When Fertilizing, Don’t Neglect The Root Zone

Controlled release series sponsors

Bedding and potted plants are traditionally fertilized daily or several times a week with water soluble fertilizer (WSF) applied in the irrigation water. With WSF, the fertilizer components are in a form that can be directly absorbed by the plant. This also means the fertilizer components can immediately impact the soluble salts and the pH of the substrate. WSF are also in a form that can readily be leached from the root zone.

When using controlled-release fertilizers (CRF) the nutrients are primarily held within the CRF prills and are not available for plant absorption until they are released slowly over time. Thus, when a CRF is added to the substrate, its effects on pH and salts are not immediate. Instead, they occur slowly over time as nutrients diffuse from the prills. Use the results from three studies to better manage the root-zone pH and electrical conductivity (EC) when using CRFs.

The Study: Poinsettias

Rooted cuttings of ‘Prestige Red’ and ‘Peterstar Red’ poinsettias were transplanted into 6-inch containers filled with a commercial soilless substrate to see how pH and EC would respond to WSF
and CRFs.

Throughout the 14-week production period, plants received either Jack’s 21-5-20 at 250 parts per million (ppm) nitrogen, a WSF, or Osmocote Plus 15-9-12 (5 to 6 month formulation) applied as a top dress at rates of 4, 6, 8 and 10 pounds per cubic yard (lbs./yd³) of substrate.  Substrate pH and EC was monitored periodically using the Pour Thru method.

To see graphs indicating the Pour Thru pH and EC of poinsettias grown with WSF or CRF, click here.

The Study: Bedding Plants

This experiment looked at the effect of CRF rates on pH, EC and nutrient leaching of Petunia ‘Fame Blue,’ Lantana ‘Landmark Citrus,’ and ‘Electric Lime’ coleus. Rooted liners were transplanted into 6-inch containers with a commercial soilless substrate. Plants were grown for six weeks and received either WSF or CRFs.

WSF was applied daily in the irrigation water at either 100 or 200 ppm N 21-5-20. Osmocote Plus 15-9-12 (3 to 4 month formulation) was applied as a top dress at rates of 2, 4, 6 and 8 lbs./yd³ of substrate, which roughly correlates to a low-label application rate up to a medium-to-high label rate. Again, substrate pH and EC was monitored periodically using the Pour Thru method.

 
The Study: Propagation

Cuttings of Impatiens ‘Celebrette Apricot’ were stuck in 105-cell propagation trays filled with soilless substrate containing no fertilizer charge or 5, 10, 20 or 40 lbs./yd3 of Osmocote Plus 15-9-12 (3 to 4 month formulation) CRF of substrate (corresponding to roughly medium or 1, 2 or 4 times the high label rates).
Cuttings were placed under a clear acidified water mist, while another set of cuttings in the above substrate mix (without CRF) were placed under mist containing 50 ppm N from a balanced feed. The plug press or plug extraction method was conducted weekly to monitor the pH and EC of the propagation liners.

Both Fertilizer Treatments Affect Root Zone EC And pH

The EC guidelines that are widely used by the greenhouse industry were developed for WSFs. Following these guidelines, a Pour Thru EC of 1.0 to 2.6 milliSiemens per centimeter (mS/cm) is desirable to supply adequate fertility for low-to-medium vigor bedding plants. For heavy feeding plants such as poinsettias, garden mums and vigorous petunias, an
EC of 2.6 to 4.6 mS/cm is desirable.

Methods for conducting each experiment are described in the sidebars on the following page. In the poinsettia experiment, the WSF treatment resulted in an EC within 3.5 to 4.5 mS/cm for most of the crop period. By the end of the experiment when plants were absorbing less nutrients, EC rose to potentially harmful levels in the WSF treatment. For CRF, the EC values were always below 2.6 mS/cm, and for the lower application rates, these were always below 1.0.

‘Peterstar Red’ poinsettias fertilized with WSF were about the same size as those receiving 6 lbs./yd³ or more CRF. Plants receiving 4 lbs./yd³ CRF were a bit smaller. For ‘Prestige Red,’ 10 lbs./yd³ was required to equal the size of liquid-fed plants, and lower amounts led to a smaller plant. The recommended substrate pH for poinsettia is between 5.5 and 6.5; this ensures that nutrients are soluble and readily available. The pH of plants irrigated with WSF was within the recommended range throughout the experiment, whereas for all CRF treatments substrate pH quickly rose above 6.5 and remained there for the rest of the experiment.

In the bedding plant experiment, petunia, a moderately heavy feeder, with 200 ppm N from WSF produced the largest plants. The other treatments, including the 100 ppm N WSF, produced markedly smaller plants. Lantana and coleus are less vigorous feeders and responded well to CRF. For these two species, 8 lbs./yd³ CRF produced plants as large as the 200 ppm N WSF treatment. Plants irrigated with 100 ppm N WSF or 6 lbs./yd³ were intermediate-sized, and lower application rates of CRF (2 or 4 pounds) led to somewhat smaller plants.

During the six-week trial, only plants irrigated with 200 ppm N WSF had a pH of 6.5 or lower. This is due to the moderately acidic nature of 21-5-20 fertilizer. Neither the 100 ppm N WSF nor any of the CRF treatments supplied enough acidic nitrogen to keep pH less than 6.5. The EC of the WSF treatments was within the 1.0 to 2.6 mS/cm range, which is optimum for most bedding plants. In contrast, the CRF treatments had nearly constant EC, which varied from 0.4-0.6 mS/cm. In terms of nutrient leaching, CRFs are superior to WSF. CRFs leached 5 to 10 times less nitrogen, phosphorus and potassium than the WSF counterparts.

In the propagation experiment, one week after sticking cuttings there was little difference in both substrate pH and EC across our different fertilizer treatments. As time in propagation passed, the fertilizers had a greater impact on both pH and EC. Both CRF and WSF decreased pH and increased EC, although the amount of CRF incorporated affected the degree of influence. By mixing the CRF into the propagation substrate the day before sticking cuttings, the effect of CRF incorporation was negligible at first and increased over time. The release pattern of nutrients from CRF prills corresponds well to adventitious root development in cuttings, with a greater demand for nutrients as roots develop. This suggests that CRFs may be a valuable tool for cutting propagation.

Monitor EC And pH Regularly To Ensure Success

In our trials we found that EC guidelines for WSF cannot be directly extended to CRF. Because CRFs are slow-release fertilizer sources, the EC values we measured were much lower as compared to WSF. For CRF, however, a low EC does not necessarily indicate that the fertility level is insufficient for optimum plant growth. For example, the growth of ‘Peterstar Red’ poinsettia receiving 6 lbs./yd³ CRF was similar to plants receiving 250 ppm N WSF. Yet, Pour Thru EC averaged 0.8 for CRF and 4.2 for WSF.

Monitoring EC is still important when using CRF. A stable EC indicates that nutrient release is in sync with plant needs. Excessively high EC, greater than 4.5 mS/cm, indicates that fertilizer salts are building up in the substrate and this can lead to plant damage from salt burn. Symptoms include death of root tips (which can provide an entry point to root diseases), wilting due to the inability to absorb enough water and browning of lower leaf edges as salts build up to harmful levels in the leaves.

With CRFs, a high EC may indicate that fertilizer release is greater than the plant needs, although this is not common. More commonly, high EC is found when hot growing temperatures cause a rapid release of nutrients from the fertilizer prill.

A high EC can also occur when CRF is incorporated into a substrate and held for a long time (more than two to four weeks) before transplanting, which leads to a release of fertilizer salts before the substrate is used. These cases illustrate the need to periodically measure EC when using CRF, especially during hot temperatures. Regardless of the cause of high EC, the remedy is the same — drench the substrate thoroughly with clear water to leach out excess salts. Monitor EC and repeat leaching as necessary.

Growers should also periodically measure pH when using CRFs. CRFs were more likely to result in plants with a high substrate pH than a moderately acidic WSF (21-5-20). When switching to CRFs, growers may find they need to be more proactive with pH control. To lower pH, sulfuric, phosphoric or nitric acids can be added to acidify the irrigation water or use periodic drenches with an acidic WSF (such as 21-7-7). More information on monitoring and adjusting root-zone pH is available at Greenhouse.cornell.edu and Flowers.hort.purdue.edu

CRFs can be a great tool to have in your fertilizer tool kit to reduce runoff of nutrients into the environment or to reduce the labor associated with mixing and applying WSF. Just don’t lose sight of the details. Continue to monitor pH and EC and adjust growing practices when necessary to keep these in check.

Leave a Reply

More From Fertilization...
Lavandula 'Meerlo' (Sunset Western Garden Collection)

March 3, 2015

Why You Will Still Grow Today’s Big Perennial 10 Years From Now

What will be the next big perennial? Breeders say it takes more than a splashy plant to distinguish itself in the market. Therefore, the question is not what will be the next big perennial, but rather what perennial performs well enough in the garden to have staying power in the market for years to come.

Read More

March 2, 2015

Avoid Surprises On The Delivery Dock

A call in advance about problems with a plant shipment to a retailer you supply goes a long way toward customer satisfaction.

Read More
Janeen Wright

March 2, 2015

Deliver Plant Quality That Trumps Price [Opinion]

The industry's goal is to have loyal customers who return to the same plants time and time again, not because of price, but owing to a plant brand that shouts top-notch garden performance and is synonymous with excellence, which gives them the secure knowledge that their investment will be worth every hard-earned cent.

Read More
Latest Stories

January 9, 2015

6 New Fertilizer Products For Healthy Plants

These five products add even more options for delivering nutrients to the root zone.

Read More

January 7, 2015

Fertilizers And The Future

As growers look for new ways to cut costs and conserve resources, fertilizer and equipment companies are offering products that strive to save water, reduce toxic runoff and keep chemicals out of the equation.

Read More

December 31, 2014

Gain Greater Control Of Fertilizer With Automated Ferti…

University researchers look at integrating irrigation and fertilization with the help of water sensors to reduce fertilizer treatments and improve application timing.

Read More

October 30, 2014

Basics & Beyond: Comparing Substrate Fertilizer Ame…

Cornell University researcher determines if substrate-incorporated slow-release fertilizers can be used to replace or reduce the need for liquid fertilizer for four spring crops.

Read More

July 24, 2014

Using Controlled Release Fertilizers To Produce Garden …

Researchers determined whether or not garden mums can be grown with controlled-release fertilizer, and if it reduces fertilizer leaching, as compared with water-soluble fertilizers.

Read More

March 14, 2014

New Foliage Pro Fertilizer Offers Complete Nutrition Pl…

Dyna-Gro Nutrition Solutions has developed a process it says is capable of keeping all 16 essential plant nutrients in solution form.

Read More

January 30, 2014

OASIS Grower Solutions Introduces New One-Bag Hydroponi…

The new 16-4-17 Hydroponic Fertilizer from OASIS Grower Solutions (OGS) is a one-bag solution that replaces two-part systems traditionally used by commercial hydroponic growers. It is specifically formulated for commercial hydroponic production of lettuce, herbs and vegetables.

Read More

December 30, 2013

Fertilizer Changes Growing Mix pH

When considering a fertilizer's influence on media pH, you need to know its acid or basic reaction.

Read More

December 30, 2013

Basics & Beyond: Fundamentals Of Phosphorus Nutriti…

Phosphorus is an essential element, after all.

Read More
Everris Liquid S.T.E.M.

December 30, 2013

New Fertilizers For 2014

New fertilizer products not only deliver optimum nutrition, they also provide for easier application and increased efficiency. Check out these new products to help your operation produce a healthy crop in 2014. Click through on the pages below.

Read More

December 18, 2013

Focus On Fertilizer: Micronutrients And Organics

New fertilizer products are focusing on micronutrients and providing efficient options for organic production.

Read More

August 27, 2013

BioWorks Adds EcoVita To The Verdanta Family Of Biofert…

EcoVita, a homogeneous granular organic fertilizer, has been added to Bioworks Inc.’s Verdanta biofertilizers product family. This fertilizer will be manufactured and supplied to BioWorks by DCM Corporation of Belgium, a producer of natural and organic-based fertilizers in Western Europe. EcoVita is suitable for a wide variety of crops with its gentle release curve including:• Organic fertilization as a base nutrition in potting mixes• Leafy vegetables• Fruiting vegetables (s a top dressing) • Roses and other ornamentals The new fertilizer offers long-lasting and continuous action for 75 to 100 days and contains organic phosphorus (5 percent P2O5) for fast rooting. Nutrients in EcoVita are gradually released by the soil microbes, in addition to producing humus for better rooting and less leaching. EcoVita is OMRI Listed, making it suitable for use in organic production. “We’re pleased to introduce EcoVita 7-5-10 as our organic NPK product to complement our organic products: K-Vita 2-0-20 […]

Read More

April 29, 2013

Rockwell Farms Introduces Ready-To-Pour Container Ferti…

Rockwell Farms has introduced Rockwell Farms Plant Food, a bottled liquid fertilizer that does not need to be diluted before use. Always looking for ways to help the consumer succeeed, Jason Roseman of Rockwell Farms says the operation is also always looking for ways to get consumers to come back and buy more plants and flowers. “We feel like fertilization is one of those things that can be very confusing,” Roseman says. “Not everyone does it, and not everyone knows what they’re supposed to do.” The solution: Rockwell Farms Plant Food. The formulation is 150 ppm of a 20-10-20 fertilizer and is sold in 24-ounce bottles. Rockwell recommends that one bottle be used to fertilize 1.5- to 3-gallon outdoor plant and flower containers every 21 days. The product’s signage shows a young patio gardener pouring the bottled fertilizer on a windowbox with the tagline, “Just pour on your way out […]

Read More

April 29, 2013

Plant Products To Be Purchased By MGS Horticultural And…

MGS Horticultural Inc., a full-service supplier of fertilizers, pest control products, seeds and substrates in North America, together with Haifa Chemicals, a global supplier of potassium nitrate for agriculture and industry, specialty plant nutrients and food phosphates, today announced a plan to purchase Canadian fertilizer and pesticides supplier Plant Products Co. Ltd. The deal is anticipated to close by the end of June 2013. MGS will acquire Plant Products’ Canadian distribution business, sales force and name. MGS plans to use both names (MGS Horticultural and Plant Products) in all communications going forward. MGS will maintain locations in Leamington, ON; Brampton, ON; Laval, QC; St. Hyacinthe, QC; and Detroit, Mich. As part of the deal, MGS has signed multi-year agreements with Haifa to maintain exclusive distribution of Plant-Prod Soluble Fertilizers, Acer Controlled Release Fertilizer, Stim-Root and potting soil premix fertilizers for distribution in Saskatchewan, Manitoba and Eastern Canada. “MGS is excited […]

Read More

March 19, 2013

Irrigation And Fertilizer Tips For New Vegetable Grower…

Compared to other variable costs, fertilizers are not the largest part of the budget in conventional greenhouse production. Nevertheless, over the course of the season, mistakes in fertilizer use can lead to significant damages or crop losses. That makes this an important topic for ornamental growers who are experimenting with growing vegetable crops. This article will emphasize major differences between fertilizers used in vegetable production and in ornamentals production. The different nutrition strategies, monitoring and water volume per plant will also be explained. Fertilizer In ornamental production, nutrients are delivered using various water-soluble fertilizers through a fertilizer injector, through the use of controlled-release fertilizers, or a combination of the two. There are numerous fertilizer mixes available with all the needed nutrients already included. The fertilization rate is often given in parts per million (ppm) of nitrogen (N), which is a way of expressing the fertilizer concentration. At younger stages, plants will […]

Read More

March 11, 2013

Daniels Plant Food Rebranded As Nature’s Source

Ball DPF has announced the launch of Nature’s Source, a rebranding in name and packaging for its seed extract-based plant fertilizer product Daniels Plant Food. The new brand will make its industry debut at California Spring Trials. “While we are proud of our heritage, we made this bold decision because we’re expanding sales to our existing market segments and entering new ones. It was a good opportunity to start with a fresh name and a modern look for all our products and packaging,” says Chance Finch, general manager for Ball DPF. “We wanted to make it obvious, beginning with our Nature’s Source brand name, to know our products are sourced from nature. Growers, contractors and gardeners can be confident that our effective and unique formulations remain unchanged. We’re excited about launching updated packaging for all our products, and especially the new ready-to-spray plant food for home gardeners.” The Nature’s Source brand […]

Read More

March 6, 2013

Everris Introduces E-Max Release Technology Coating Che…

Everris has introduced its new E-Max Release Technology, a proprietary coating chemistry for use on a wide variety of nutrient components that are incorporated into controlled-release fertilizer products. According to Chris Buchheit, marketing manager for Everris’ ornamental horticulture products, E-Max will help Osmocote and the company’s other existing brands deliver even better performance and value. “This coating will aid in the development of products that both complement and enhance our Osmocote portfolio and other fertilizer lines. It will increase Everris’ flexibility to create customized nutrition programs designed for horticulture growers,” Buchheit says. E-Max Release Technology is a durable, cutting-edge, reacted polymer coating for use on a variety of essential macro- and micronutrients. Nutrients coated with E-Max Technology are produced to the same performance standards as Osmocote. It will allow for continued expansion of the Everris portfolio, the ability to further enhance nutritional values and an efficient use of a grower’s […]

Read More

February 4, 2013

BioSafe Systems And Daniels Plant Food Company Will Par…

BioSafe Systems has entered into a strategic partnership with Daniels Plant Food Company, a wholly owned subsidiary of Ball Horticulture Inc. BioSafe and Daniels have worked closely together for the past two years and will now look to further develop liquid plant food serving both the conventional and organic markets. In conjunction, BioSafe Systems will be introducing its own branded line of plant food products focusing on turf, landscape and agricultural markets. “Liquid plant food is a natural progression for our company” says Rob Larose, CEO of BioSafe Systems. “It fits perfectly into our current line of green and sustainable products, and we are excited about partnering with Daniels.” Daniels manufactures and markets both conventional and organic liquid fertilizers, using botanical extracts to provide high-value nutrition to plants. BioSafe Systems develops and markets effective and sustainable products to a wide variety of industries, including fruit and vegetable production, turf and […]

Read More