Layered cactus farm

A layered cactus farm by Triloms, designed by iMineCrazy. Cacti sit on sand in a glass box with fence posts beside them, so the moment a cactus grows into the fence it breaks off, falls down a gap and lands on a hopper into a chest. The whole thing stacks upward, each layer identical, and the layer count is the only thing that sets the rate. It is the cheapest possible design and it has one real weakness, which is that cacti destroy any dropped item that touches them, so a fair share of the harvest never reaches the chest.

Cacti delete any dropped block that touches them. indy-dog2 says place the fences before the cacti, or bring spares, having learned it the hard way.
The same mechanic eats the harvest. studionakamura describes the chain: the cactus pops off, hits the cactus growing beside it and vanishes, then hits more on the way down. smoothierip5693's fix is to swap the fence posts for glass blocks.
The middle row of fences does nothing. bulletmaster and re4lity176 both drop it and the two side rows still reach every cactus.
Put the hopper one block below the bottom floor. denisvarga2794 found that level with the floor the cactus slides up to the hopper and stops instead of going in.
Going up to the second layer takes four blocks, not three. Ytjokers says the oak fence is in the way otherwise.
The glowstone is doing nothing. leonardomurgia4959 tested it on 1.21.4 and cacti grow at exactly the same rate in complete darkness.