Plant Growth Regulator Guidelines

PGR Guidelines

“You can completely stunt the crop to the point where it will not grow again,” says Chris Fifo, technical services advisor at Swift Greenhouses in Gilman, Iowa. “With some crops, you can excessively delay flowering if you apply too much, too early–and you’ll miss the target window for sales. Then, it ends up in the compost pile. It can be very costly.”

It’s all too easy to slip up when applying PGRs, and the price for doing so increases exponentially in a tough economic environment like the one facing growers today. A little attention to detail, however, can help growers avoid costly missteps and get the most out of their PGRs.

“The key to PGR use is consistency,” says Jason Fausey, regional field development manager for Valent Professional Products.


Consistency means ensuring the correct volumes and rates are calculated each time an application is made. It means practicing over and over again to hone application techniques. Consistency also means knowing your crops and understanding the environment in which they’re growing so the application timing is right.

“Growers are familiar enough with PGRs now to give them the respect they deserve,” says Joyce Latimer, a professor of horticulture at Virginia Tech. “We don’t have as many issues with overdoses or severely stunted plants as we used to. The biggest issue is not having uniformity in crop size.”

In the greenhouse, the goal is for all plants to be of the same height. Inconsistency in height will leave the impression that growers are sloppy and the product is inferior. But in order to achieve this desired uniformity, PGRs must be applied in such a way that coverage is consistent throughout the greenhouse.

PGR Do’s and Don’ts

Do–Ensure proper rate and volume. Calibrate equipment before application.

Don’t–Use too high a rate. It’s better to make two low-rate applications than one high-rate application.

Do–Be proactive instead of reactive when it comes to applying.

Don’t–Wait too long to make an application.

Do–Read the product label carefully for dilution ratios and other key info.

Don’t–Restrict plant size so it compromises product quality.

Do–Take notes and document actions that can be repeated season after season.

Don’t–Rely on guesswork.

Do–Practice application technique with water in non-crop areas.

Don’t–Let the process become overcomplicated. Limit the number of people involved in application and decision-making.

Do–Consult university researchers for up-to-date PGR performance data.

Don’t–Use a PGR if a crop is weak or showing signs of disease.

“If you put twice the spray volume on the plants growing in the front section compared to the plants growing in the back, you’re not going to achieve consistency,” Fausey said. “You’re going to see waviness in your crops. You need to maintain a certain, specific size if you want your entire crop to sell.”

Both Fausey and Latimer recommend practicing application techniques with water in a non-crop area. This way, the proper walking speed, rate and volume can be worked out, helping to produce a more uniform response to the actual application.

Latimer also advises growers to employ as few people as possible in the application of PGRs. The fewer people involved, the more likely crops will be uniform and consistent in appearance.

“It’s best if there is a single person or limited number of people who apply PGRs and who make the decisions about when PGRs are applied,” Latimer says.


The timing of a PGR application is critical to its success, as well. Unfortunately, as Michigan State University’s Erik Runkle says, growers tend to wait too long to apply a PGR. He recommends growers apply PGRs at the first sign of vigorous growth.

“Watch the plants, use past experience and anticipate the crop growing vigorously,” Runkle says. “Don’t wait until the bitter end to try to stop it.”

Swift Greenhouses’ Fifo echoes Runkle’s assessment: “The number one thing with PGRs is you’ve got to have the timing right. You’ve got to hit things with the PGR preventively just as the plant is beginning to stretch or the flower stalk is starting to come up. Hit them early.”

At the same time, however, Fifo cautions not to use PGRs too harshly.

“Always watch the rate; don’t overdo it,” he says. “It’s better to do things twice, a week apart with a low rate, than once at a high rate. You don’t want to stop it dead in its tracks.”

Know Your Plants & Products

Complicating matters further for growers is the sheer number of PGR products now available for use on particular types of crops.

“One thing we’ve learned over the last couple years is the value of finding the right product for the right crop,” says Matt Mohrfeld, owner and manager of Matt’s Greenhouse in Fort Madison, Iowa. “Everybody would love to say there’s one gun in your arsenal but it’s not like that anymore. There are a lot of options. There are some shotgun products out there but it’s becoming very specific.”

Mohrfeld, for example, says Sumagic PGR from Valent Professional Products is his PGR of choice on perennials. He is also high on Florel brand growth regulator. “One thing we’re using more than anything right now is Sumagic,” Mohrfeld says. “When it got labeled for (some) veggies, it gave us a whole new tool.”

While a multitude of product options exists and there is a temptation to use them all, Latimer suggests growers identify a few products they are comfortable and confident with and work with them.

“Growers should limit the number of products to those they understand and can use consistently, depending on the diversity of the plants they’re growing,” she says.

hile growers work with researchers to develop that understanding, Fifo says it’s incumbent upon growers to do their homework. For instance, Fifo knows that a crop being grown in lower light and high humidity is likely to experience excessive growth unless properly checked by a PGR. He also knows he needs to keep a close eye on that crop and try to predict when that growth will occur.

“It’s practice. It’s trial and error,” Fifo says. “You need to be informed about the crop and how it grows in the environmental conditions you have.”

Prepare To Succeed

There are a number of other ways in which growers can help set themselves up for success with regard to their PGR program. In addition to implementing a program, Fausey says it’s a good idea to take notes and document your actions from one season so you can consult them the next. This helps save valuable time and can serve as an important reminder of what worked and what didn’t.

It’s also important to make sure plants are healthy enough to endure a PGR application. “A PGR should not be used as a front-line defense for a bad crop,” Fausey says.

Before making an application, take the time to ensure the rate and volume calculations are correct. Consult the product label. Double check the math. Review notes from the previous year.

For Mohrfeld, the two most important factors in PGR use are 1) making sure the desired application rate yields good results and 2) achieving “latent coverage.”

“It’s about quality control,” Mohrfeld says. “If we need 10 parts per million and we’re putting out five parts per million, that’s probably not where we need to be.”

The more adventurous a grower gets with a PGR, Mohrfeld adds, the more important it is to nail those calculations.
“At one rate you’re giving the consumer a great product, and at another you’re hampering the consumer performance,” he says. “As growers, we have to continue to be responsible so we don’t put focus on holding plant size down at the expense of consumer performance.”

In the end, Latimer says success with PGRs comes down to incorporating them into production practices.
“PGRs need to be treated like tools–like water, fertilizer and light levels,” she says. “Each grower needs to practice with their tools and crops to determine how they’re going to work in their environmental conditions, both in terms of how they apply PGRs and how they grow their plants.

“PGR use is a combination of art and science. We (researchers) give growers the science, but they have to develop the art.”

Leave a Reply

More From Crop Inputs...
Bee Vectoring Technology Bumblebee

December 1, 2015

New Crop Protection Solution Uses Bees To Deliver Biocontrols To Flowering Crops

The new system from Bee Vectoring Technology incorporated a powdered crop protection material into the lid of commercial bumblebee hives. Bees pick up the product when they leave the hive and deposit it on every plant they visit.

Read More
Smith Gardens Marysville outdoor field production

November 30, 2015

Why Smith Gardens’ Marysville, WA, Facility Is A Great Place To Work

Labor rates in Washington State are some of the highest in the nation, making competition for labor fierce. This is why Smith Gardens in Marysville, WA, wants to strengthen its reputation as a great place to work.

Read More
Feature - Agave ‘Blue Waves’ (Rancho Tissue Technologies)

November 30, 2015

Spice Up The Garden With 12 New Succulent And Miniature Plant Varieties

New succulents and miniature plants for 2016 offer a variety of colors and foliage textures that add interest and visual appeal to any size garden — indoors or out.

Read More
Latest Stories
Bee Vectoring Technology Bumblebee

December 1, 2015

New Crop Protection Solution Uses Bees To Deliver Bioco…

The new system from Bee Vectoring Technology incorporated a powdered crop protection material into the lid of commercial bumblebee hives. Bees pick up the product when they leave the hive and deposit it on every plant they visit.

Read More
Stockosorb Crystals_with water Agriculture leaf (Evonick)

November 21, 2015

9 Sustainable Growing Media Products For Superior Green…

Manufacturers are delivering new growing media products to help growers attempt to minimize their footprint without sacrificing quality. Here are nine new products to consider for your greenhouse operation.

Read More
Suzanne Wainwright-Evans

November 16, 2015

Real-World Biocontrols Trends From The Buglady

During ,em>Greenhouse Grower's Top 100 Breakfast at Cultivate'15, Suzanne Wainwright-Evans of Buglady Consulting discussed trends in biocontrols, including what she has seen from breeders, growers and even public gardens.

Read More

October 13, 2015

Bayer CropScience And OHP To End Marketing Partnership …

The move allows Bayer to market its ornamental products directly to greenhouses and nurseries, although OHP will still service a limited line of Bayer products.

Read More
RISE 2015 Governing Board

October 13, 2015

RISE Annual Meeting Celebrates 25 Years of Industry Adv…

The annual meeting for RISE (Responsible Industry for a Sound Environment), held the last week of September in Orlando, was more than just presentations, awards and the election of new officers. It was also a celebration of 25 years as a leading advocate for the specialty pesticide and fertilizer industries.

Read More

October 9, 2015

New Biochemical Miticide Is Designed To Combat Varroa M…

EPA recently registered Potassium Salts of Hops Beta Acids (K-HBAs), which is intended to fit into a rotation program to battle resistance.

Read More

October 7, 2015

Ball FloraPlant Eliminates Neonicotinoid Use On Its Off…

Ball FloraPlant has announced its offshore cuttings farms did not use neonicotinoid-based pest management chemicals during its spring crop production last shipping season, and will continue to be neonic free this year. Instead, the company and its greenhouse managers have relied on alternative means to supply insect-free cuttings to its global customer base.

Read More
Nemasys And Millenium Beneficial Nematodes from BASFm_Nematodes

October 7, 2015

How BASF’s UK Biological Production Facility Expa…

BASF has expanded its biologicals production facility in Littlehampton, UK. The new capacity increases the company’s ability to double the production of beneficial nematodes and inoculants.

Read More

September 25, 2015

Canadian Sphagnum Peat Moss Association Announces Early…

According to an August 31 survey of members of the Canadian Sphagnum Peat Moss Association (CSPMA), whose members represent approximately 95 percent of all North American peat production, the peat harvest season has been adequate, but not strong, and could cause shortages and potentially higher transportation costs. Down To The Dirty Details The survey inquired about the status of CSPMA members’ 2015 Actual Harvest (including an estimate of what can be expected to be harvested for the remainder of the season) as a percentage of their 2015 Expected Harvest. The lack of a strong harvest overall may challenge peat availability. The Prairie Provinces (Manitoba 98 percent, Saskatchewan 88 percent and Alberta 94 percent), experienced early favorable weather conditions and a strong start to the year. This helped to minimize periodic, negative, weather-related conditions during the balance of the harvest season, and the harvest numbers are close to achieving the expected amounts. […]

Read More

September 23, 2015

New Crop Protection Products And Label Updates

Here are some of the most recent products released and label updates for crop protection agents in the greenhouse and nursery market. Fame Fungicides (FMC Corp.) FMC Corp. has introduce Fame fungicides, a family of FRAC 11 group (Strobilurin) products that delivers fast-acting, patented fluoxastrobin protection against major soil and foliar diseases. Rainfast in 15 minutes, Fame fungicides can be used on most greenhouse and nursery plants and provide fast foliar and root uptake. “Proven by university research, Fame fungicides offer fluoxastrobin action, which ensures a high degree of systemic activity to provide very rapid disease protection and stop further growth of established disease,” says Naimur Rahman, strategy and fungicide marketing product manager for FMC. The Fame fungicide family includes: • Fame SC: a suspension concentrate fungicide containing fluoxastrobin that controls major diseases, including anthracnose, downy mildew, powdery mildew, scab and leaf spot. It provides rapid foliar and root uptake […]

Read More
Offshore farm profiles Dummen Orange Las Mercedes Solanaceas GH

September 8, 2015

Dümmen Orange Implementing Consistent Standards On All …

Owning and operating several locations can be a challenge in maintaining consistent quality and cleanliness across the board. This is true of both breeders and growers. But those who do it right have invested in technology and practices that ensure that plant quality matches, no matter where their plants are shipped from. That’s the goal for Dümmen Orange. Now the world’s largest producer of unrooted cuttings, the company has a combined 150 hectares or 370 acres of production space worldwide, dedicated to cuttings production. Recent acquisitions of product portfolios, both this year and in the past few, has raised the company’s cuttings production expectation to more than 1.4 billion, including 350 million in North America. It has farms all over the world (see the 2015 Top Cuttings Producers ranking to see where), and produces cuttings for its own genetics, as well as collaborating with more than 30 third-party breeders across all […]

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
Bob’s Market and Greenhouses’ Ron Morris pours Stockosorb into the hopper for distribution on the conveyor line

August 13, 2015

How Bob’s Market And Greenhouses Improved Growing…

My father started our company 45 years ago growing bedding plants, mainly early season production and finished plants for our West Virginia market. It was in the early 1980s that we started growing earlier spring production and shipping materials to southern markets, and by the late 1980s, we also produced pansies for fall. We started using hydrogels when they first came on the market in the early 1990s and found that they really helped with our production by keeping plants healthier for these new markets. Over the years, we’ve grown to be a large young plant producer and have a sizable business growing finished plants in cell packs, 4 1/2-inch pots, 6-inch pots, gallon containers, hanging baskets, multiple sizes of large containers and large baskets for municipal use. Creating The Ideal Soil Mix With our old system, it took several workers to mix pre-made soil with slow-release fertilizers in cement […]

Read More
Fertilizer Rates Feature Image

August 12, 2015

Selecting Fertilizer Rates For Several Spring Bedding P…

Fertilizing bedding plants can be difficult due to the differing needs of the large variety of plants that we grow. Many operations do not grow enough of any one crop to cater the fertilizer specifically for each crop. Therefore, grouping crops with similar fertilizer requirements and having two to three fertilizer strengths available is a practical way to ensure plants are getting the fertilizer they need. With many new plant varieties on the market, we wanted to conduct a trial at Cornell University to determine best fertilizer rates for several common bedding plant crops. 22 Bedding Plants Studied To Establish Fertilizer Rates Plugs and rooted liners of 22 crops (Table 1) were transplanted into 4-inch (500 mL volume) round pots with a commercial peat/perlite based substrate. The plants were grown in a glass greenhouse at Cornell University during the spring season at a spacing of one plant per square foot. Heating set […]

Read More
Feature image The Aphid Guard Aphid Banker Plant, coming soon to the market, supports beneficial insect populations.

June 21, 2015

The Latest In Crop Protection

Protecting your plants from the latest threats is no easy task, but new product lines promise to safely and effectively eliminate a wide range of pests and diseases, without harming your employees or the environment.

Read More
Bee On Flower

June 18, 2015

Pest Management And Marketing Strategies For Bee-Friend…

Michigan State University Extension shares pest management practices to produce plants that are safe for pollinators and marketing strategies for clearing up confusion about bee-friendly plants.

Read More

June 13, 2015

UMASS Fertilizer Trials Recommend Nature’s Source Organ…

In a recent online fact-sheet at its Extension website, the UMass Amherst Center for Agriculture, Food and the Environment lists Nature’s Source Organic Plant Food 3-1-1 as “the best liquid organic fertilizer,” according to Dr. Douglas Cox, Stockbridge School of Agriculture. It is called-out by the Extension after a number of years of studying the use of organic fertilizers for growing commercial greenhouse crops. The trials evaluated traditional water soluble and granular slow-release chemical fertilizers. Dr. Cox recommends Nature’s Source Organic Plant Food 3-1-1 as a liquid fertilizer that is readily available, cost effective, OMRI-listed and with good label directions for greenhouses. He also mentions the ease-of-use in how it mixes well with water and can pass fertilizer injectors. “Nature’s Source is currently the best liquid organic fertilizer,” Cox wrote in his article “Organic Fertilizers – Thoughts on Using Liquid Organic Fertilizers for Greenhouse Plants,” “I have seen no foliar chlorosis yet with this fertilizer. Nature’s source is widely available and a great […]

Read More

June 10, 2015

BASF’s Sultan Miticide Receives California Regist…

BASF Sultan miticide recently received registration in California, giving ornamental growers a new rapid, targeted mode of action for mite control. Sultan miticide, with active ingredient cyflumetofen, offers ornamental growers targeted knockdown of all life stages of tetranychid mites, with long residual control. It has practically no toxicity to beneficial insects, including predatory mites and pollinators. Sultan miticide offers a new mode of action to combat cross-resistance with other commercial miticides, and is compatible with integrated pest management programs (IPM). “The long-awaited California registration of Sultan miticide is exciting news. Greenhouse, nursery and landscape professionals in the state now have a new class of chemistry that gives them fast control over all life stages of plant-damaging mite populations,” says Joe Lara, senior product manager for BASF. “Sultan miticide now provides California growers with a much needed new first choice for miticide resistance management programs that won’t disrupt populations of beneficial […]

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