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In 2019–2020, trials were carried out in both intensive (cultivar Moraiolo) and super-high-density (cultivar Sikitita) young olive orchards to drastically reduce early production and, consequently, accelerate tree growth. Different concentrations of naphthaleneacetic acid (NAA) (0 ppm–control, 20 ppm, 40 ppm, 80 ppm, 160 ppm and 250 ppm) were applied at full bloom (open flowers > 80%), using a shoulder sprayer, and their effects on vegetative growth and reproductive behavior were evaluated, also compared to manually deflowered trees. The treatments with NAA reduced fruit set (down to values close to zero) compared to the control, and the reduction was correlated with the NAA concentration. In particular, 160 ppm virtually eliminated fruit set and thus production in both Moraiolo and Sikitita cultivars. In Moraiolo, 160 ppm NAA and manual deflowering determined similar shoot and trunk growths, which were greater than in control trees. Application of 160 ppm NAA for two consecutive years gave a progressively higher increase in trunk growth compared to the control. In conclusion, in young olive trees, the treatment with 160 ppm NAA at full bloom practically eliminated fruit set and production, with a parallel great increase in vegetative growth. This can be exploited as a powerful technique to accelerate the growth of young olive trees in both intensive and super-high-density orchards, as well as in nurseries. A more rapid transition to the adult stage/size of the trees and to full production of the orchard allows us to anticipate the use of mechanical harvesting and the recovery of the planting investment.

Experiments were carried out in 2018 and 2019 to evaluate the effects of a biostimulant of animal origin, with a hormone-like action, on the growth and physiology of young olive trees. The biostimulant, consisting of a complex of natural amino acids (glycine, proline, and hydroxyproline, etc.), was applied by fertigation to both potted (one-year-old) and field-grown (2 years after transplanting) young olive trees. The control consisted of trees treated with an amount of urea nitrogen equal to the total nitrogen supplied with the biostimulant. Potted trees treated with the biostimulant showed greater growth than the control soon after treatment and up to the end of the vegetative season. Generally, this was associated with higher leaf photosynthetic rates and stomatal conductance. At the end of the experiment, all tree parts (roots, stem, shoots, and leaves) of the treated trees had greater biomass than the control. The trunks of field-grown trees treated with the biostimulant had greater growth with respect to the control. Overall, the results indicate the possibility of using the biostimulant based on complexes of natural amino acids to promote the growth of young olive trees.