Media surfactant effects on post-production
Growers have little or no control over the conditions theirproducts are exposed to once they leave the production facility. Environmentalconditions likely to affect the performance of greenhouse crops duringpostproduction handling and sales include uneven or infrequent watering, highlight levels, wind and extremes in temperature. Also, high levels of fertilizersalts in pots can exacerbate water stress problems when moisture levels inpostproduction are less than those maintained in the greenhouse. Poor waterrelations in postproduction can lead to premature wilting which may result inpoor plant quality and reduced sales.
Media surfactants (wetting agents, penetrants, wetters)describe a group of products that aids in the wetting and movement of water ingrowing media. Media surfactants act by reducing the surface tension of organiccomponents such as sphagnum peat moss and pine bark, which often develophydrophobic (“water-hating”) properties, particularly underlow-moisture conditions. While the benefits of media surfactants in wettingmedia at planting are well established, there is little information on theirresidual effectiveness after crops leave the greenhouse.
Research conducted at the University of Florida indicates that applications of media surfactant made during production can help alleviate potential wetting problems that arise during postproduction handling and sales, raising the probability of a longer shelf life and greater sell-through. Our experiments indicate that a media surfactant drench prior to shipping can help reduce the stress plants are exposed to in retail display, as well as when consumers do not water adequately.
Applying a Late Drench
We grew out a crop of 4-inch ‘Super ElfinLipstick’ impatiens in a peat-based media that had either been pretreatedwith AquaGro-L (Scotts Co., Marysville, Ohio) at a rate of 3 oz. per cubic yardor left untreated. The crop was hand-watered with a constant feed of 150 ppmnitrogen fertilizer (20-10-20) solution. At the end of production, plants weredrenched with 0 or 600 ppm AquaGroL one day prior to finish. The drench (3 fl.oz. per pot) was applied in the afternoon following a normal morning irrigation.Plants were irrigated again the following morning and placed in a simulatedretail sales Á
setting (outside under clear, plastic cover). Watering waswithheld, and plants were allowed to wilt. When a plant wilted, 200 ml of waterwas applied, and the plant was allowed to wilt again.
The media surfactant drench increased the percentage ofwater retained by pots of wilted impatiens from approximately 50 percent togreater than 80 percent (See Figure 1, page 38). The improvement in mediarewetting was observed whether or not the media had been pretreated. Theimprovement in rewetting after the first wilt had a direct effect on the timeplants took to wilt a second time. As shown in Figure 2, page 41, the drenchhad little or no effect on the time plants took to wilt when first placed inthe simulated retail sales setting. However, because the drench helped toovercome the dry media conditions imposed by the first wilt, the drenchtreatment delayed the second wilt about one day. We have found that mediarewetting and plant wilting will become an even greater problem with eachadditional wilt. The drench helps to break this “vicious cycle” byimproving media rewetting in between successive wilts.
Timing Affects Results
Chrysanthemum ‘Tara’ in 5-inch pots with pretreatedor peat-based media were drenched one week or one day prior to finish with 600ppm AquaGroL at 4 fl. oz. per pot. Plants were allowed to wilt and then 450 mlof water was applied.
The media surfactant drench had a greater effect on mediarewettting when it was applied one day before finish rather than when appliedone week before finish (See Figure 3, page 41). The response was the samewhether or not the media had been pretreated.
A similar experiment with 4-inch Super Elfin Lipstickimpatiens was conducted to see if a higher concentration of media surfactantcould make up for the reduced effectiveness of the drench applied one weekbefore finish. Increasing the media surfactant concentration from 600 to 1,200ppm improved the effectiveness of the earlier application (See Figure 4, page42), but the results were still not as good as when the drench was applied theday before finish.
A follow-up trial with 4-inch ‘Madness Midnight’petunias was conducted to see if media surfactant applied daily in irrigationwater during the last week of production would give similar results as aone-time drench. As with the other trials, media rewetting was measured afterfinished plants were allowed to wilt in a postproduction environment. A dailyapplication of 150 ppm of AquaGroL during the last week of production gavesimilar improvements in media rewetting as a one-time drench application of 600ppm of AquaGroL (See Figure 5, page 42). Lower concentrations applied dailygave improvements over the untreated control but were noticeably less effectivethan 150 ppm.
Application With Subirrigation
Trials were conducted to see if media surfactant could beeffectively applied via subirrigation and if pot size might be an importantfactor. ‘Super Elfin Coral’ impatiens were produced in either4-inch or 6-inch pots using ebb-and-flow subirrigation. At the end ofproduction, one group of pots was allowed to “soak up” 600 ppmAquaGroL by subirrigation. A second group of pots received a 600 ppm AquaGroLdrench. A third group served as an untreated control. Rewetting (200 ml for4-inch pots and 600 ml for 6-inch pots) was evaluated after plants wilted in asimulated retail environment.
Both the drench and subirrigation applications increasedmedia rewetting after wilt (See Figure 6, page 42). The response was similar inboth the 4-inch and 6-inch pots. Although the subirrigation soak was slightlyless effective than the drench, both methods resulted in greatly improvedrewetting.
Drench vs. Maintenance
We grew hibiscus ‘Brilliant Red’ in 1-gallonpots containing a peat-based media for three months. One group of pots receiveda pre-plant drench of 600 ppm AquaGroL Á
(13 fl oz. per pot), a second group received maintenanceapplications (10 ppm AquaGroL at every irrigation), a third group received bothpre-plant and maintenance applications, and a fourth group served as anuntreated control. One day before finish, each of these treatment groupsreceived a late drench treatment of 0 or 600 ppm PsiMatric. In postproduction,plants were allowed to wilt, 1,200 ml of water was applied, and the percentretention determined.
Percent retention of the water applied after wilt wasincreased by the late drench except when both pre-plant and maintenanceapplications were made (See Figure 7, page 44). The late media surfactantdrench had the greatest effect of the late drench when no media surfactant hadbeen applied during production. When either the pre-plant or the maintenanceprogram was followed, the impact of the late drench was reduced. The sameexperiment was conducted in a bark-based media with similar results, exceptthat media rewetting, in general, was less of a problem in the bark mix.
Benefits of a Late Drench
Our experience has been that the drier soilless mediabecomes, the greater the benefit of using media surfactant. In theseexperiments, we evaluated media rewetting at specific plant wilt stages, whichallowed us to measure rewetting at uniformly low media moisture levels. This isbecause plants will generally draw down media moisture to a given level beforewilting. Practically, plant wilt is also the stage at which many consumers orretailers realize that their plants need watering.
Our experiments indicate that media rewetting can beimproved with applications of media surfactant made at the end of production.Most media can be rewetted if enough water is applied, but will enough beapplied? Too often, irrigation practices in retail or by consumers areinadequate to maintain plants in the best condition. A delay in wilting affordedby the late drench may allow several hours or more of better appearance, but isthat enough to make a difference in sales or to maintain them better until thenext watering? Media surfactants are not expensive and can be applied at theend of production via irrigation. Our findings suggest that a late mediasurfactant application may provide some degree of insurance against potentialproblems caused by poor watering practices in postproduction.
We used only one product in our research, but we expect thatother products would also work. AquaGroL was designed for application inirrigation solutions. The performance of other products will depend upon howthe products were developed. For example, there are granular products designedto be incorporated or top-dressed, which may have “slow-release”properties. Strategies for use of granular products will be different thanliquid products.
In conclusion, we found that a pre-ship drench of 600 ppmAquaGroL can improve rewetting of soilless media in postproduction. The preshipdrench was more effective when applied one day prior to Á finish thanone week earlier. Media surfactant can be effectively applied via surface orsubirrigation. If a maintenance program of media surfactant applications isfollowed during production, a late drench may not be warranted. We hope thisinformation will aid growers and water managers in their continued effort tomaximize water-use efficiency and to improve production.