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 ...
protecting bees and pollinators video

March 31, 2015

New Video On Protecting Bees And Pollinators Educates Horticulture Industry Professionals

A new educational video that provides information on the horticultural industry’s essential role in bee and pollinator stewardship is one result of industry collaboration by the Horticultural Research Institute, AmericanHort, Society of American Florists and the American Floral Endowment. “Protecting Bees & Pollinators: What Horticulture Needs to Know,” narrates the current state of bee and pollinator health, provides information on factors that impact pollinators and the environment and underscores the beneficial role horticulture plays in providing healthy pollinator ecosystems.

Read More
Basil_Persian-AAS2015_620x329

March 31, 2015

California Summer Vegetable Trials To Be Hosted By National Garden Bureau Members

Vegetable breeding companies will come together this August to host the Summer Vegetable Trials in California. Like the long-standing California Spring Trials that are held annually in California, attendees will have the opportunity to visit breeding companies' trial sites in seven locations throughout the state, from August 20-21, 2015. National Garden Bureau (NGB), the non-profit organization promoting gardening on behalf of the horticulture industry, is organizing and publicizing this event on behalf of its members.

Read More
DNA-logo

March 31, 2015

DNA Green Group Will Acquire Rijnplant

DNA Green Group and Riknplant have finalized DNA Green Group's acquisition of Rijnplant, meaning that the breeding and propagation activities in pot and cut anthurium, bougainvillea and heliconia will transfer to DNA Green Group.

Read More
Latest Stories
protecting bees and pollinators video

March 31, 2015

New Video On Protecting Bees And Pollinators Educates H…

A new educational video that provides information on the horticultural industry’s essential role in bee and pollinator stewardship is one result of industry collaboration by the Horticultural Research Institute, AmericanHort, Society of American Florists and the American Floral Endowment. “Protecting Bees & Pollinators: What Horticulture Needs to Know,” narrates the current state of bee and pollinator health, provides information on factors that impact pollinators and the environment and underscores the beneficial role horticulture plays in providing healthy pollinator ecosystems.

Read More
Basil_Persian-AAS2015_620x329

March 31, 2015

California Summer Vegetable Trials To Be Hosted By Nati…

Vegetable breeding companies will come together this August to host the Summer Vegetable Trials in California. Like the long-standing California Spring Trials that are held annually in California, attendees will have the opportunity to visit breeding companies' trial sites in seven locations throughout the state, from August 20-21, 2015. National Garden Bureau (NGB), the non-profit organization promoting gardening on behalf of the horticulture industry, is organizing and publicizing this event on behalf of its members.

Read More
DNA-logo

March 31, 2015

DNA Green Group Will Acquire Rijnplant

DNA Green Group and Riknplant have finalized DNA Green Group's acquisition of Rijnplant, meaning that the breeding and propagation activities in pot and cut anthurium, bougainvillea and heliconia will transfer to DNA Green Group.

Read More

March 31, 2015

Manufacturers Are Taking Biologicals To The Next Level

Through acquisitions and new products, many crop protection companies are making firm commitments to the future of the biocontrols industry.

Read More
Aquaponics At Brogue Hydroponics

March 30, 2015

10 Things You Need To Know About Aquaponics

Are you curious about expanding into aquaponics? From pest control to equipment, Bob and Jesse Kilgore of Brogue Hydroponics offer 10 factors you need to consider.

Read More
Aquaponics At Brogue Hydroponics

March 30, 2015

Aquaponics Is Making A Splash At Brogue Hydroponics

The owners of Brogue Hydroponics explain why they expanded into aquaponics, and how the shift has helped them uncover a new market opportunity.

Read More
Hendriks-Half-Open-Roof_GGS

March 26, 2015

10 Greenhouse Products For First-Rate Growing Environme…

From coverings to fork-lifts, greenhouse suppliers offer a variety of products to make growing easier. Check out the slideshow to learn more about these, plus several other products that can offer you value, versatility and durability.

Read More
Rose rosette on Knockout rose, April 2012. Photo credit: Alan Windham, University of Tennessee

March 25, 2015

$58 Million In APHIS Farm Bill Funding Will Support Hor…

Nearly $58 million as been allocated by the USDA's Animal and Plant Health Inspection Service (APHIS) to support the industry's Plant Pest and Disease Management and Disaster Prevention Program, under Farm Bill Section 10007. The program will support mitigation efforts for specialty crops, including providing research and other funding to address plant pest and disease priorities for the specialty crop industry, including floriculture and nursery crops.

Read More
AFE scholarship_Ryan Dickson

March 25, 2015

AFE Educational Grant And Scholarship Application Deadl…

Apply now for American Floral Endowment (AFE) scholarships or educational grants. Applications can be found online. For educational grants for 2015-2016, applications must be submitted no later than June 1. Scholarship applications are due May 1. AFE will award $40,000 in scholarships for 2015.

Read More

March 25, 2015

13 New Shrubs You’ll Find At The 2015 California …

Woody ornamentals serve as the foundation of many great landscapes, but beyond their traditional uses, shrubs also add color, structure, texture and interest to small gardens and even containers. Check out this slideshow to see some of the newest introductions you’ll get to see at this year’s California Spring Trials.

Read More

March 25, 2015

NASS Reports U.S. Honey Production Was Up By 19 Percent…

Honey production in 2014 from producers with five or more colonies totaled 178 million pounds, up 19 percent from 2013, according to a March 20 report from the USDA's National Agricultural Statistics Service (NASS).

Read More
Bloomtown_Screen Shot 2015-03-10

March 24, 2015

Bloomtown Exposes Consumers To The World Of Horticultur…

A new web series called Bloomtown is all about the mud, sweat and tears of horticulture. Filmed in St. Louis, Mo., it chronicles the world of horticulture using local flower growers, greenhouses, wholesalers, florists, consumers, retail shops and arborists, with the goal of opening consumers’ eyes to the world of horticulture around them.

Read More
OxiPhos_BioSafe2

March 23, 2015

BioSafe Makes Label Changes To OxiPhos And ZeroTol 2.0

There have been some recent label changes made to the BioSafe Systems product OxiPhos, a systemic bactericide/fungicide that reduces downy mildew spores when tank mixed with ZeroTol 2.0.

Read More

March 23, 2015

UF/IFAS Appoints Joseph Albano As Director Of Mid-Flori…

The University of Florida's Institute of Food and Agricultural Sciences (UF/IFAS) has a new directors for its Mid-Florida Research and Education Center (REC) on Apopka, Fla. The role has been filled by Joseph Albano, a research horticulturist from the U.S. Department of Agriculture with more than 25 years of experience.

Read More
Nufarm_logo

March 23, 2015

Nufarm Fungicides Now Registered For Use On Edible Crop…

Nufarm Americas announced label expansions for two of its fungicides that will provide more pest management options for the ornamental industry. The Cleary 3336 F and EG fungicides are now registered for use across a wider range of edible crops, including select greenhouse vegetables and transplants, herbs and backyard fruit.

Read More

March 23, 2015

Update To Armitage’s Greatest Perennials & Annuals …

A new update to the Greatest Perennials & Annuals app narrows the gap between consumers and grower-retailers, while providing more of Armitage’s top picks and growing advice for success with plants.

Read More
Plantbid website screenshot

March 20, 2015

Plantbid Brings Open Sourcing To Greenhouse Growers

Plantbid bridges the gap between buyers and sellers for sales and marketing networking on their own terms. The web-based, plant-sourcing platform aims to save growers time and make the business of buying and selling plants more efficient.

Read More
National Floriculture Forum 2015 029

March 18, 2015

2015 National Floriculture Forum Focuses On Marketing I…

The 2015 National Floriculture Forum, held March 6 to 7 in Minneapolis, Minn., zeroed in on the topic of marketing in horticulture and included visits to Gertens Greenhouses and Garden Center, Bailey Nurseries, Bachman’s Floral, Home and Garden and Tangletown Gardens. The annual meeting allows greenhouse and floriculture faculty, graduate students and industry partners to meet and share updates on current research, issues and initiatives.

Read More