How Dirty Is Your Water? Ready Research Results

During summer 2009, we collected irrigation water samples from 24 greenhouses and nurseries across 11 states in the United States as part of the Young Plant Research Center program. We evaluated physical, chemical and biological water quality and determined whether current treatment practices were maintaining water quality within recommended guidelines.

Table 1 summarizes our results for up to the five types of samples we collected in each location:

• “Source” water samples were the municipal or well supply collected at the first access point after entering the greenhouse.

• “Furthest outlet” samples were collected from a boom, emitter or hose after traveling within the irrigation plumbing the furthest distance from the “source.”

• “Bench and floor” samples were collected from ebb and flood irrigation water before treatments such as filtration were re-applied to the return water.

• “Tank” samples represented irrigation water stored in concrete-lined tanks indoors. Samples had been treated with acid, descaling chemicals, fertilizer, filtration or sanitizing agents.

• “Pond” samples were from open, outdoor catchment basins receiving runoff and return irrigation water.

Water quality has physical, chemical and biological components. When any of these factors are out of range, problems may occur with plant health or the efficient functioning of equipment.


• High suspended solids from peat or sand particles can clog equipment and are a measure of the adequacy of filtration. In our survey, suspended solids were below the EPA-recommended range of 20 mg/L for non-edible crops, except for a small number of “tank” and “furthest outlet” samples.

• The clarity of water in terms of transmission of ultraviolet (UV) light is important as to whether UV radiation would be effective to sanitize water. UV transmission was above the recommended minimum 75 percent level in all but one “source” water. However, more filtration would be needed in many of the other sample types, such as “pond” water, for UV radiation to be effective.


• Irrigating with water containing high alkalinity will cause pH in the growing medium to rise over time, because alkalinity represents dissolved lime. Alkalinity levels in “source” water ranged from 0 to 323 mg/L CaCO3, with acid injection needed in many locations to neutralize alkalinity.

• Water pH is important in terms of solubility and activity of chemicals. Source water in more than half of the locations had pH levels above 7.5, which indicates a need to inject acid when using chemicals such as copper ionization or chlorine, in order to increase their sanitizing power.

• Electrical conductivity (EC), which is a measure of the total ion concentration, tended to be low in “source” water. This is not surprising given that all of the surveyed growers were propagating plugs or liners, which are particularly sensitive to salts. Reverse osmosis or blending of water sources would be suitable in one rooting station greenhouse that had a “source” EC level of 1.2 mS/cm.


• Total aerobic bacteria, in colony forming units per milliliter (cfu/mL), is a measure of microbial activity in the water. Bacteria count is useful to indicate biofilm (bacteria, algae and other microbes) on the inside of irrigation lines and the risk of equipment clogging. The large increase between the “source” and “furthest outlet” bacteria counts occurred mainly because of biofilm inside the irrigation lines. Counts below 10,000 cfu/mL are recommended to avoid clogging issues. Only 10 percent of the “source” samples exceeded 10,000 cfu/mL, but high levels were found in other parts of the irrigation system, especially in “pond” water. For growers spending a lot of labor unclogging emitters, a high bacteria count indicates the need for injection of a sanitizing agent.

• Most aerobic bacteria are likely to be benign or beneficial and are not plant pathogens. The higher the bacteria count, however, the higher the demand for a sanitizing agent such as chlorine to control biofilm – and the less likely the sanitizer will be effective against target pathogens such as Pythium.

Overall Sanitizing Demand

• For this measurement, we dosed the water sample with a known amount of chlorine (as bleach, which is sodium hypochlorite), and two minutes later measured free chlorine. This “chlorine demand” value represents how much sanitizing agent would be needed to oxidize contaminants in the water. The demand also represents how much chlorine would need to be injected to achieve a target-free chlorine level of 2 mg/L, which is generally recommended by plant pathologists for Pythium and Phytophthora control.

For example, with “pond” water, if the target was 2 ppm of free chlorine, an average of 3.2 + 2 mg/L = 5.2 mg/L would be needed because of organic matter, fertilizer and other material in the water. Note the high chlorine demand in the “tank” samples. This occurred in part because most of the “tank” water included ammonium fertilizer, which creates a large demand on chlorine.

For more information on this and other water quality and treatment topics, see our resources at the industry-sponsored website,

Leave a Reply

More From Plant Culture...

November 26, 2015

2015 Metrolina Greenhouses (Huntersville, NC) Field Trials Results

See the 2015 field trials results for Metrolina Greenhouses in Huntersville, NC.

Read More
Yoshimi And Grace Shibata

November 26, 2015

American Floral Endowment Establishes Fund To Honor Legacy Of Yoshimi Shibata

Yoshimi “Shimi” Shibata, a flower grower and wholesale florist, passed away in October at the age of 100.

Read More
Vinca 'Valiant Lilac' (2015 Texas A&M University Field Trials)

November 25, 2015

2015 Texas A&M University (Overton, Texas) Field Trials Results

See the 2015 field trials results (includes photo gallery) for Texas A&M AgriLife Research and Extension Center in Overton, Texas.

Read More
Latest Stories

September 20, 2015

Technology Improves Orchid Production At Green Circle G…

Green Circle Growers in Oberlin, Ohio, has a commitment to using production practices that are efficient and sustainable. The operation has been growing Orchids for nine years, and is entering its second full year with its current system, which entails three camera grades. “The camera grading — first at production into a 5-inch pot, then 12 weeks later and a final grade after the stem and buds have developed — is raising our overall quality,” says Wesley Van Wingerden, director of growing for Green Circle Growers. Greenhouse Grower visited the operation to take a tour of its facilities and learn more about its Orchid production. Read on for more details about the process. The first of the camera grades is incorporated into the transplant process, which involves placing the Orchids from a community tray into 5-inch pots. The plants are separated into three sizes with the smallest returning to the […]

Read More

September 15, 2015

Young Plant Growers Weigh In On Crop Gains, Sales Trend…

Almost 100 young plant producers participated in Greenhouse Grower’s 2015 Young Plant Grower Survey, which asked growers questions abot crop categories, sales, order fulfillment and more.

Read More
Top20YPGrowers feature image

September 15, 2015

The State Of The 2015 Young Plant Market

Young plant growers in North America are changing their strategies to stay competitive in today’s market. Here is how 2015 shapes up in trends and statistics.

Read More
Vivero International_Endisch

September 8, 2015

Vivero Internacional Continues To Expand Unrooted Cutti…

The tenth largest cuttings farm in the world, Vivero Internacional was founded in 1991 and began exporting unrooted cuttings in 1993. Based in Tepoztlan, Morelos, just outside of Mexico City, Mexico, the operation opened with 2 hectares or 5 acres. With time and new customers, the farm has experienced rapid growth, now spanning 40 hectares or 99 acres, says Vivero’s Dennis Hitzigrath. “The first 10 years, production was doubling every season,” Hitzigrath says. “In the last three years, it’s been about 20 percent.”     The independent operation grows 100 million cuttings annually for several breeders, serving the North American market. Hitzigrath says consolidation among breeders has brought more of a focus on Vivero Internacional from third-party breeders in recent years. This growing interest is spurring even more growth. “We are planning for a minimum growth of 20 percent,” Hitzigrath says. “We are adding more production space and hope to be […]

Read More

August 19, 2015

Greenhouse Growing Recommendations For Lobularia

Modern-day Lobularias are garden classics with good vigor and long bloom times. These growing recommendations will help keep your crop in prime condition.

Read More
Mike McGroarty, owner of Mike’s Backyard Nursery

July 29, 2015

Backyard Success: Mike McGroarty Educates Aspiring Grow…

Mike’s Backyard Nursery sits on a long, narrow, 5-acre property located in Perry, Ohio. There, customers can find a variety of flowering shrubs available, all in 2-quart pots, and all for sale for $5.97 each. Owner Mike McGroarty, a lifelong resident of Perry, says the town has a lot of plant nurseries, including 100 wholesale growers within a 10-mile radius of his house. That doesn’t discourage McGroarty, because he knows that while there are a lot of nurseries in his area, no one else is doing what he is doing. McGroarty has learned about plants — and marketing them to his audience — through decades of experience. He has never hesitated to pass along his knowledge to other growers looking to start their own backyard operations, and has created an entire program to educate aspiring growers. McGroarty Likes To Practice What He Preaches McGroarty’s operation serves as the laboratory for […]

Read More
cannabis, marijuana plant

June 27, 2015

Concern Grows Over Unregulated Pesticide Use On Cannabi…

As most growers know well, the federal government regulates all insecticides, fungicides, herbicides and other commercial chemicals used on agricultural crops. Therein lies the problem with use of chemicals on cannabis crops – so far, the feds want nothing to do with legalized marijuana. According to “Concern Grows Over Unregulated Pesticide Use On Cannabis,” a June 17 article on the National Public Radio (NPR) network by Agribusiness Reporter Luke Runyon, the lack of regulated chemicals for cannabis has left growers to experiment on their own. “In the absence of any direction the subject of pesticide use on the crop has just devolved to whatever people think is working or they think is appropriate,” said Colorado State University Entomologist Whitney Cranshaw in the NPR report. “Sometimes they’ve used some things that are appropriate, sometimes unsafe.” Denver officials held tens of thousands of marijuana plants earlier this year due to safety concerns, but […]

Read More

June 16, 2015

The Butterfly Effect: Insect’s Wings Key To Azalea Poll…

A researcher from North Carolina State University (NC State) has found that in the case of the flame azalea (Rhododendron calendulaceum), all pollinators are not created equal. In fact, due to the flower’s unique reproductive structure, butterflies — and specifically, their wings — are the key to pollination. The flame azalea is commonly found in the Appalachian Mountains, ranging from as far north as New York to Georgia in the south. Like most azaleas, the flowers are large, and have an unusual structure: both the anther (male) and stigma (female) parts are very elongated and separated from one another. NC State biologist Mary Jane Epps was interested in how the azalea’s flower structure affected its pollination. “In order for a plant to reproduce, a pollinator — usually an insect — has to spread the pollen from the anther to the stigma,” Epps says. “In the case of the flame azalea, […]

Read More
Bee on a Sedum

March 17, 2015

4 Key Pollinator Research Projects To Be Funded By Hort…

The Horticultural Research Institute will grant $125,000 in financial support for four key projects as part of the Horticultural Industry Bee & Pollinator Stewardship Initiative. The Initiative has three primary goals. First, to convene a task force to develop a bee and pollinator stewardship program, including creation of best management practices for plant production. Second, to identify and fund research that will help answer key science questions and fill gaps needed to design and refine the stewardship program. Third, to seek to positively position the horticultural community and its customers by collaborating with other compatible groups interested in augmenting pollinator habitat and protection.

Read More

March 11, 2015

Pollinator Initiative Promotes Bee-Friendly Talking Poi…

AmericanHort and the Society of American Florists are working tirelessly with the ornamental industry's Pollinator Stewardship Initiative on a number of new projects.

Read More

February 11, 2015

Infusion Technology Boosts Seed Performance, Study Sugg…

Seven-year-old wheat seed germination can increase by as much as 83 percent, according to a Vital Force Technology Study that looks at the effects of energy infusion technology on plant vitality.

Read More

February 3, 2015

American Floral Endowment Accepting Research Pre-Propos…

If you are pursuing a floriculture research project, now is the time to apply for funding through the American Floral Endowment. Research pre-proposal applications for 2015-2016 funding are due to AFE by June 1, 2015.

Read More

January 27, 2015

Marijuana’s Trajectory And Ascent To Horticultural Cr…

Marijuana growing is poised for change as growers and researchers focus on improving production practices.

Read More

December 9, 2014

Greenhouse Production: Two Years Of Basics & Beyond…

Greenhouse Grower's Basics & Beyond articles cover some of the latest news and research going on in greenhouse production. Here are article links for the last two years.

Read More
GrowIt! App Wins Gold At Design100 2014 US Mobile & App Design Awards

November 24, 2014

GrowIt! App Wins Gold At Design100 2014 US Mobile &…

The social garden app GrowIt! takes the Gold Winner award at the design100 2014 Mobile & App Design Awards.

Read More

November 10, 2014

The Perennial Farm Joins HGTV HOME Plant Collection

The Perennial Farm joins the HGTV HOME Plant Collection growers' network for 2015.

Read More

November 4, 2014

AmericanHort Publishes Revised American Standard For Nu…

AmericanHort announces the revised American Standard for Nursery Stock (ANSI Z60.1) is now available for industry use. The Standard reflects the consensus of the industry regarding how nursery stock — living plants other than annuals — should be specified and sold within the trade.

Read More

September 26, 2014

Master The Art Of Watering

Watering is elemental to healthy plants, but one of the hardest concepts for new employees to master in the greenhouse. Recommend these tips to start them off right.

Read More
[gravityform id="35" title="false" description="false"]