Tutorials/Kelp farming

This tutorial seeks to teach you how to farm kelp, which are plants that are naturally found underwater.

Mechanics
Kelp grows similarly to sugar cane. One stem block can be placed underwater, and then it will spontaneously grow upwards until the top of the kelp is one block below the water surface. Also, like Sugar Cane, Bone Meal cannot be used to boost the growth rate of Kelp.

When kelp is planted or the plant above is broken, it sets a random age from 0 to 24. When kelp grows, the grown plant will add 1 to the age from below. If a kelp plant has an age of 25, it will not grow. This means that a kelp plant can grow between 2 and 26 blocks tall.

Kelp has a 14% chance of growing each random tick. This means that there is a 50% chance that the kelp will grow in the first 4.6 ticks, a 75% chance that it will grow within 9.19 ticks, and a 25% chance it will grow later. For information on random tick timings, see block tick.

Based on testing, a 20x20 square of kelp (400) down results in a rough 50% gain over the course of 1 minute, or about 600 kelp. This does not mean that half of the kelp grows 1 block; the random nature of the growth creates a negative logarithmic curve of how many plants reach certain heights. (L shaped curve)

Here is the results from a 256 kelp test over a period of 1 real-life minute (1,200 ticks) All kelp were made to be less than age 20 for the trial, so age did not matter as none grew to 6 tall.

Manual farming
Kelp can be manually farmed by placing kelp underwater, waiting for it to grow and then either breaking the kelp block above the bottom one to allow it to keep growing or breaking the bottom-most kelp block to harvest the entire plant.

An important thing to keep in mind is that a Kelp block will always have a certain age value between 0 and 24. A newly-placed kelp block will have a random age value between 0 and 24 and every time the kelp grows by one block, the age value will also increase by one. If the age value of the top-most kelp block reaches 25, the kelp will stop growing. This age value can be checked by pressing F3.

If the player wants to expand their kelp farm to increase the yield of each harvest, there are all kinds of challenges the player must circumvent, including; reduced light conditions, slower mining times, hindered movement and finally the danger of drowning.

Tools and Equipment
If resources allow that, there are a number of tools the player can utilize to greatly enhance their work efficiency at farming:

Tools

 * A Helmet enchanted with Respiration can be a very valuable asset to have when farming kelp underwater as every level of the enchantment extends the time it takes fo the player's oxygen meter to deplete. At level III, the player can spend a full minute underwater.
 * The enchantment can be combined with potions of Water Breathing for even greater effects.
 * A Turtle Shell Helmet is perhaps the best helmet to use for Kelp farming as it will give the player 10 seconds of Water Breathing when underwater. This can be combined with Respiration to great effect.
 * Boots enchanted with Depth Strider can be helpful for moving around in general, as every level of the enchantment reduces the movement speed penalty inflicted on the player when moving underwater.
 * A Helmet enchanted with Aqua Affinity can be helpful as the enchantment increases mining speed when underwater. Normally, if the player mines anything underwater, the mining time will be doubled. Kelp breaks instantly but if one has to, let's say, clear out more space to expand the farm, Aqua Affinity can come in handy.
 * When working on larger farms, a Trident enchanted with Riptide can be useful for rapid transportation over longer distances as Riptide allows the player to launch themselves forward alongside the Trident, travelling a respectable distances in a very short time.

Potions

 * A Potion of Water Breathing is a great asset to have as it prevents the player's oxygen meter from depleting, completely eliminating the threat of drowning for the duration of the potion.
 * A Turtle Shell Helmet comes with 10 seconds of Water Breathing, which can be combined with Respiration by enchanting the helmet.
 * A Potion of Night Vision, while only a secondary priority, can be of some use as it allows the player to see everything as if it were illuminated by a light level of 15, regardless of what it actually is.

Infrastructure
To help streamline the farming process, the farm itself can be supported by additional constructs to benefit it.


 * It becomes quite dark underwater at greater depths so lighting up the farm and all areas around it with things like Jack 'O Lanterns can go a long way in improving both visibility and reducing the spawning of Drowned. Torches do not work underwater (as they instantly break upon contact with Water) but this can be remedied by converting them into Lanterns (which do not break upon contact with Water).
 * Constructing water-free spaces nearby to allow the player to enter and replenish their oxygen meter, can be of great benefit as it allows one to minimize the risk of drowning damage. Proper use of airlocks and doors will be needed in order to keep the water from flooding said areas.
 * If you like the idea of living underwater, you could build an entire base underwater.
 * A Conduit might just be the holy grail of kelp farming as it will, once activated, apply the Water Breathing status effect to all players underwater within a 32-96-block spherical range, centered on the Conduit and it will also attack hostile mobs within that same range, doubling as a defense system.

Semi-automatic farming
Kelp farming can be semi-automated by using a piston to break the second-to-bottom block, and water current to draw the broken kelp into a hopper.

Automatic farming
Kelp can be automatically farmed by detecting when it grows and then breaking the second-to-bottom block. This can be extended indefinitely upwards because kelp will keep growing until it can no longer do so.

Update: Kelp has a grow limit not only depended on water depth but also its age. You can see this number by pressing F3.