I've had this cactus for a few years, and for a while it's had a problem where it grows so tall that it can't stand up. You can see in the photo that I have it tied to some stakes to keep it upright - if not for those it would literally uproot itself in under a day.
Why might this be? I don't know all that much about houseplants. I water this cactus (and my other cactuses, which are not the same species) once every two weeks, about 1 to 1.5 cups of water. I use some cactus fertilizer like twice a year, pretty inconsistently. It lives perpetually indoors with those three light rods visible in the picture as its sole light source (On for 12 hours a day).
Given how little I know about proper plant care, I'm sure none of that is ideal - but is any of it the obvious culprit for why this happens? What should I be doing better?
Thanks for any help.
P.S. Those two nodules just above the lower string are brand new, and it's never branched out like that before - what should I expect them to become? Round bulbs? Branches? Flowers? Nothing at all? The tip top of the cactus being white is also very recent.
I'm by no means an expert on plants, but usually they grow thin and long if they need (more) light. Could you relocate it closer to a window where it gets sun light? And naybe it is confused because the light comes from its sides rather than from the top.
I honestly can't put it near a window - there are only 2, and they both get pretty limited sun from like 6pm to 8pm. I did originally keep it on the back porch (Which I'm not convinced gives more light than the light rods), but I moved it in when it kept getting bugs. I can look into ways to get it more artificial lighting, though.