January 2026 Plant Trials, Production, Research

Substrate drenches for CEA crops By W. Garrett Owen

Collate 2L (21.7% ethephon) from Fine Americas is now labeled for substrate drench application, giving U.S. greenhouse growers a new option for precise plant growth regulation. This added precision can reduce labor inputs by minimizing the need for repeated manual growth-control tasks. 

Research from The Ohio State University shows how Collate 2L drenches can help manage height and branching in annual bedding plants and herbaceous perennials, expanding the tools available for today’s floriculture operations.

Using Collate 2L as a substrate drench does not replace traditional foliar sprays or manual pinching. Instead, it complements existing practices, allowing growers to fine- tune growth and plant form. Substrate drenches allow ethephon to be absorbed by roots, move upward through the xylem and release ethylene throughout the plant, which can produce more uniform and longer lasting growth effects across crops and container sizes. Collate 2L is currently the only ethephon product approved by the EPA for substrate drench use in ornamental crop production.

Over the past several years, the Owen Lab at Ohio State University has evaluated Collate 2L drenches on annual bedding plants and herbaceous perennials. Those projects, combined with earlier research, now provide practical guidelines for using Collate 2L drenches in production. When rates are selected carefully and applications are made with attention to solution pH, drench timing, substrate and species sensitivity, Collate 2L drenches can effectively manage growth and branching, helping growers achieve target plant size with fewer corrective interventions and therefore lower labor time. 

HOW COLLATE 2L DRENCHES WORK 

Once applied to the substrate, ethephon is absorbed primarily by the roots and transported upward in the xylem. Inside the plant, ethephon breaks down and releases ethylene, which suppresses stem elongation, encourages lateral branching and can influence flowering depending on the crop and timing. Because drench solutions are absorbed through the root system and vascular tissue, they affect both roots and shoots. Trials show that shoot and root dry weight declined together as rates increased, confirming that drenches limit overall biomass, not just stem length above the pot rim. 

OHIO STATE UNIVERSITY RESEARCH 

Young plants were transplanted into peat-based substrates in 4- to 6-inch or trade-gallon containers, allowed to establish for 10 days and then drenched with Collate 2L solutions. Typical drench volumes were 3 fl oz per 4- to 5-inch pot and 5 to 10 fl oz for larger containers, applied to moist but not saturated substrate. We evaluated 20 annual bedding plant taxa at 0 (control), 25, 50, 75, 100 or 200 ppm Collate 2L and 17 herbaceous perennials at 0, 125, 250, 500, 750 or 1000 ppm Collate 2L. 

ANNUAL BEDDING PLANTS 

Across 20 annual bedding plant taxa, Collate 2L drenches of 25 to 100 ppm consistently reduce plant height and diameter in many crops and can provide commercially useful control while maintaining overall plant quality. In general, higher drench concentrations produced stronger growth regulation, but the most practical range for many annuals was 25 to 100 ppm Collate 2L, where plants remained compact, well-branched and marketable. 

Dahlia is a good example of this response. Collate 2L drenches provided strong growth control in both ‘Grandalia Dark Red’ and ‘Dahlegria Red’ without compromising visual appeal. For ‘Grandalia Dark Red’, drenches between 25 to 75 ppm Collate 2L controlled plant height and diameter without a delay in flowering (Fig. 1), creating a compact, well-filled pot. For ‘Dahlegria Red’, higher rates between 75 to 200 ppm Collate 2L were needed to achieve similar control of height and diameter. In both cultivars, drenched plants were more compact and easier to handle, yet still filled the container and presented a full, marketable plant. This improved manageability translates to time savings during production and shipping preparation. 

Geraniums (Fig. 2) also responded well to Collate 2L drenches, although the optimal range depended on type. Interspecific geranium ‘Calliope Large Dark Red’ showed effective height control at 25 to 100 ppm Collate 2L, while 200 ppm resulted in noticeable delays in flowering. Ivy geranium ‘Cascade Dark Red’ responded best with 50 to 100 ppm Collate 2L. Zonal geranium ‘Americana Dark Red’ tolerated a wider rate range of 50 to 200 ppm Collate 2L, where height and diameter were controlled without obvious delays in flowering across the rates tested. In practice, this means growers can use low to moderate rates roughly 25 to 100 ppm Collate 2L, fo most geranium programs and reserve the upper part of the range, 100 to 200 ppm Collate 2L, for vigorous zonal geranium cultivars. 

While most annual bedding plants responded well to Collate 2L drench, a handful of taxa showed limited or no change in height. This reinforces the need for small in-house trials to determine which annuals respond strongly to Collate 2L drenches and which do not.

HERBACEOUS PERENNIALS 

Across 17 flowering herbaceous perennial taxa, drenches of 125 to 500 ppm Collate 2L consistently provided growth control while maintaining overall plant quality. In general, higher drench concentrations produced stronger growth regulation, but the most practical range for many perennials was 125 to 500 ppm Collate 2L, where plants remained compact, well-branched and considered marketable. This level of control can streamline production, decrease labor for plant spacing and maintenance, and help sustain uniformity across a crop.

Perennials such as ‘Leading Lady Iron’ coreopsis (Fig. 3) and ‘Pink Mist’ scabiosa (Fig. 4) are good examples of this response. In coreopsis, drenches between 125 to 500 ppm Collate 2L produced plants that were shorter and compact. In scabiosa, similar rates controlled plant size. Beyond these crops, other herbaceous perennials such as blanket flower, foxglove, gaura Russian sage and sedum generally became shorter and more compact as drench rates increased. At rates above 500 ppm Collate 2L, several taxa such as erysimum and lamium began to show phytotoxicity, delayed flowering and especially death at 750 to 1000 ppm. Together, these results suggest that 125 to 500 ppm Collate 2L is an appropriate starting range for most herbaceous perennials, with higher rates used cautiously and only after small in-house trials to determine how individual species and cultivars respond. 

KEYS TO SUCCESSFUL COLLATE 2L DRENCHES 

The success of a Collate 2L drench program depends on more than choosing a rate. Solution pH, substrate pH and composition, and application timing all influence ethephon efficacy. To get the most out of your Collate 2L drenches, growers should: 

• Check water pH and alkalinity before mixing drench solution. Neutralize alkalinity in solution before mixing by using acid or a water conditioner. 
• Target a drench solution pH of 4.5 to 5.0. 
• Apply 7 to 14 days after transplanting and once roots are established. 
• Apply drenches to actively growing, well-watered plants. 
• Maintain substrate pH in the recommended range of 5.5 to 6.5. 

As with any PGR, species and even cultivars within a crop differ in sensitivity, so small in-house trials are essential. A practical approach is to treat a strip across the bench or a few pots per cultivar at two or three rates and compare them directly with untreated controls, paying attention to height, diameter, branching, flowering and any signs of stress. Conducting these small trials can prevent costly misapplications and reduce labor tied to correcting unintended growth responses. 

HOW COLLATE 2L DRENCHES HELP REDUCE LABOR AND PRODUCTION COSTS 

Collate 2L substrate drenches offer growers a more efficient way to manage plant height, branching and uniformity, helping reduce the time and labor typically required for manual growth-control tasks. Since drenches deliver longer-lasting, predictable regulation, growers may need fewer foliar applications, less pinching and fewer corrective adjustments during production. More compact, consistently shaped plants also streamline bench spacing, handling and shipping preparation. By reducing reactive labor and minimizing repeated interventions, Collate 2L drenches can contribute to meaningful labor and cost savings across both annual and perennial crops. 

START SMALL AND BUILD A PROGRAM 

For greenhouse owners and growers who are curious about Collate 2L drenches but hesitant to change a working PGR program, the safest path is to think of Collate 2L drenches as an additional tool. Start by identifying a few crops where extra branching, tighter canopies or reduced reliance on other PGR drenches would be valuable and test Collate 2L on a limited scale. 

Applied at appropriate rates to healthy, actively growing plants, Collate 2L drenches can produce compact, well-branched annuals and perennials that can be handled and shipped more easily. These handling and shipping advantages directly translate to labor efficiencies and reduced operational costs. As the only ethephon product currently labeled for substrate drenches in floriculture crops, Collate 2L gives growers a fresh way to fine tune crop growth and quality alongside the foliar sprays, pinching and other PGRs they already know.