to circulation fans, manufacturing companies are finding new ways to help growers control the greenhouse environment, save on energy costs and streamline production.

Read More
Polyarch Berns

March 12, 2015

The Energy Efficient Greenhouse

New coverings technology means today’s films, plastics, shade cloths and climate screens slash heating and cooling costs while improving crop productivity year round. We checked with manufacturers to see what’s new and uncovered some best practices for buttoning up your greenhouse. Here’s what you need to know about the latest trends.

Read More
FormFlex_MTZ Hanging Basket

March 11, 2015

4 New Ways To Automate Your Operation

These new automation products can help streamline labor-intensive tasks, saving time and labor and increasing productivity.

Read More
Outfitting Your Greenhouse

February 24, 2015

Save Energy With The Right Greenhouse Glazing

The glazing you choose can make a big difference in your energy bill and the uniformity of your crops.

Read More
Michigan State University Extension

February 24, 2015

Ethylene From Defective Greenhouse Heaters Damages Crop…

Malfunctioning greenhouse heaters can lead to crop damage from ethylene and carbon monoxide induced illness for workers. Michigan State University's Extension educators Tom Dudek and Randy Beaudry teach you how to recognize the symptoms and check greenhouse heaters to avoid the concern.

Read More
Havest Automation Robot

February 18, 2015

Robots Grab Hold Of Growers’ Material Handling Needs

Harvest Automation’s HV-100 robots automate one of the hardest, most labor-intensive jobs at growing operations – plant spacing. With more technology coming, investing in robots could become even more realistic for growers of all sizes.

Read More

February 1, 2015

4 Lighting Products For Your Operation

These new lighting products have been developed for maximum energy efficiency in greenhouse production. Check out the slideshow to see which products are right for your operation.

Read More
LumiGrow

January 30, 2015

LumiGrow Expands Customer Base In 2014

LumiGrow, Inc. is adding more than 125 new commercial, governmental and research customers to its roster of customers, and beyond the new accounts added this year, many existing customers significantly increased the number of LumiGrow products they use and research customers made LumiGrow a part of their efforts to add to the body of knowledge about spectral science.

Read More
harvest automation featured image

January 13, 2015

Harvest Automation Extends Robot Rental Program

Harvest Automation's robot rental program proved to be such a success for the company that it is being extended through the spring. The program was unveiled last year as a way for customers to get started with HV-100 robots.

Read More

January 9, 2015

Innovations In Irrigation

Need help improving your irrigation? Check out these new products.

Read More

December 2, 2014

Hanna Instruments, Inc. Introduces pH Electrode With Bl…

Hanna Instruments recently released HALO, a professional pH probe with Bluetooth Smart (Bluetooth 4.0) technology that transmits measurement data directly to an Apple iPad running the Hanna Lab App.

Read More

November 24, 2014

Biomass Six Years Later: Would Pleasant View Do It Agai…

Pleasant View gardens installed its first biomass boiler six years ago and has added a second one since. Now it’s reaping the benefits of lower heating costs and dollars saved.

Read More

November 18, 2014

7 New Media And Light Products For Greenhouse Productio…

New media and light products cover a broad sweep of growing conditions.

Read More

October 21, 2014

GreenClocks New Generation City Farm Fitted With Philip…

Osaka Prefectural University’s new city farm, which has been fitted out with Philips LEDs, opened September 19.

Read More

October 1, 2014

Harvest Automation Introduces Robot Rental Program

Harvest Automation has unveiled a new introductory robot rental program as a way for customers to get started with HV-100 robots.

Read More

September 15, 2014

Precision Horticulture: What Piece Of Equipment Or Syst…

Let us know what product you can't live without.

Read More

September 15, 2014

New Products For Precision Growing

Increase efficiency with these new offerings in equipment, automation, structures and software.

Read More

August 12, 2014

LEDs Comparable To High Pressure Sodium Lamps For Cutti…

In his Cultivate'14 presentation on lighting the future of young plants with LEDs, Christopher Currey, Iowa State University, shared recent research on how LED lights stack up against high pressure sodium lamps for liner and plug production.

Read More