Salts In Greenhouse Crops: Don’t Get Burned

Salts In Greenhouse Crops: Don't Get Burned

Greenhouse bedding plants have been traditionally grown with high quality low-salt irrigation water because plants can be damaged when salts build up in the root zone. Because water is becoming a limiting factor in several parts of the United States and across the world, it is important to understand how floriculture crops respond to poor quality (i.e. high salt, non-potable water). 

A better understanding of which plants are most sensitive to high salts can aid growers in crop selection and leaching practices. This article will describe where salts come from in greenhouse production, detection and symptoms of high salts, and how several bedding plant species responded to high salts in experiments at Cornell University.

Origins

Soluble salts are mineral nutrients and compounds that dissolve in water. In greenhouse production, they come from several sources. First, the irrigation water itself may be high salts. This may arise if the water source is located near mineral deposits, from contamination of the water source by road de-icing salts, or from the use of reclaimed municipal water.

A survey of Florida in 2005 notes that more than 230,000 acres of landscapes, golf courses and citrus orchards were being irrigated with reclaimed municipal water. A second cause of high salts comes from the substrate being used. Composts from animal manure can be particularly high in salts; potting mixes derived from these sources should be carefully monitored.

A further source of high salts comes from excess fertilizer use. When fertilizer is applied at rates much higher than the plant is using it in combination with no leaching, soluble salts can quickly build up to excessive levels. For example, in an experiment at Cornell we fertilized impatiens Super Elfin Mix with a commercial fertilizer (21-5-20) at rates of 50, 100, 200, 350 and 500 ppm nitrogen (Figure 1). When plants were sub-irrigated (i.e. no leaching) optimal growth was found with 100 to 200 ppm N. When plants were overhead watered and received 20 percent leaching daily, 200 to 350 ppm N was required for best growth. When salt concentration (as measured by PourThru EC) was greater than 3.0, plants were damaged by high salt levels. This occurred for plants receiving 500 ppm N in the overhead system and plants receiving 350 ppm N or greater in sub-irrigation.

Detection

The simplest way to detect and monitor salt levels is using a handheld electrical conductivity (EC) meter. EC is a measure of the total amount of salts in solution. EC meters rely on the property that an electrical current cannot pass through pure water, but the more dissolved salts are, the stronger the electrical current.

EC meters can be used to check salt levels of the water source, the irrigation water (to verify accuracy of fertilizer application) and to monitor root-zone salt levels. To collect a root-zone water sample, one of two methods are followed: in the 1:2 dilution method, a water sample is prepared by combining one part substrate and two parts water. The PourThru method involves adding a small amount of water to the top of a well-watered pot and measuring the leachate that comes from the bottom. For either test, a set of steps should be followed to ensure accuracy and consistency. Excellent information can be found from North Carolina State University at PourThruInfo.com.

A low root-zone EC (Table 1, scroll down) indicates that plants are receiving insufficient fertilizer (or are grown with a slow- or controlled-release fertilizer; their nutrients are not immediately soluble in water but released over time). A high root-zone EC indicates that your fertilizer rate is too high or you have high salts coming from one of the other sources mentioned already.

Symptoms

In the presence of high salts, osmotic effects are often the first symptoms that show up. That is, as root-zone salt levels rise, roots have a more difficult time extracting enough water for the plant. The osmotic or drought-stress symptoms can be subtle at first. For example, plants receiving high salts may be shorter and have smaller flowers than counterparts not exposed to high salts because there is limited water for cell expansion and elongation (Figure 3, scroll down). Plants exposed to high soluble salts may wilt even though the substrate is moist. In particular this can occur during the afternoon, when the sun is the strongest and plant water needs are the greatest. Root tips may become damaged to high salts, which provides an entry point to disease, and further limits the ability of the root system to extract enough water and nutrients.

Under a low to moderate salt stress, some plants may only show the osmotic symptoms already described. Attentive growers may notice plants are smaller than they should be but may not know the reason for this. As salt exposure continues, additional symptoms occur when plants accumulate toxic amounts of salts in their leaves. In this case, leaf tip or edge burn (marginal necrosis) are the most common symptoms. If the stress continues, the necrosis develops further inward so that entire regions of the leaf are affected.

In monocots, leaf burn usually begins on the tip of the leaf. Older leaves tend to be affected first as they have sat on the plant the longest and have had the most time to accumulate toxic amounts of salts. The symptoms described already are the response to general salt build up.

In some cases, specific ions are to blame. For example, fluoride added to municipal water sources at 1 ppm Fl can cause toxicity. Fl toxicity symptoms are leaf tip chlorosis, which develops into necrosis over time. Monocots, such as lilies and foliage plants, chlorophytum and dracaena, are particularly susceptible to fluoride damage. When substrate pH is low, iron or manganese are readily soluble and can build up to toxic levels in leaves. Symptoms include scattered bronze/chlorotic spots across lower leaves. Zonal and seed geraniums and marigolds are especially prone to iron/manganese toxicity. For this reason, their root-zone pH should be maintained at 6.0 to 6.6.

Sensitive Plants

Guidelines that allow us to classify which bedding plants are more sensitive to general high salt buildup would help growers make crop selection and management decisions based on their water supply. In order to come up with an up-to-date classification, we carried out a greenhouse experiment at Cornell to assess the impact of high salts to 14 common bedding plant species: coleus, Elatior begonia, euphorbia hybrid, French marigold, fuchsia, impatiens, pansy, petunia, salvia, snapdragon, verbena, vinca, Zinnia angustifolia and zonal geranium.

In this experiment, we artificially created high salt levels by using table salt (sodium chloride or NaCl) added to the irrigation water at five different treatment levels. This created a range of added salt levels from 0 to 1,840 ppm sodium and from 0 to 2,840 ppm chloride.

Plugs/liners of the species were transplanted into 4-inch pots containing a commercial peat-based substrate. After one week of establishment, these plants were irrigated daily with the salt treatments already described, plus a commercial fertilizer. Irrigation took place so as to cause a small fraction of water (about 5 percent) to leach at each irrigation event.

Within each treatment, five plants were randomly sampled each week to determine PourThru EC measurements. During the experiment, EC ranged from 4.0 mS/cm (control plants) to 14.5 mS/cm (highest salt treatment). EC was “normal” for control plants (based on the interpretation from Table 1), “very high” for plants receiving 460 ppm Na plus 710 ppm Cl, and “extreme” for plants receiving the three highest salt treatments.

After five weeks of salt treatments, we measured plant height and growth (dry weight). To be able to compare different species to each other we looked at salt effects based on relative plant size–that is size in comparison to untreated controls.

As might be expected, plant species respond differently to high salts. Petunia (Figure 2, scroll down), snapdragon, fuchsia and verbena were among the most tolerant species. As EC increased from 4.0 to 7.1, plant size of this group was reduced by less than 25 percent. Pansy and Zinnia angustifolia were among the most sensitive to salts. All were dead when exposed to the highest salt treatment for five weeks. Growth was reduced by about half at EC of 7.1, and leaf-edge burn symptoms were quite dramatic at this treatment. Other plants such as French marigold and vinca were somewhat tolerant of salts. At an EC of 7.1, growth was reduced by about one-third but no leaf symptoms such as edge burn were visible. This suggests a marketable but smaller crop could be produced with a “very high” EC.

Takeaways

Caution should be taken when interpreting our results. We studied growth during the transplant stage of well-established plugs/liners. Younger seedlings are often much more sensitive to high salts. Further, we looked at crops with a relatively quick finish time. The longer plants are exposed to high salts, the more likely it is that high salt damage can occur.

Leave a Reply

More From Plant Culture...
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
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
AmericanHort

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

September 16, 2014

Ball FloraPlant’s Las Limas Facility Provides Gro…

Ball FloraPlant’s Las Limas farm in Esteli, Nicaragua, is one year away from full production, but sales and quality from the two-year-old facility are right on track.

Read More
Erysimum 'Cheers' from Darwin Perennials

September 15, 2014

Darwin Perennials Takes Production Offshore In Bogota, …

With its recent purchase of a farm in Colombia, Darwin Perennials is ready to amp up supply of its perennial genetics, to provide growers with tried-and-true varieties and comprehensive production specifications.

Read More

July 23, 2014

Plan Now To Prevent Bract Edge Burn On Poinsettias

Reduce fertilizer and water, and allow your poinsettias to develop slowly during the final four weeks of production to avoid bract edge burn.

Read More

July 11, 2014

Growing Your Crops Above Their Base Temperature

Lowering temperature set points in the greenhouse may help you combat rising heating costs.

Read More

May 1, 2014

Growers Report Nutritional Problems On Geraniums

In recent weeks, several growers have contacted Michigan State University Specialists about leaf discoloration on geraniums, especially the purpling of lower leaves.

Read More

April 22, 2014

How Two Postharvest Care Products Worked On Potted Plan…

What your potted plants look like at retail translates to sales or fails. North Carolina State University researchers report on how two postharvest care products performed.

Read More
Dianthus 'Passion' from Emerald Coast Growers

March 27, 2014

Growing Dianthus Successfully

Here's some advice on transplanting and producing this classic perennial favorite.

Read More
Aquilegia canadensis

March 10, 2014

Tips For Producing Aquilegia

Advice on planting, temperature, vernalization, lighting and more on columbine from Emerald Coast Growers' head grower Josiah Raymer.

Read More