Global climatic changes limited the fresh water supply, which led to increasing the need for irrigation water. For this reason, the main objective of this study was to investigate the role of humic acid (HA), salicylic acid (SA) and thiamin (Vitamin B1) in increasing the Duranta plumeri resistance to irrigate with diluted seawater. The experiment was conducted on Duranta plumieri, (synonym to Duranta erecta L.) during the two successive seasons of 2014 and 2015 to estimate the effects of soil application with humic acid at 1000 and 2000ppm concentrations and foliar spraying plants with salicylic acid  or thiamin at 250 and 500ppm combined with irrigation with diluted seawater at three concentrations: 2000, 4000 and 6000ppm on vegetative growth and associated with physiological parameters. The results revealed that the plant vegetative growth parameters were considerably affected by salinity stress. Plant height, the number of branches/plant and shoot fresh and dry weight were linearly decreased with the increasing in saline water concentration. Also, salt stress was negatively affected the total carbohydrate contents, photosynthetic pigments, reducing and non-reducing sugars and mineral uptake ( N,P,K and  Mg) as well as higher contents of Na⁺ and Cl^- elements. In contrast to this, SA, B1 or humic acid were induced a stimulatory effect on the all vegetative growth parameters in plants which irrigated with all diluted seawater concentrations. The highest values of vegetative parameters and total chlorophylls were obtained with humic acid at 1000 and 2000ppm concentrations under all salinity concentrations. SA enhanced the physiological processes in Duranta plants under saline conditions through increasing significantly the total carbohydrate and carotenoids contents, and reducing and non-reducing sugars. The exogenous application of thiamin significantly increased proline content in salinity stressed plants. The greatest contents of N,P,K and Mg in plants under salinity stress were obtained with soil application of humic acid followed them with the treatment of spraying with SA and B1. Also, these treatments led to decrease the contents of Na⁺ and Cl^-. It could be recommended that soil application with humic acid at 2000ppm can ameliorate the negative effects of irrigation with diluted seawater up to 6000ppm salinity concentration and spraying Duranta plants with SA or B1 at 500ppm increased the growth and physiological processes under 4000ppm salinity.