Hey guys! Psionic_Nova here with a small project I decided to share. This is the cactus farm I personally use in my Survival world, I have modified it and tweaked it, and finally have an end product. The farm uses minimal resources, including no need for Slime Balls, which can be hard to get if you don't live by a swamp.

Farm Specifications:

Yield of 40 Cacti per harvest( Taking into account replanted Cacti)
Consistent Drop Rate of 100% (No Cacti Lost)
Uses 11 Redstone, 6 Repeaters, 7 Redstone Torches, 20 Cacti, 5 Pistons( Non-Sticky), 5 Red Sand, 20 Sand, 1 Button, and Building Blocks of your choice.

If you have the resources, you can place many side-by-side to create a larger farm.

I hope you found this helpful! You can use this in your SSP world or on a Server.!

Additional Notes

How it Works:

Under each block of red sand there is one piston, aiming upwards.
When the button is pressed, each block of red sand is pushed upward, causing the cacti around it to break, as cacti cannot have a block directly beside it.
After the pistons retract, the red sand falls into its original position.
If all cacti are at full height, 60 cacti are dropped, 20 to replant, and 40 to do what you wish with.
Once the cacti are replanted around the red sand the farm is fully reset.