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?

Latest Stories
Dr Allan Armitage

June 25, 2016

Three Types Of Plant Consumers To Watch

There are three emerging groups of plant consumers that you should be targeting for plant sales in the future, according to Allan Armitage.

Read More
North Creek Nurseries lower trials

June 24, 2016

North Creek Nurseries Is A Finalist For 2016 Operation …

North Creek Nurseries in Landenberg, PA, is one of three finalists for Greenhouse Grower’s 2016 Operation Of The Year award and winner of the Excellence In Sustainable Production award for 2016.

Read More
Cal Poly Logo

June 24, 2016

Cal Poly Ag College Hosting Alumni Reception At Cultiva…

Alumni and friends of The Cal Poly College of Agriculture, Food and Environmental Sciences are invited to a reception that will be held Sunday, July 10.

Read More
Stocking spring plants at Petitti Garden Center FEATURE

June 23, 2016

How Growers Can Help Retailers Sell More In Spring

Fresh from a busy spring season, retailers share their wish list of things growers can do to make spring generate even more sales.

Read More
Houwelings Tomatoes

June 23, 2016

Houweling’s Tomatoes Has A New Corporate Head Grower

Arie van der Giessen, who has led the horticultural operations for many successful regional and national greenhouse operators in North America, will start his new role in September.

Read More
Vic Frey, Kurt Weiss Greenhouses Feature

June 23, 2016

Vic Frey Named A Finalist For 2016 Head Grower Of The Y…

Vic Frey, a finalist for the 2016 Head Grower of the Year and recipient of the 2016 Excellence In Production award, was always willing to trial and experiment with the latest technology. He loved the constant change in this industry, and turned every opportunity into a teaching moment.

Read More

June 21, 2016

Sign Up For The First-Ever Flower Run At Cultivate’16

When you pack your bags for Cultivate’16 in Columbus, OH, July 9-12, don’t forget your running shoes! There are still three weeks left to train for the first annual Luxflora Flower Run, which will kick off the start of Cultivate’16 on Sunday morning, July 10. The Flower Run celebrates Luxflora‘s mission to develop a visionary, influential floriculture network in which women leaders can create, inspire, and flourish. The 5k event is an opportunity for all floriculture professionals to come together to network, build relationships, and to have some healthy fun. Running is not required – this event is walker-friendly, as well. If you opt to be an observer rather than run/walk, then join your friends at the finish line to help shower the participants with flowers. Register yourself or your company’s team today, to join in on the fun. Free Flower Run tshirts will be available to participants, while supplies […]

Read More
BASF Orkestra Intrinsic

June 21, 2016

New Mode Of Action From BASF Offers Deeper Disease Cont…

When it comes to disease control, you need all the help you can get. BASF recently hosted growers, Extension personnel, and trade media to present its newest fungicide with two active ingredients, offering dual modes of action.

Read More

June 20, 2016

7 Garden Retailers Announced Closings This Month

Several established garden stores announced they were closing at the end of the 2016 season. Most of these retailers are decades old, including one that is closing after 133 years in business.

Read More

June 20, 2016

Industry’s First Plant Pricing Survey Is Open

The green industry has almost no research on plant pricing. With an industry that struggles to survive on slim margins, that's a problem. This survey is designed to help address the need, and we invite everyone to participate.

Read More
IGC 2016 Valley Forge Casino Resort

June 20, 2016

Stuff You’ll Want To Check Out At EIGC

Planning on attending the Easter Show For IGCs? Here's a list of new and interesting things you'll want to do while at the Philadelphia show.

Read More
FleuroStar Award Ceremony

June 20, 2016

Begonia Hybrid ‘Miss Malibu’ Takes Home FleuroStar Awar…

The award from Fleuroselect was announced at the Green Inspiration Event in Amsterdam.

Read More
Caryopteris 'Beyond Midnight Bluebeard'

June 20, 2016

Keep The Sales Coming With 16 New Blooming Varieties Fo…

Plants that put on a show from first frost long into fall and offer the color options consumers want for their gardens go a long way toward extending sales further into the season and can help maintain your sales momentum going strong. Check out these 16 new blooming varieties, both traditional favorites and new alternatives, for your fall crop selection.

Read More
Albert Grimm, Jefferys Greenhouses

June 19, 2016

Albert Grimm Named A Finalist For 2016 Head Grower Of T…

Grimm, winner of Greenhouse Grower's Excellence in Outreach and Leadership award, is always willing to listen, continuously learn, and improve. He is a role model and empowers his employees to strive for excellence.

Read More
'Osaka' Flowering Cabbage (Sakata Ornamentals)

June 18, 2016

Mark Your Calendar For Sakata Seed Trials In August

Sakata has set two dates for its California-based trials: Aug. 15-17 in Salinas, and Aug. 17-19 in Woodland.

Read More
Practical Software Grower Vertical

June 18, 2016

Practical Software Solutions Increases Accessibility, E…

Practical Software will demonstrate Grower Vertical, its customizable and scalable enterprise management system for the horticulture industry, at Cultivate’16 in July.

Read More
Ornamental kale field at Sunlet Nursery

June 17, 2016

Sunlet Nursery Named As Finalist For 2016 Operation Of …

Sunlet Nursery in Fallbrook, CA, is one of three finalists for Greenhouse Grower’s 2016 Operation Of The Year award and winner of the Excellence In Community Leadership award for 2016.

Read More
Priva Tomato Deleafing Robot

June 16, 2016

Priva’s Tomato Deleafing Robot Nabs Innovation Award At…

GreenTech, the Netherlands-based horticulture technology trade show, opened with an award presentation for Priva’s deleafing robot, which accurately removes leaves from tomato plants without spreading viruses.

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