Left-side water radical, the three-drop form of 水. Carries the meaning: 滋 is water nourishing growth - to moisten, to feed, to make flourish, as in 滋润 to refresh and 滋养 to nurture. Same indexing radical as 润 to moisten, 浇 to water, 溉 to irrigate.
Right side 兹 supplies the sound - zī stays zī with no shift. The 'this, now' demonstrative meaning is not active; 兹 is a sound tag. 兹 itself depicted two thread bundles growing thick, which faintly echoes the flourishing-growth core of 滋.
