It’s Poinsettia time! If you grow this crop, you know that meeting the height specifications can always be a challenge. The desired height requirements are as much about quality of poinsettias as they are about rack spacing and shipping capacity. In contrast, spring crops are not generally required to meet such specific height requirements, yet stem length can have a profound effect on the aesthetics, quality, performance, and of course ease of shipping. This insider article will highlight “micro-drenching” as a flexible solution to manage plant height in a variety of crops, including poinsettias.
Plant growth regulators (PGRs) that can be drenched to control height include Uniconazole, the active ingredient in Sumagic and Concise, Flurprimidol in Topflor, and Paclobutrazol found in Bonzi, Piccolo, Pac O, and Paclo Pro. Of these three active ingredients, Paclobutrazol is inexpensive, less subject to overdosing and stunting, and is the most researched PGR for micro-drench applications (Figure 1).
Figure 1: Lopez, Roberto “What’s All the Hype on Poinsettia Micro-drenches?” GrowerTalks, May 2021, pg. 52-54.
A wide variety of crops are traditionally treated with drenches of Paclobutrazol once or twice near the crop finish date to slow or stop growth for a time. This is a common ‘holding strategy’. This application can put a hard stop on plant growth which may take some time to wear off after the plant is purchased by the consumer. Micro-drenches are done earlier and more often, even weekly, at lower concentrations. The micro-drench method is a soft touch on the brake and not a full stop. Micro-drenches allow flexible control of height for the grower, while still assuring a plant’s ability to grow out for the end consumer. Typical rates used are from 0.10 ppm up to 1.0 ppm for common crops.
For Poinsettias, the considerations are somewhat different as continued growth on the consumer end is not a factor. However, final flower or bract size is a priority along with final height. Bract size of poinsettia can be negatively impacted by any growth retardants applied during the initiation and bract development periods. Therefore, the effect on bracts is a major consideration when choosing a method of height control. The Paclobutrazol micro-drench method has the least influence on bract size when compared to other PGR application options.
Applications to poinsettia can begin once new shoots have elongated after the pinch, generally from late September to early October, and can continue until finish. Graphical tracking of poinsettia height is used to make weekly decisions to apply a micro-drench or not. For vigorous and moderately vigorous varieties, GGSPro recommends rates from 0.10 to 0.125 ppm for growers in the Northern US, and 0.10 to 0.20 ppm for Southern growers. Note, some genetics are compact and naturally low vigorous depending on your location and may not require PGR applications. The reduced PGR dose and optional weekly application frequency of micro-drenching provides the most flexible height control technique. A minimum amount of Paclobutrazol is used and minimal reduction on poinsettia bracts is attained compared to a full drench of 0.5 to 1.0 ppm after October 25th, which can cause a 10-15% reduction in bract size.
For Spring Crops, micro-drenches can begin as soon as the transplant has roots to the edge of the pot and can be carried out throughout the production period, as needed for amenable crops. The goal for these crops is to prevent the need for a full drench late in production, avoiding any negative effect on customer satisfaction.
Table 1 lists guidelines from trials carried out by Dr. Roberto Lopez’s lab at Michigan State University on some common crops. GGSPro recommends starting at the low end of the range when trialing PGRs and designating an un-treated control plant or pack for comparison.
Table 1: Paclobutrazol Micro-Drench Guidelines for Common Crops.1
1Lopez, Roberto G. “Do Micro Drenches on Annuals and Perennials Work?” Greenhouse Grower, May 2021, pg. 16-18.
The concept of micro-drenching has also been utilized in other ways for spring crops. A single well-timed micro-drench can be beneficial for some sensitive crops, rather than a series of applications. For example, Syngenta Flowers recommends a single drench of its vigorous TopHat™ begonia, after root establishment, for production in 306 packs to keep them tidy (Figure 2). The application is done early to have no effect on flowering after transplant. Geraniums are another crop that is very sensitive to pacbutrazol and other PGRs. Zonal and Calliope® Geraniums, which can be vigorous growers in late spring, benefit from a single Paclobutrazol drench at a fraction of a part per million (ppm), applied only as the plant is nearly finished or finished. The single application will prevent unruly overgrowth through the sales season.
Figure 2: TopHat™ Pink Begonia. No PGRs (left) vs. 0.25 ppm Bonzi® drench (right)
The single micro-drench concept also expands utility to spring combinations, as brought forth by Drs. Jamie Gibson and Alicain Carlson of Syngenta Flowers last year in an article titled ‘Fillers for Premium Combos’ (GrowerTalks, March 2023, pg. 52-54). The authors tested a single micro-drench on the liners of aggressive filler plants commonly used in container combinations. The drench application produced more controlled growth of the fillers for a neater appearance with less labor. The authors note that treated filler liners can expose sensitive plants in combinations to the PGR and care should be taken when integrating this strategy. Their findings and suggestions for common fillers are outlined in Table 2.
Table 2: Recommended Bonzi® Drench Concentration for Accent Plants2
2Jamie Gibson, Alicain Carlson ‘Fillers for Premium Combos’ GrowerTalks, March 2023, pg. 52-54
Please contact GGSPro for additional information as you consider how micro-drenches may be useful in your operation.
Table 3: Plant Growth Regulators for Height Reduction
* Other sizes available
Note, not all products are registered in all states. Some pesticides are restricted use in some states or regions and not others. It is the responsibility of the applicator to read and follow all label directions, remembering that labels may change. Other products may be safe and effective. Rates, application methods, and edible status are detailed in our GGSPro Insecticide & Fungicide Guides. Griffin also offers the 5th Edition GGSPro Technical Reference Guide in both English and now Spanish versions. This valuable resource outlines a wide range of pest control options and information on pollinator safety, BCA’s, scouting, weed management, plant lighting, nutrition, water quality and more!
Plant growth regulators (PGRs) that can be drenched to control height include Uniconazole, the active ingredient in Sumagic and Concise, Flurprimidol in Topflor, and Paclobutrazol found in Bonzi, Piccolo, Pac O, and Paclo Pro. Of these three active ingredients, Paclobutrazol is inexpensive, less subject to overdosing and stunting, and is the most researched PGR for micro-drench applications (Figure 1).
Figure 1: Lopez, Roberto “What’s All the Hype on Poinsettia Micro-drenches?” GrowerTalks, May 2021, pg. 52-54.
A wide variety of crops are traditionally treated with drenches of Paclobutrazol once or twice near the crop finish date to slow or stop growth for a time. This is a common ‘holding strategy’. This application can put a hard stop on plant growth which may take some time to wear off after the plant is purchased by the consumer. Micro-drenches are done earlier and more often, even weekly, at lower concentrations. The micro-drench method is a soft touch on the brake and not a full stop. Micro-drenches allow flexible control of height for the grower, while still assuring a plant’s ability to grow out for the end consumer. Typical rates used are from 0.10 ppm up to 1.0 ppm for common crops.
For Poinsettias, the considerations are somewhat different as continued growth on the consumer end is not a factor. However, final flower or bract size is a priority along with final height. Bract size of poinsettia can be negatively impacted by any growth retardants applied during the initiation and bract development periods. Therefore, the effect on bracts is a major consideration when choosing a method of height control. The Paclobutrazol micro-drench method has the least influence on bract size when compared to other PGR application options.
Applications to poinsettia can begin once new shoots have elongated after the pinch, generally from late September to early October, and can continue until finish. Graphical tracking of poinsettia height is used to make weekly decisions to apply a micro-drench or not. For vigorous and moderately vigorous varieties, GGSPro recommends rates from 0.10 to 0.125 ppm for growers in the Northern US, and 0.10 to 0.20 ppm for Southern growers. Note, some genetics are compact and naturally low vigorous depending on your location and may not require PGR applications. The reduced PGR dose and optional weekly application frequency of micro-drenching provides the most flexible height control technique. A minimum amount of Paclobutrazol is used and minimal reduction on poinsettia bracts is attained compared to a full drench of 0.5 to 1.0 ppm after October 25th, which can cause a 10-15% reduction in bract size.
For Spring Crops, micro-drenches can begin as soon as the transplant has roots to the edge of the pot and can be carried out throughout the production period, as needed for amenable crops. The goal for these crops is to prevent the need for a full drench late in production, avoiding any negative effect on customer satisfaction.
Table 1 lists guidelines from trials carried out by Dr. Roberto Lopez’s lab at Michigan State University on some common crops. GGSPro recommends starting at the low end of the range when trialing PGRs and designating an un-treated control plant or pack for comparison.
| Crop | PPM Paclobutrazol | Number of Applications | Flower Delay |
|---|---|---|---|
| Angelonia | 0.5 – 1.0 | 3-4 | 5 – 8 days |
| Dianthus | 0.5 – 2.0 | 3 | 1 – 6 days |
| Hibiscus | 0.5 – 1.0 | 1-2 | 3 – 5 days |
| Petunia, Wave | 1.0 – 2.0 | 6 | 4 – 7 days |
| Lantana | 0.25 – 1.0 | 3 | No delay |
| Snapdragon | 0.25 – 0.5 | 4 | 0 – 2 days |
| Sweet Potato Vine | 0.25 – 2.0 | 3-4 | N/A |
| Verbena | 1.0 | 3 | No delay |
The concept of micro-drenching has also been utilized in other ways for spring crops. A single well-timed micro-drench can be beneficial for some sensitive crops, rather than a series of applications. For example, Syngenta Flowers recommends a single drench of its vigorous TopHat™ begonia, after root establishment, for production in 306 packs to keep them tidy (Figure 2). The application is done early to have no effect on flowering after transplant. Geraniums are another crop that is very sensitive to pacbutrazol and other PGRs. Zonal and Calliope® Geraniums, which can be vigorous growers in late spring, benefit from a single Paclobutrazol drench at a fraction of a part per million (ppm), applied only as the plant is nearly finished or finished. The single application will prevent unruly overgrowth through the sales season.
Figure 2: TopHat™ Pink Begonia. No PGRs (left) vs. 0.25 ppm Bonzi® drench (right)
The single micro-drench concept also expands utility to spring combinations, as brought forth by Drs. Jamie Gibson and Alicain Carlson of Syngenta Flowers last year in an article titled ‘Fillers for Premium Combos’ (GrowerTalks, March 2023, pg. 52-54). The authors tested a single micro-drench on the liners of aggressive filler plants commonly used in container combinations. The drench application produced more controlled growth of the fillers for a neater appearance with less labor. The authors note that treated filler liners can expose sensitive plants in combinations to the PGR and care should be taken when integrating this strategy. Their findings and suggestions for common fillers are outlined in Table 2.
| Species | Pinch | Bonzi® Drench Concentration | Comments |
|---|---|---|---|
| Bacopa | Yes | 0.10 – 0.25 ppm | Optional B-Nine at 1250 to 2500 ppm pre-pinch |
| Bidens | Yes | 0.25 – 0.5 ppm | Apply only to vigorous trailing types |
| Euphorbia | Yes | 0.25 – 0.5 ppm | Vigor dependent, acknowledge the vigor of the euphorbia cultivar before application |
| Helichrysum | Yes | 0.10 – 0.25 ppm | Species dependent, lighter concentrations on smaller leaved cultivars |
| Ipomoea | Yes | 0.5 – 1.0 ppm | Liner dip/soak candidate |
| Lobelia | Yes | 0.10 – 0.25 ppm | Optional B-Nine at 1250 to 2500 ppm pre-pinch |
| Lysimachia | Yes | 0.25 – 0.5 ppm | Vigor dependent, concentrations up to 1.0 ppm could be used |
| Swedish Ivy (Plectranthus coleoides) | Yes | 0.25 – 1.0 ppm | Liner dip/soak candidate, also applicable for “ducksfoot” type trailing coleus |
Please contact GGSPro for additional information as you consider how micro-drenches may be useful in your operation.
| Brand | Active Ingredient | Manufacturer | Size | Item Number |
|---|---|---|---|---|
| Bonzi | Paclobutrazol | Syngenta | 1 quart | 70-1260 |
| Bonzi | Paclobutrazol | Syngenta | 2.5 gal | 70-1270 |
| Paclo Pro | Paclobutrazol | Syngenta | 1 gal | 73-1830 |
| Pac O | Paclobutrazol | OHP | 1 gal | 73-1845 |
| Piccolo | Paclobutrazol | Fine | 1 gal | 73-1915 |
| Concise | Uniconazole | Fine | 1 gal | 73-1300 |
| Sumagic | Uniconazole | Nufarm | 1 gal | 73-1951 |
| Topflor | Flurprimidol | SePRO | 2 liter | 73-2005 |
* Other sizes available
Note, not all products are registered in all states. Some pesticides are restricted use in some states or regions and not others. It is the responsibility of the applicator to read and follow all label directions, remembering that labels may change. Other products may be safe and effective. Rates, application methods, and edible status are detailed in our GGSPro Insecticide & Fungicide Guides. Griffin also offers the 5th Edition GGSPro Technical Reference Guide in both English and now Spanish versions. This valuable resource outlines a wide range of pest control options and information on pollinator safety, BCA’s, scouting, weed management, plant lighting, nutrition, water quality and more!