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farms[difficulty:beginner][version:26.3]

Kelp farm in Minecraft 26.3: automatic kelp for dried kelp blocks, the cheapest fuel in the game

Kelp grows on its own underwater, an observer can see each growth step, and a piston can break it without killing the plant. That makes a fully automatic kelp farm cheap to build. Here is how growth works, the observer-piston module, collection, and why dried kelp blocks are the best renewable fuel.

David Riperson4 min read
A row of kelp plants with observers and pistons in an automatic Minecraft kelp farm

Coal runs out. Kelp does not. A kelp farm turns a few blocks of ocean into an endless supply of dried kelp blocks, and each one smelts 20 items in a furnace, more than a piece of coal. Pair the farm with an automatic smelter and you never think about fuel again.

RateDepends on plant count, roughly one block per plant every 8 minutes
XP levelFrom smelting
Build time20 minutes for a 10-wide farm
DifficultyBeginner

How kelp grows

The design depends on three facts:

  • Kelp grows one block at a time on random ticks. At the default tick speed, each plant grows about once every 8 minutes on average.
  • Kelp has an age. When planted it gets a random age, and each growth step adds one until it stops at the maximum. A tall kelp eventually stops growing on its own.
  • Breaking part of a stalk only removes what is above it. The block below keeps growing, and it gets a fresh random age, so a stalk you keep cutting back never "runs out".

So the trick is: let kelp grow one block above its base, cut it right there, and the base grows again forever.

The observer and piston module

Build one column per plant, then repeat it in a row.

  1. Floor: a row of solid blocks (dirt, sand or stone) on the sea floor or in a glass tank.
  2. Plant kelp on each floor block, fully underwater.
  3. Observer: place an observer one block above the kelp's base block, at the side, with its face looking at that second block. When kelp grows into the second block, the observer fires.
  4. Piston: place a piston next to the second block, facing it, and power it from the observer. When the kelp grows up, the piston extends into that block and breaks the kelp.
  5. Water: keep the whole column of the plant underwater. Kelp needs water source blocks to grow in.

The base block stays, the broken piece pops off as a kelp item, and the plant starts growing again.

Do not cut the base. If the piston breaks the bottom block, the plant is gone. The piston must sit at the second block, never at the first.

Kelp farm parts: kelp, observer, piston, hopper, dried kelp and a dried kelp block that smelts 20 items Image: SyntaxMine, made from Minecraft's own textures.

Collecting the kelp

Broken kelp items float upward in water. Two common ways to catch them:

  • A water stream to hoppers. Put a flowing water channel above the farm that carries floating items to one side, ending over a hopper that feeds a chest.
  • Hopper minecarts. A rail with hopper minecarts above the farm, against the top of the tank, picks items up through blocks or straight from the water.

For a first farm, the water stream is easier to get right.

Turning kelp into fuel

  1. Smelt kelp into dried kelp in a furnace or a smoker (twice as fast, and the smoker is cheap).
  2. Craft 9 dried kelp into a dried kelp block.
  3. Use dried kelp blocks as fuel: each smelts 20 items.

The neat loop: once the farm runs, feed some of the dried kelp blocks back into the smoker that dries the kelp. The farm pays for its own fuel and still produces a surplus.

Fuel Items smelted Renewable
Coal or charcoal 8 Charcoal yes
Dried kelp block 20 Yes
Block of coal 80 Only from coal
Lava bucket 100 Yes, with a lava farm

Making it faster

  • More plants, not taller plants. Output scales with the number of bases. A 20-wide farm makes twice what a 10-wide one does.
  • Two layers. Stack a second row of the module above the first, each with its own floor and water.
  • Keep it loaded. Like every crop farm, kelp only grows in loaded chunks, so build it near where you play.

Frequently asked questions

How does an automatic kelp farm work?

An observer watches the block above each kelp base. When the kelp grows into it, the observer fires a piston that breaks the kelp there. The base survives and grows again.

How many items does a dried kelp block smelt?

Twenty, more than coal or charcoal.

Why did my kelp stop growing?

Either the piston broke the base block, or the plant is not in water source blocks. Kelp also stops at its maximum age if you never cut it back.

Can I bone meal kelp?

Yes. Each use grows it by one block, which is a quick way to test the farm.

Fuel is the input for the automatic smelter. For more simple observer farms, the sugar cane farm and bamboo farm use the same idea.

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