8/9/2019 Hydrangea Grouth Regulators

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ontrolling Height of Hydrangeas WithGrowth Retardants

H. C . K O H L J R . R L N E L S O N

Treatment of hydrangea plants with thegrowth reta.rdant B-Nine i s a promising

method for saving production costs. The

shorter plants do not have to be staked,

and blooms are often more beautifu l than

untreated plants.

wo HYDRANGEA varieties, Straffordnd Rose Supreme, were grown from

Oregon cuttings at the University of Cal-ifornia, Los Angeles, during the summergrowing season of 1953 OP 4ugust 12all plants were hand-pinched to two good

pairs of leaves per stem, af ter which theybroke and grew vigorously. On Septem-ber 16 they were moved out-of-doors, andon October 23 the growth retardan ts Cy-cocel and B-Nine were applied as sprays- e a c h in two concentrations, 2,000 ppmand 4,000 ppm-to six plants in eachtreatment, with six plants of each varietyuntreated for controls.

Cycocel was not effective in decreasingeither the length of the forced stems orthe overall height of the plants. B-Nine,on the other hand, proved effective: theshor ter plants were more handsome spec-

imens than the untreated plants seephotographs) and indicate the possibilityof a considerable saving in productioncosts becaupe they can be marketed with-out staking. Although the number of in-florescences per plant was somewhat re-duced by the higher 4,000 ppm) B-Ninetreatment, the inflorescence weight perplant which should be a fair measure ofshowiness) was not reduced see tab le) .

Commercial growers who may want totry the B-Nine treatment should be awareof the onset of dormancy, since it differsfrom area to area. Timing is a vital part

of the trea tment. The spray must be ap-plied after the current season growth hasfinished and flower bud form ation hasstarted.

Harry C . Kohl Jr. is Professor oLandscape Horticulture and Plant Ph ysi-ologist in the Experiment Station; andRobert L. Nelson s Laboratory Techni-cian in the Departme nt of L andscapeHorticulture Uni versity of Californ iaDavis.

GROWTH A ND FLOWERING DATA (AVERAGES) FOR HYDRANGEAS TREATED WITH AN D WITHOUTGROWTH RETARDANT SPRAYS

Fresh weight Weight ofVariety Retardant Concentration* Length Of per inflorescences

new s o o t s per plant inflorescence per plant

oom cm number am om~

Strafford None 41.4 6.5 23.8 155Cycocel 2000 40.9 5.7 33.7 192Cycocel 4000 38.5 5.9 29.6 1758-N ne 2000 28.0 5.7 26.7 1538-Nine 4000 15.5 5.3 30.7 163

Rose Supreme Non e 40.0 5.1 33.9 173Cycocel 2000 38.2 6.1 24.8 151Cycocel 4000 40 3 5.8 31.0 1758-Nine 2000 30.8 5.8 30.0 1748-Nine 4000 20.1 4.6 40.5 186

~

*Concentration refers to active ingredient in the sproy solution.

Effects of B -Nine grow th ret ardan t in shortening hyd rang ea plants are shown in photos o Rose

Supreme, above, and Straff ord vari ety, belo w. Plants to lef t had been treated with B-Nine at aconcentration of 4 000 ppm; and center plants at 2,000 p p m -a s compared with untreated checkplants to right.

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