Welcome to hydroponics, specifically water culture growing! It’s quite complicated, a whole science itself perhaps, but the idea is simple: grow a plant/plants in a soilless or liquid medium. It’s complicated because plants require certain nutrients in various quantities to be available at their roots to survive, their root system also requires a certain amount of oxygen to be available, and furthermore the whole root environment needs to be within a certain pH range for nutrient uptake to take place. All of this applies no matter the medium one grows plants in, but it’s because of all this that hydroponics is complicated, particularly on a micro scale with a single plant in a cup, where there is little buffering to allow for errors - unlike a medium like soil. But it was experiments like yours that lead to the field of both hydroponics, water culture growing, and aquaponics, and a greater understanding of plant functioning and plant nutrient requirements.
Furthermore, you might find the following four part article to be of interest - there’s plenty of other info easily googled, whether on the background history, or the specifics.
Thanks! I've found other sites for folks doing aqua-bonsai... I'm not taking it too seriously, at this point. It's easier for me than dirt, because I can tell at a glance if my poor plant needs water... oh dear, it does... but the fine roots didn't dry out thanks to capillary force.
Weird thing about bonsai, the goal isn't to maximize... more like, I wanna just fail at killing the thing.
