Media surfactant effects on post-production

April 2, 2002 - 13:54

Research at the University of Florida has shown that media surfactants help alleviate the effects of inadequate watering during post-production handling and sales.

Growers have little or no control over the conditions their
products are exposed to once they leave the production facility. Environmental
conditions likely to affect the performance of greenhouse crops during
postproduction handling and sales include uneven or infrequent watering, high
light levels, wind and extremes in temperature. Also, high levels of fertilizer
salts in pots can exacerbate water stress problems when moisture levels in
postproduction are less than those maintained in the greenhouse. Poor water
relations in postproduction can lead to premature wilting which may result in
poor 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 in
growing media. Media surfactants act by reducing the surface tension of organic
components such as sphagnum peat moss and pine bark, which often develop
hydrophobic (“water-hating”) properties, particularly under
low-moisture conditions. While the benefits of media surfactants in wetting
media at planting are well established, there is little information on their
residual 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 Elfin
Lipstick’ impatiens in a peat-based media that had either been pretreated
with AquaGro-L (Scotts Co., Marysville, Ohio) at a rate of 3 oz. per cubic yard
or left untreated. The crop was hand-watered with a constant feed of 150 ppm
nitrogen fertilizer (20-10-20) solution. At the end of production, plants were
drenched 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 simulated
retail sales Á

setting (outside under clear, plastic cover). Watering was
withheld, and plants were allowed to wilt. When a plant wilted, 200 ml of water
was applied, and the plant was allowed to wilt again.

The media surfactant drench increased the percentage of
water retained by pots of wilted impatiens from approximately 50 percent to
greater than 80 percent (See Figure 1, page 38). The improvement in media
rewetting was observed whether or not the media had been pretreated. The
improvement in rewetting after the first wilt had a direct effect on the time
plants took to wilt a second time. As shown in Figure 2, page 41, the drench
had little or no effect on the time plants took to wilt when first placed in
the simulated retail sales setting. However, because the drench helped to
overcome the dry media conditions imposed by the first wilt, the drench
treatment delayed the second wilt about one day. We have found that media
rewetting and plant wilting will become an even greater problem with each
additional wilt. The drench helps to break this “vicious cycle” by
improving media rewetting in between successive wilts.

Timing Affects Results

Chrysanthemum ‘Tara’ in 5-inch pots with pretreated
or peat-based media were drenched one week or one day prior to finish with 600
ppm AquaGroL at 4 fl. oz. per pot. Plants were allowed to wilt and then 450 ml
of water was applied.

The media surfactant drench had a greater effect on media
rewettting when it was applied one day before finish rather than when applied
one week before finish (See Figure 3, page 41). The response was the same
whether or not the media had been pretreated.

A similar experiment with 4-inch Super Elfin Lipstick
impatiens was conducted to see if a higher concentration of media surfactant
could make up for the reduced effectiveness of the drench applied one week
before finish. Increasing the media surfactant concentration from 600 to 1,200
ppm improved the effectiveness of the earlier application (See Figure 4, page
42), but the results were still not as good as when the drench was applied the
day before finish.

A follow-up trial with 4-inch ‘Madness Midnight’
petunias was conducted to see if media surfactant applied daily in irrigation
water during the last week of production would give similar results as a
one-time drench. As with the other trials, media rewetting was measured after
finished plants were allowed to wilt in a postproduction environment. A daily
application of 150 ppm of AquaGroL during the last week of production gave
similar improvements in media rewetting as a one-time drench application of 600
ppm of AquaGroL (See Figure 5, page 42). Lower concentrations applied daily
gave improvements over the untreated control but were noticeably less effective
than 150 ppm.

Application With Subirrigation

Trials were conducted to see if media surfactant could be
effectively applied via subirrigation and if pot size might be an important
factor. ‘Super Elfin Coral’ impatiens were produced in either
4-inch or 6-inch pots using ebb-and-flow subirrigation. At the end of
production, one group of pots was allowed to “soak up” 600 ppm
AquaGroL by subirrigation. A second group of pots received a 600 ppm AquaGroL
drench. A third group served as an untreated control. Rewetting (200 ml for
4-inch pots and 600 ml for 6-inch pots) was evaluated after plants wilted in a
simulated retail environment.

Both the drench and subirrigation applications increased
media rewetting after wilt (See Figure 6, page 42). The response was similar in
both the 4-inch and 6-inch pots. Although the subirrigation soak was slightly
less effective than the drench, both methods resulted in greatly improved
rewetting.

Drench vs. Maintenance

We grew hibiscus ‘Brilliant Red’ in 1-gallon
pots containing a peat-based media for three months. One group of pots received
a pre-plant drench of 600 ppm AquaGroL Á

(13 fl oz. per pot), a second group received maintenance
applications (10 ppm AquaGroL at every irrigation), a third group received both
pre-plant and maintenance applications, and a fourth group served as an
untreated control. One day before finish, each of these treatment groups
received 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 percent
retention determined.

Percent retention of the water applied after wilt was
increased by the late drench except when both pre-plant and maintenance
applications were made (See Figure 7, page 44). The late media surfactant
drench had the greatest effect of the late drench when no media surfactant had
been applied during production. When either the pre-plant or the maintenance
program was followed, the impact of the late drench was reduced. The same
experiment was conducted in a bark-based media with similar results, except
that 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 media
becomes, the greater the benefit of using media surfactant. In these
experiments, we evaluated media rewetting at specific plant wilt stages, which
allowed us to measure rewetting at uniformly low media moisture levels. This is
because plants will generally draw down media moisture to a given level before
wilting. Practically, plant wilt is also the stage at which many consumers or
retailers realize that their plants need watering.

Our experiments indicate that media rewetting can be
improved with applications of media surfactant made at the end of production.
Most media can be rewetted if enough water is applied, but will enough be
applied? Too often, irrigation practices in retail or by consumers are
inadequate to maintain plants in the best condition. A delay in wilting afforded
by the late drench may allow several hours or more of better appearance, but is
that enough to make a difference in sales or to maintain them better until the
next watering? Media surfactants are not expensive and can be applied at the
end of production via irrigation. Our findings suggest that a late media
surfactant application may provide some degree of insurance against potential
problems caused by poor watering practices in postproduction.

We used only one product in our research, but we expect that
other products would also work. AquaGroL was designed for application in
irrigation solutions. The performance of other products will depend upon how
the products were developed. For example, there are granular products designed
to be incorporated or top-dressed, which may have “slow-release”
properties. Strategies for use of granular products will be different than
liquid products.

In conclusion, we found that a pre-ship drench of 600 ppm
AquaGroL can improve rewetting of soilless media in postproduction. The preship
drench was more effective when applied one day prior to Á finish than
one week earlier. Media surfactant can be effectively applied via surface or
subirrigation. If a maintenance program of media surfactant applications is
followed during production, a late drench may not be warranted. We hope this
information will aid growers and water managers in their continued effort to
maximize water-use efficiency and to improve production.

About The Author

Jeff Million is a research associate and Jim Barrett is a professor in the Department of Environmental Horticulture, University of Florida, Gainsesville, Fla. They may be reached by phone at (352) 392-9806 or E-mail at jmillion@mail.ifas.ufl.edu.

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