SUMMARYPotted Osteospermum hybrida plants grown in a greenhouse during the Winter were irrigated with water having electrical conductivities (EC) of 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 or 5.0 dS m−1. The following relationships were studied in order to improve the management of saline irrigation systems using soil moisture and EC sensors: pore water EC (ECPW) using the pour-through method (ECPWPT) vs. ECPW estimated using a GS3 sensor (ECPWGS3); ECPWPT vs. bulk EC (ECB); ECPWPT vs. leachate EC (ECL); and ECPWGS3 vs. ECB. The tolerance of Osteospermum plants to salinity was also determined. Bulk EC, ECPWGS3, and ECL values were closely and positively correlated with ECPWPT. ECL over-estimated ECPWPT, while ECPWGS3 underestimated ECPWPT. Estimation of ECPWGS3 (by the Hilhorst Model) was not accurate due to the influences of humidity, salinity, and temperature. The higher the irrigation water EC (ECIW), the greater the variability in all measurements made of EC. Increases in ECIW reduced plant height, diminish...