Influence of pinching and growth retardant on the growth of lavender

Department of Ornamental Plants and Landscape Architecture

Faculty of Agriculture

University of Zagreb

Svetošimunska 25

10000 Zagreb

The objective of the study was to determine the influence of pinching and/or application of growth retardant on the growth of lavender (Lavandula vera) cv. Lady grown as a pot plant.

Plants were pinched at the beginning of the growing period and/or treated two times with a daminozide-based growth retardant (Alar 85), in 0.1% and 0.2% solutions, at an interval of 15 days. The trial was set up according to the randomized block scheme with five replications.

Plants that were not pinched were taller (27.5%) than pinched and there were no statistically significant differences between them regardless of the daminozide treatment. A difference at 1% level was recorded only between untreated plants and plants treated with a 0.2% daminozide solution. Plants that were not treated with daminozide had the largest number of lateral branches (6.0% more) while plants treated with a daminozide solution of lower concentration had the smallest number of lateral branches (2.2% less). Regardless of the daminozide treatment, pinched plants had a smaller number of lateral branches (2.33% less) compared to plants that were not pinched.

Pinching and growth retardant application influenced the height and the number of lavender lateral branches. The lowest plants were obtained with pinching and application of a daminozide solution of lower concentration. Growth retardant application, however, had an adverse effect on the number of lateral branches.
INTRODUCTION
Lavender (Lavandula vera DC.), semi-shrub originating from the Mediterranean, may reach the height of 30 to 60 cm. It grows in sunny, dry, rocky habitats on limestone (Hansen and Stahl, 1993; Jelitto and Schacht, 1995). The whole plants are characterized by their decorativeness, owing to the evergreen grey-green leaves oppositely distributed along the stem. The flowers appear towards the beginning of summer in terminal flower spikes of white, pink to dark purple colour, depending on the cultivar (Armitage, 1997). Apart from their decorative value, they are well known by their use for the extraction of essential oil applicable in pharmaceutical and cosmetic industries.

For the purpose of expanding the assortment of pot plants of many kinds of perennials, including lavender, growth retardants are used in cultivation in order to reduce vegetative growth, obtain compact plants, and encourage flowering.

Daminozide is one among the growth regulators slowing down the biosynthesis of gibberelins and encouraging flowering (Halevy, 1990). Since it meets the conditions for wide application, it is one of the most frequently used growth retardants in horticulture (Davis and Andersen, 1989).

Lavender plants are fairly compact and shrubby, but the stem of the inflorescence may elongate excessively. In growth regulator trials, conducted by Withman et al., 1996 A-Rest and Sumagic effectively controlled this elongation. Good success was achieved by using one or more applications of Sumagic in solution of 5-10ppm on 'Munstead' lavender.

For the purpose of obtaining low compact plants, pinching is also performed in some kinds of ornamental plants. Removal of the shoot apex by decapitation, or pinching out the growth tip, removes the source of apical dominance and induces out growth of lateral buds.
MATERIAL AND METHODS
The influence of daminozide and/or pinching on the growth of the Lavandula vera DC. cv. Lady, cultivated in greenhouse, was studied in the period from the first application of daminozide, in April, until May, when the pot plants were ready for sale. The seed was sown in multipot plates on 19^th January. In the third decade of February, the plants were transplanted into plastic pots with the volume of 500 ml, into a substrate consisting of TKS 1 and peat. The trial was set up according to the randomized block scheme with five replications with six combinations and ten plants per combination.

The first combination included control plants cultivated without pinching or daminozide application (A0P0). The second combination included pinched plants with daminozide application (A0P1). The third and fourth combination included daminozide application in a 0.1% solution, with the first one not being pinched (A1P0), and the other one being (A1P1). The fifth and sixth combination included daminozide application in a 0.2% solution, also without (A2P0) and with (A2P1) pinching.

The plants were pinched above the fully developed apical leaf on 11^th April, when the first treatment using 0.1 and 0.2% daminozide concentrations was also performed, according to the experimental scheme. The second daminozide treatment followed after two weeks, on 26^th April.

Before the beginning of the sale, on 21^st May, we measured plant height (cm) and the number of lateral branches, in order to establish the influence of daminozide and pinching on the growth of lavender plants.

Plants treated with a 0.2% daminozide solution were the lowest on the average (3.4% lower than the average), while those not treated with daminozide were the highest on the average (4.2% higher than the average).

The highest (8.33cm), as may be seen from Graph 1, were the control plants, which were not pinched or treated with daminozide. In the case of non-pinched plants, the impact of daminozide increased with its concentration. Plants treated with daminozide solution of lower concentration (0.1%) had no statistically significant difference from the control, or from the plants treated by the daminozide solution of higher concentration (0.2%). The difference at the level of 1% was only between the plants from the control group and the non-pinched plants treated by the 0.2% daminozide solution.

Non-pinched plants were higher (27.5%) with regard to those pinched. The lowest on the average (5.42cm) were pinched plants treated with the lower concentration daminozide solution, while the highest on the average (5.89cm) were pinched plants treated by the 0.2% daminozide solution. However, among them there was no significant statistical difference, regardless of the daminozide treatment.

The application of a 0.5% daminozide solution on Aster novi-belgii, in a trial conducted by Whipker et al. in 1995, caused plant height lowering by 29, i.e 24% respectively, depending on the cultivar. A significant lowering of the plant height using daminozide was also recorded by Kheshem et al., in 1988, for tomato, and Whipker et al., in 1994, for ornamental kale.

In an experiment with oleander (Nerium oleander L.) conducted by Bañón et al. in 2000, pinched plants were significantly shorter than non-pinched plants, while CCC was less effective than pinching in reducing growth.

The lowest number (11.29 and 11.51) of lateral branches was recorded with pinched plants treated with daminozide, regardless of concentration.

In a trial conducted by Yoo YongKweon et al. (1999) on Chrysanthemum zawadskii ssp. naktongense, pinching caused a lowered number of shoots per plant.
CONCLUSIONS
Pinching and growth retardant application had a considerable influence on the lowering of plant height. The lowest plants (5.62cm) were obtained with pinching and application of daminozide regardless of the solution concentration. The biggest number of (12.45) lateral branches was found in plants not treated with daminozide regardless of pinching. Pinched plants not treated with daminozide solution (A0P1) were the lowest (5.56cm), with the highest number of lateral branches (12.36).
REFERENCES
Armitage, A. 1997. Herbaceous Perennial Plants. Stipes Publishing, L.L.C., Champaign, Illinois

Bañón, S.; Franco, J.A.; Fernández, J.A.; Ochoa, J.; González-Benavente, A. 2000. Growth development and leaf colour responses of oleander (Nerium oleander L.) to pinching and chlormequat chloride treatment

Davis, T.D.; Andersen, A.S. 1989. Growth retardants as aids in adapting new floricultural crops to pot culture. Acta Horticulturae 252, 77-85

Halevy, A. H., 1990: Recent advances on flowering in horticultural crops. Advances in Horticultural Science, (4)1:39-43.Hansen, R.; Stahl, F. 1993. Perennials and their garden habitats, Cambridge

Jelitto, L., Schacht, W., 1995. Hardy Herbaceous Perennials. Timber Press, Portland, Oregon

Kheshem, S.A.; Kochan, W.J.; Boe, A.A.; Everson, D.O. 1988: Calcium Translocation and Tomato Plant and Fruit Responses to Molybdenum and Daminozide. HortScience 23(3): 582-584

Levy, Miriam 1998. Ball RedBook16^thEdition, Vic Ball, Batavia, Illinois, USA

Yoo YongKweon; Kang SangWook; Kim HyunKyung 1999. Effects of pinching and daminozide treatment on growth and flowering of Chrysanthemum zawadskii ssp. naktongense. Journal of the Korean Society for Horticultural Science 40(5) 598-602

Whipker, B. E., Eddy, R. T., Hammer, A., 1994: Chemical Growth Retardant High Control of Ornamental Kale. HortScience 29(4): 329

Whipker, B. E., Eddy, R. T., Heraux, Farah, Hammer, A., 1995: Chemical Growth Retardants for Height Control of Pot Asters. HortScience 30(6): 1309.

Withman, Catherine; Heins, R.; Cameron, A.; Carlon, W. 1996 Rising up Perennials. Greenhouse Grower. Michigan State University.

Graph 1: Average Plant Height

Graph 2: Average Number of Lateral Branches