Manage pH And Soluble Salts In Hydroponics

The pH controller (center), dilute acid tank and 8 solenoid valves with distribution lines (left) and datalogger (right)

Hydroponic greenhouse production has garnered increasing interest nationwide. For growers transitioning from greenhouse container production to hydroponics, it is important to be aware of some differences in monitoring pH and EC (electrical conductivity, a measure of soluble salts). This article discusses these differences and presents a case study in pH and EC monitoring.

Acquiring Target pH In Hydroponics Takes Practice

Many container substrate components such as peat, vermiculite, coir and wood products have a moderate buffering capacity for pH. That means it takes large changes in fertilization or acid injection to bring about a modest change in pH. For example, when we observed high pH in 4-inch bedding plants, we switched temporarily to a very acidic fertilizer (100 percent of nitrogen from ammonium/urea instead of 40 percent), it took about a week for a pH change of about 0.5 to 1.0 units to take place. In contrast, pH can change much more dramatically in hydroponic production because water and inert substrates such as perlite or rockwool have very little pH buffering. We have frequently observed pH changes of 1 to 2 units in one day.

In containerized production, it is usually recommended to monitor root-zone pH using the PourThru or 1:2 dilution method once every week or two. In hydroponics, it is critical to monitor pH at least every day. The pH may be monitored by hand — that is, sampling the nutrient solution being circulated to the roots. Alternatively, monitoring may be done continuously using an automated system. These systems vary in their level of sophistication and cost. Sensors that continuously monitor and digitally display pH and EC are on the less expensive end of the spectrum. Other systems can be connected to dataloggers or computers to record values, and high-end integrated systems that use measured values and target thresholds to adjust pH and EC are more expensive.

The target nutrient solution pH in hydroponics is similar to suggested root-zone pH in container production — about 5.5 to 6.5 depending on the crop. To ensure adequate availability of micronutrients in hydroponics, the lower side of these recommendations is often followed, such as a target pH of 5.5. When pH adjustment needs to be made, the tools to solve the problem are also essentially the same as in container production: adjusting the nitrogen form in the fertilizer or adding acid or base. Ammonium and urea are acidic forms of nitrogen, whereas nitrate will increase the pH. By adjusting the ratio of nitrogen sources in the fertilizer solution, pH can be controlled.

With respect to adding acids or bases when a large water reservoir is used, allow time for sufficient mixing. Check the resulting pH after mixing. Continue to add acid or base if further adjustment is needed. Be careful not to overshoot the mark by adding too much at first. As growers gain experience with the growing conditions, they will have a better idea as to how much to add.

High EC Can Be Problematic In Some Hydroponic Systems

The EC of the hydroponic nutrient solution is a measure of all of the salts dissolved in water, including those added in the fertilizer and those present as impurities in the water source. When the water source is relatively pure, the EC is a decent indicator of the fertilizer available to the plant. EC targets vary by crop but are often in the range of 1.0 to 2.0 mS/cm from the fertilizer plus the EC contribution from the water source. A low EC indicates that not enough fertilizer is being supplied to meet plant needs.

In closed hydroponic systems where irrigation water is captured and reused, high EC is a more common problem. This occurs when the non-fertilizer salts and any fertilizer ions supplied above plant needs remain in the nutrient solution and accumulate. Many hydroponic growers find it necessary to filter their tap water so that it is suitable for closed hydroponic systems.

Just like pH, EC should be monitored more frequently in hydroponics than in container production. Though crops vary in their salt sensitivity, a general recommendation is to avoid EC greater than 4.0 mS/cm. In open hydroponic systems where the irrigation water is not captured and reused, the buildup of salts can be managed by applying excess water to leach out soluble salts. In closed systems you will need to “bleed” the reservoir, which involves purposely draining off some fraction of the nutrient solution and replacing it with fresh water.

It is important to get a laboratory analysis of the nutrient solution every week or two to determine the actual nutrients that make up the EC. The solution may be at target EC levels, but if most of this is from non-fertilizer salts that have accumulated, such as bicarbonates, sodium and chloride, then the solution may still be low in fertility. The lab results can also be used to adjust the specific fertilizer ions to make the nutrient solution better balanced to crop needs.

Study Looks At pH And EC Control

To investigate and demonstrate the importance of pH and EC control in hydroponics, a research laboratory was designed and constructed in a greenhouse at the Ohio Agricultural Research and Development Center in Wooster, Ohio, in the spring of 2008. The laboratory consisted of 16 troughs designed to grow lettuce using the nutrient film technique (NFT). The water and nutrient delivery system was capable of randomly and simultaneously delivering different treatments to each of the growing channels using eight solution tanks. Each growing channel was 12 feet long and designed to grow 18 plants 8 inches apart. A datalogger was used to record environmental conditions and nutrient solution temperature.

To gain experience with this new laboratory, nutrient solution pH and EC targets were compared at two levels: pH targets of 5.4 or 6.0 and EC targets of 1.4 or 1.8 mS/cm. Lactuca ‘Rex Bibb’ and Lactuca ‘Green Leaf’ seeds were germinated in 1-inch-by-1-inch-by-1.5-inch grow cubes. The seedlings were transplanted to the growing channels in October 2008 and harvested four weeks later. A pH setting of 5.4 led to 24 percent higher yields than a pH of 6.0, while the main effect of setting EC at 1.4 compared to 1.8 mS/cm was nearly zero.

While extensive efforts were made to manually monitor and modify nutrient solution pH two to three times per day during this first experiment, pH readings were consistently found to be higher than either of the targets that were set for the experiment. These measurements showed that the pH of the nutrient solution was rising faster than we could manually modify it with dilute sulfuric acid on a two- to three-times-per-day basis. It often climbed 1 pH unit higher than the set points within a few hours.

Even though daily measurements showed EC control was reasonably consistent, it is likely that pH was too high, and therefore, extra nutrients that should have been accessible to the lettuce plants when the EC target was set to 1.8 were not available. We concluded that if pH was not kept on target in follow up experiments, the potential impact of high settings of EC on yield would not be realized.

Control pH To Improve Nutrient Use

These observations led to the purchase and installation of a pH control unit for all eight tanks prior to the second experiment in the spring of 2009. This control system can be set to measure and modify pH in each tank individually on a minute-by-minute basis, thus maintaining acid concentrations on target. It consists of a complex of eight panel-mounted Hanna mini pH indicators and controllers from Hanna Instruments in Woonsocket, R.I., that were connected to eight Bluelab pH probes from Bluelab Corporation Limited in New Zealand. One of these probes was installed in each solution tank by floating them on a 15-centimenter-by-15-centimeter-by-2.5-centimenter thick Styrofoam pad.

The overall average fresh weight for lettuce grown during the Fall 2008 experiment was 119 grams per head compared to 162 grams for the Spring 2009 experiment. While differences in climate may have contributed to higher yields in the spring, another possible explanation for the increase may have been more accurate pH control. Note that the impact of setting EC = 1.8 as opposed to EC = 1.4 led to a 17 percent greater yield compared to only a 5 percent advantage for a pH setting of 5.4 versus 6.0. Recall that there was little or no advantage for the setting EC = 1.8 during the first experiment when pH was not controlled successfully. Accurately controlling the pH allowed nutrients to be used more effectively throughout the growing period.

Growing hydroponically allows for more precise control of nutrient solution pH and EC than in containerized production. To optimize crop yield, however, EC and pH must be more frequently monitored as compared to container production.

Leave a Reply

4 comments on “Manage pH And Soluble Salts In Hydroponics

  1. Thanks for information. Can Ammonium and urea base nitrogen can be used in a deep culture? I use 5 gallon buckets with deep culture and my ph runs very high. tap water is at 9.4 and after nuterient it's 7.1-7.4. Can I use miracle grow to lower the ph?

More From ...
Sheridan Nurseries

September 3, 2015

Greenhouse Grower’s 2015 Operation Of The Year Sheridan Nurseries Raises The Bar

Ontario-based Sheridan Nurseries has long been an innovator in the Canadian market, but during the economic downturn, CEO Karl Stensson says the company decided to take things a step further. “We have survived the Great Depression, two World Wars and many other downturns in the economy,” he says. “During this last recession, our staff set out at being the best at what we do.” The company’s efforts have paid off. Sheridan Nurseries was named Operation of the Year at Greenhouse Grower’s Evening of Excellence, held July 13, at Cultivate’15 in Columbus, Ohio. The company was also awarded for Excellence In Perennials Production, based on its reputation for plant quality and the activities the nursery has led and been a part of, both within its company and in the industry at large. “We are elated and proud of our staff accomplishments,” says CEO Karl Stensson. “Over the last five years, we […]

Read More

September 3, 2015

Legalization Of Marijuana In California A Strong Possibility

The push for the legalization of recreational marijuana intensifies in California as proponents promote the crop’s agricultural and economical benefits.

Read More
More and more people are employing a landscape service, but that doesn’t mean they don’t still garden

September 2, 2015

Under Siege? Not Really, Just Go For A Walk

I have no trouble with people buying chocolates or wine instead of flowers to celebrate anniversaries, birthdays or peoples’ lives. We should all have choices. However, the other night I felt like I was entering the Republican caucus. I was minding my own business by the television set and became more than a little upset. A website called insteadofflowers.com came on the screen. It provided serene music and wholesome images of busy women doing busy things. It turns out that such busy women enjoy a small token of appreciation, but apparently their enjoyment, according to the voice-over, does not include flowers. This website delivers meals to the house, anything from beef brisket to beef bourguignon. It is a fine website with a good idea. But why pick on us? Why not use “insteadofbaloneysandwiches.com” or “insteadofgrilledcheeseandsoup.com,” “insteadofburgerdoodle.com,” or a dozen other things. When did flowers get to be the whipping boy? […]

Read More
Latest Stories
Sheridan Nurseries

September 3, 2015

Greenhouse Grower’s 2015 Operation Of The …

Ontario-based Sheridan Nurseries has long been an innovator in the Canadian market, but during the economic downturn, CEO Karl Stensson says the company decided to take things a step further. “We have survived the Great Depression, two World Wars and many other downturns in the economy,” he says. “During this last recession, our staff set out at being the best at what we do.” The company’s efforts have paid off. Sheridan Nurseries was named Operation of the Year at Greenhouse Grower’s Evening of Excellence, held July 13, at Cultivate’15 in Columbus, Ohio. The company was also awarded for Excellence In Perennials Production, based on its reputation for plant quality and the activities the nursery has led and been a part of, both within its company and in the industry at large. “We are elated and proud of our staff accomplishments,” says CEO Karl Stensson. “Over the last five years, we […]

Read More

September 3, 2015

Legalization Of Marijuana In California A Strong Possib…

The push for the legalization of recreational marijuana intensifies in California as proponents promote the crop’s agricultural and economical benefits.

Read More
More and more people are employing a landscape service, but that doesn’t mean they don’t still garden

September 2, 2015

Under Siege? Not Really, Just Go For A Walk

I have no trouble with people buying chocolates or wine instead of flowers to celebrate anniversaries, birthdays or peoples’ lives. We should all have choices. However, the other night I felt like I was entering the Republican caucus. I was minding my own business by the television set and became more than a little upset. A website called insteadofflowers.com came on the screen. It provided serene music and wholesome images of busy women doing busy things. It turns out that such busy women enjoy a small token of appreciation, but apparently their enjoyment, according to the voice-over, does not include flowers. This website delivers meals to the house, anything from beef brisket to beef bourguignon. It is a fine website with a good idea. But why pick on us? Why not use “insteadofbaloneysandwiches.com” or “insteadofgrilledcheeseandsoup.com,” “insteadofburgerdoodle.com,” or a dozen other things. When did flowers get to be the whipping boy? […]

Read More
Triathlon BA container shot

September 2, 2015

OHP Launches Triathlon BA, Offers Marengo SC In Smaller…

Triathlon BA biofungicide/bactericide is now available to authorized OHP distributors for shipment to states where product registration has been approved. State registration information is available here. A next generation preventive biological fungicide, bactercide Triathlon BA is labeled for use in both organic and conventional production on a wide variety of fungal and bacterial diseases on ornamentals, fruits, vegetables and herbs and spices. With the active ingredient Bacillus amyloliquefaciens, Triathlon BA provides preventive control of many foliar and soil-borne diseases such as botrytis, powdery mildew, downy mildew, rusts, leaf spots, alternaria, pythium, phytophthora, rhizoctonia, fusarium and bacterial spot. Triathlon BA, an aqueous suspension formulation, prevents establishment of disease-causing fungi and bacteria on the plant tissues. Depending on the target disease, users can foliar-apply or soil drench Triathlon BA. Repeat applications may be made at three- to 28-day intervals. Under environmental conditions that are conducive to disease development, users may apply at three- to […]

Read More

September 2, 2015

Delegation Is Key To A Successful Greenhouse Operation

In a packed room at Cultivate’15, speaker Bernie Erven presented key steps growers need to take to improve their delegation skills, the benefits of delegating and the dangers of not learning how to delegate. This is a skill, he says, that everyone needs to learn. “For all of you who are part of a family business, you are choosing not to do things the easy way,” Erven laughed, as he presented a list of ways to know whether or not you’re an effective delegator. The owner of Erven HR Services, LLC, Erven has been working with and observing family businesses for many years. In his presentation, he said, he didn’t share anything that he hasn’t seen first-hand. You might not be a good delegator if you: Tend to be a perfectionist Work more hours than anyone else Lack time to explain clearly and concisely Are often interrupted Enjoy what you used to […]

Read More
Feature image The 2015 Perennial Plant Of The Year, Geranium x cantabrigiense ‘Biokovo.’

September 1, 2015

Perennial Plant Association’s 33rd Annual Symposi…

The Perennial Plant Association's 33rd Annual Symposium, held July 27 to August 1 in Baltimore, Md., delved into the rich history of perennial suppliers and landscape architects in the Baltimore area and their influence on the perennial market today and its bright future.

Read More
Marc van Iersel

September 1, 2015

GROwing Floriculture Research And Extension

Research and outreach efforts help keep floriculture production profitable. With seemingly continuous budget cuts to university and federal budgets, it becomes increasingly difficult for them to sustain their programs and to keep making a positive impact on the industry. So what can be done to ensure that the industry will keep getting the research and outreach support it has come to rely on? There already is a variety of funding programs that support research and Extension programs in our industry. This funding is critical for many floriculture research and outreach programs. What can we do to leverage that funding and make sure it has the biggest possible impact? A program that I was part of in 2010 may serve as a model. LAUNCH was co-founded by NASA, NIKE, the U.S. Agency for International Development (USAID) and the Department of State as a program to help make innovative ideas become a […]

Read More
Greenhouse Grower’s 2015 Head Grower Of The Year Tom Wheeler - Feature image

September 1, 2015

Greenhouse Grower’s 2015 Head Grower Of Th…

Greenhouse Grower’s 2015 Head Grower Of The Year Tom Wheeler is laying a strong groundwork for the industry by mentoring future growers and instilling a sense of pride in growing quality crops.

Read More
Greenhouse Grower’s 2015 Head Grower Of The Year Tom Wheeler - Feature image

September 1, 2015

Bell Nursery USA Cultivates New Growers Through Interns…

Bell Nursery USA started its internship program two years ago with the aim of identifying and training the growers of the future. Each season, the company’s internships give interns a broad overview of the company, exposing them to everything from growing and production to distribution, retail and finances.

Read More
Growing For Futures Logo

September 1, 2015

Growing Solutions Farm Gains New Native Plant Garden

Growing Solutions Farm, a Chicago-based vocational therapeutic garden for young adults with autism, is now the home of a pollinator-friendly native plant habitat. The raised-bed native plant display was added thanks to a donation from American Beauties Native Plants and Midwest Groundcovers, who partnered to donate 220 pollinator-friendly plants. It comes on the heels of a 2014 fundraiser hosted by the National Garden Bureau, which was able to donate more than $44,000 in cash, products and supplies to the farm by the end of 2014. “Last year, during the IGC Chicago Show, I took several guests over to Growing Solutions Farm,” says Diane Blazek of National Garden Bureau. “One of those guests, Peggy Anne Montgomery, was so inspired by this project that she and American Beauties Natives worked with Midwest Groundcovers to make this donation a reality. It’s so nice that the farm now has the plants they need to […]

Read More
Fred C. Gloeckner Foundation logo

September 1, 2015

Gloeckner Foundation Elects New Directors And Board Mem…

The Fred C. Gloeckner Foundation, Inc. held its annual meeting on May 30, 2015, electing a new president, vice president and one new board member. Newly elected officers, directors and board members are: Former vice president of the foundation, Dr. Richard Craig was elected president and chair of the research committee. Craig, a professor emeritus of plant breeding and the J. Franklin Styer Professor Emeritus of horticultural botany at Pennsylvania State University, is considered a pioneer breeder in the industry. In 1990, he was inducted into the Floriculture Hall of Fame, the industry’s highest honor. Craig has spent 45 years in genetics and breeding research, and has made countless contributions to horticultural science. Dr. Paul Allen Hammer, professor emeritus of floriculture at Purdue University, was elected vice president. Hammer has served on the Gloeckner Foundation board since 2001. His expertise in greenhouse production and management, experimental design and analysis and plant […]

Read More
Bill Lewis grower manager at Delray Plants

August 31, 2015

Delray Plants Takes Preventative Approach To Pest Contr…

Trying to control pests effectively on a wide variety of crops is a major undertaking. Delray Plants in Venus, Fla., has been using biological controls as a part of its pest control program for more than 10 years. It operates 300 acres, which includes covered structures and 7 acres of outdoor field production.

Read More
Fred C. Gloeckner Foundation logo

August 31, 2015

Gloeckner Foundation Awards 15 Research Grants

The Fred C. Gloeckner Foundation recently awarded 15 grants totaling $149,776. Fred C. Gloeckner had a keen interest and firm resolve to facilitate innovation and improve practices in floriculture. It was this vision that inspired him to start The Fred C. Gloeckner Foundation, Inc. 55 years ago. Since the foundation’s inception, more than 66 institutions have been awarded grants for this purpose, and the foundation’s support of floriculture research has totaled $6,525,642. The following grants were recently awarded: $14,000 – Kansas State University, to study the effect of the entomopathogenic fungus, Beauveria bassiana and the rove beetle, Dalotia coriaria, in suppressing populations of the western flower thrips, Frankliniella occidentalis $12,264 – North Carolina State University, for expanding leaf tissue nutritional standards in bedding plants $12,000 – University of Florida, to illuminate Lilium floral fragrance $11,842 – Stephen F. Austin State University, for its herbaceous perennial species trial garden $10,000 – Iowa […]

Read More
Feature image The 2015 Perennial Plant Of The Year, Geranium x cantabrigiense ‘Biokovo.’

August 27, 2015

The Perennial Plant Association’s Regional Sympos…

The Perennial Plant Association plans to hold its Regional Symposium October 5 in Dallas, Texas, in conjunction with the All-America Selections/Home Garden Seed Association's Summer/Fall Summit held October 5 to 8.

Read More
september_grow_rodale institute

August 25, 2015

Hospitals Are Getting Into The Organic Food Business

Growers investing in the organic food movement could serve a growing new area with vegetable transplants and starts, as well as produce, as hospitals begin to prescribe healthy diets and nutrition, and even go so far as to grow their own food. As part of a new phenomenon among progressive hospitals, health professionals are beginning to realize that without health and nutrition, programs and techniques may be done in vain or worse — obsolete. As more patients seeking a healthy diet turn to nutritionists, who recommend sugar-free, alkaline diets to prevent disease and aid in recovery, hospitals recognizing this trend are taking action. St. Luke’s Hospital in Bethlehem, Pa., recently contracted with the nearby Rodale Institute to manage an organic farm, established in 2014. The hospital, part of a six-campus network, aims to provide excellent healthcare, part of which includes educating patients about the benefits of a plant-based, organic diet. […]

Read More

August 21, 2015

Proven Winners Announces Roadshow Events For 2015

Proven Winner's Roadshow Events, held across North America, provide growers and retailers with the opportunity to learn how to grow Proven Winner's newest varieties and receive information about industry trends.

Read More
Figure 1. Mustard microgreens grown under sole-source (SS) lighting using light-emitting diode (LED) arrays.

August 21, 2015

Sole-Source LED Lighting In Horticulture: Microgreens P…

In Part 2 of a four-part lighting series highlighting the multiple uses of light-emitting diodes (LEDs), researchers examine the effects of sole-source LED lighting on microgreen production to achieve the highest quality crop possible in an energy efficient manner.

Read More
Farwest2015

August 20, 2015

Farwest 2015 Offers Tours And Showcases Vegetables, Fru…

Three 2015 Farwest offsite tours, planned for Wednesday, August 26, offer a range of focus for the industry from nursery/greenhouse growing to landscape and garden retail.

Read More