S)3Water Use and Growth of Eil
Central Florida Re
Growth retardants are being us,
from holding a finished 3-inch pot cro
an interior environment. Slowing plar
treatment but other effects could also I
Many researchers have reported
resistance to drought stress as an effect
research, poinsettias and beans treated
transpiration than untreated plants, yet
altered (1). Paclobutrazol treated chr)
stomatal apertures and thicker cuticle,
containerized plant was designated as an experimental unit. Six replications per species were
made for each of the 5 rates of growth regulator tested.
Plants were placed in greenhouses where maximum light intensity at bench level was
1000 ft-c and air temperatures ranged from 70 to 90"F. On 10 March 1992, a 100 ml
BonziTM (ICI Americas, Inc., Goldsboro, NC) (containing 0.4% active ingredient
paclobutrazol) solution at 0.25, 0.50, 0.75 or 1.0 ml/liter, or 100 ml of tap water was
poured onto the surface of each pot. Containers were top-dressed on 13 March 1992 with
19-6-12 Osmocote 3-month fertilizer at 5 g/6-inch pot.
Throughout the course of the experiment, volume of irrigation water supplied to each
plant was closely monitored to determine evapotranspiration for each species. Individual
species were watered by hand 1 to 3 times per week as needed to promote healthy growth.
At each watering, tap water was poured onto growing medium until 30 to 50 ml leachate was
collected in 2000 ml beakers placed underneath pots for that purpose. Total volume of
leachate collected subtracted from total amount of water applied determined total
evapotranspiration rate for each plant.
Leachate electrical conductivity levels and pH were determined for croton, using the
pour-through method, on 3 March and 28 May 1992. Plant height or vine length of all eight
species tested was measured on 29 May 1992.
Results and Conclusion
Growth of all species was affected by drenches containing paclobutrazol (Table 1).
Although effects varied for each species tested and paclobutrazol application rate received,
the biggest difference in plant size for each species was found when height of plants treated
at the lowest rate were compared to height of untreated plants.
Paclobutrazol treated plants had less total evapotranspiration than those receiving only
water drench (Table 2). Paclobutrazol treatments had more effect on evapotranspiration of
species whose growth was most affected by the growth regulator.
Electrical conductivity (imhos/cm) of medium leachate collected from pots of
schefflera on 28 May 1992 was greatest from containers receiving 1.00 ml BonziTM, the
highest rate tested '(Table 3). Leachate pH decreased for all 5 drench formulations over
time. Drop in pH over time was generally greater as paclobutrazol concentration in drench
increased. These results could indicate less fertilizer consumption by plants receiving
drenches containing more paclobutrazol.
Data collected in this experiment show water, and possibly, fertilizer needs of plants
treated with paclobutrazol drenches were significantly less than those of untreated plants,
even for species whose growth was least affected by paclobutrazol. Paclubutrazol used to
reduce foliage plant water use may be feasible if costs of treatment are less than savings
realized from reduced labor, fertilizer and equipment use.
1. Barrett, J.E. and T.A. Nell. 1979. Effects of growth retardants on plant water use.
Proc. Plant Growth Regulator Working Group 6:69-74.
2. Biernbaum, J., W. Carlson and R. Heins. 1989. Limit runoff with slow release
fertilizers, quality media, wetting agents and absorbent gels. Grower Talks 53(5):48,
3. Elliott, G. 1990. Reduce water and fertilizer with ebb and flow. Greenhouse
Grower 8(6):70-72, 74-75.
4. Halevy, A.H. and B. Kessler. 1963. Increased tolerance of bean plants to soil
drought by means of growth-retarding substances. Nature 197:310-311.
5. Latimer, J.G. 1992. Drought, paclobutrazol, abscisic acid and gibberellic acid as
alternatives to daminozide in tomato transplant production. J. Amer. Soc. Hort. Sci.
6. Martens, J.A. 1991. Growing in the year 2000: making zero runoff a reality.
Grower Talks 54(9):21-22, 24, 26, 28.
7. Smith, E.F., A.V. Roberts and J. Mottley. 1990. The preparation in vitro of
chrysanthemum for transplantation to soil. 2. Improved resistance to desiccation
conferred by paclobutrazol. Plant Cell Tissue Organ Cult. 21:133-140.
8. Swietik, D. and S.S. Miller. 1983. The effect of paclobutrazol on growth response
to water stress of apple seedlings. J. Amer. Soc. Hort. Sci. 108:1076-1080.
9. Wilkerson, D.C. 1990. Irrigation management and our natural resources. Florida
10. Zimmer, B. 1990. New look at irrigation. Greenhouse Manager 9(5):110-112, 114,
Table 1. Height or vine length a
paclobutrazol. Plants I
BonziTM, ml/6- Begonia coccinea
inch potz 'Pink'
Table 2. Evapotranspiration fi
rates of paclobutrazc
BonziT, ml/6- Begonia
inch potz coccinea
rable-. Electrical conductivity
variegatum 'Petra' drer
from 3 March until 29
BonziTM, ml/6-inch potz
Containers were drenched with a 100