CACTUS

Cactus costs more per unit than most of what the trader carries, 3 emeralds each, and the price makes sense once you notice what it is not: not food, not a seed, not something a crafting table can produce from anything else. It only grows naturally in desert and badlands terrain, so the trade is really selling a shortcut past a trip to that biome.

What people actually want it for has nothing to do with farming. A ring of cactus around a base damages anything that walks into it without a player lifting a sword, which is the usual reason a stack shows up on a shopping list, alongside the odd use as a green dye source or a fast way to pop item frames and boats left sitting nearby.

Placing it is unforgiving in a way seeds and crops are not: it only stands on sand or red sand, and touching anything on any side, block or mob or another cactus, breaks it immediately. That is worth knowing before hauling a stack home expecting it to behave like ordinary building material.

The Wandering Trader sells Cactus for 3 emeralds each, and he does not buy it back once you have it. The offer holds only for a set number of trades before it locks for that visit and never reopens.

No working villager profession touches cactus, buying or selling, at any tier. The trader is the only stall for it, which is unusual for a plain landscape block that a shovel and a walk could get you for free.

He asks 3 emeralds each, and 54 of the other 75 come cheaper. Price is the easy part: he draws his stock from a shared pool, so catching one that happens to be carrying cactus is the real constraint.

The Wandering Trader asks 3 emeralds for a cactus. 8 of the 72 villagers that pay emeralds, emptied out:

3 diamonds against 72 flint for the same 3 emeralds, 24 times the carrying, and the shortest wait is the Fisherman at 1.9 real minutes of shelf, gathering not counted.

The Wandering Trader belongs to no village and works no job block. He turns up wherever you happen to be, two leashed llamas trailing behind, lingers for a while, and eventually leaves whether a trade happened or not. Nothing can be placed or broken near him to change what he is carrying.

He never buys cactus off a player; only six specific goods go into his own pockets and this is not one of them, so it only ever leaves his stock, never enters it. The offer runs until 8 trades have gone through, then locks for the rest of his visit.

What he is carrying today was rolled the moment he spawned, from a list far longer than what fits on one cart, so this particular trader may simply not have cactus. A name tag settles the timing for later: a named mob does not despawn, turning a lucky encounter into a merchant you can return to on purpose instead of by chance.

Weigh the trip before the trade. A stack of 64 runs about 192 emeralds at 3 emeralds each, which usually costs more than the walk to the nearest desert, so this offer is worth taking mainly when you are already stocked up on emeralds and nowhere near sand.

Remember the limit locks for good once all 8 trades on that visit run out, so a big anti-mob fence or golem farm border usually means finding more than one trader over time rather than emptying one cart in a single stop.

Also on the wandering trader's list: acacia sapling, oak sapling, birch sapling, spruce sapling, dark oak sapling and jungle sapling.

Cactus grows on sand without water, and it breaks when it touches a solid block beside it, which is why the classic farm is a column of cactus with a hopper underneath and a block placed at the right height. No redstone and no player attention are needed.

Smelted it becomes green dye, which is the only source of that colour, so a cactus farm quietly feeds a Shepherd's coloured wool trades. It also damages anything that touches it, which makes a border of it a fence that hurts.

A cactus smelted in a furnace gives green dye, and that is the only source of green in the game. No flower gives it, which makes a desert the one biome that has a colour to itself.

Anything that touches a cactus takes damage, items included: a dropped item landing on one is destroyed. That is used deliberately in farms to delete the parts of a drop you do not want.

Cactus grows without water and without light, so a farm can be built underground on sand, which no other plant in the game allows.

At 3 emeralds a block, the wandering trader's Cactus is worth buying exactly once, to plant. How to Build an Automatic Cactus Farm takes it from there.