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.

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 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 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.
 * Boots enchanted with Depth Strider can be helpful for moving around in general, as ever level of the enchantment reduces the movement speed penalty inflicted on the player when moving underground.
 * 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 was 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.
 * Constructing water-free spaces nearby to replenish one's oxygen meter, can be of great benefit as it allows one to minimize the risk of drowning damage.
 * 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 if 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 defined by water depth but by a number. You can see this number by pressing F3.