Indoor Growing

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New in 2.1.

Growing hemp under a roof: the Grow Pot, the Hydro Tray and the Grow Lamp, what other lights are worth, how a plant remembers the light it grew under, and everything that can stress a plant indoors. Indoor growing trades the sun's easy-going field for speed, more buds and a room you can pack wall to wall — and it asks for upkeep in return. The basics of planting, trimming and harvesting are on Growing Hemp.

On this page: Quick start · The Grow Pot · The Hydro Tray · How fast, side by side · The Grow Lamp · Other lights · The light record · Stress · Powdery mildew · Automation with dispensers · A sample grow room · Top Shelf

Everything here is the same on Minecraft 26.3, 26.2, 1.21.11 and 1.21.1, on Fabric and on NeoForge, except what is marked Minecraft 26.2 and 26.3. JEI and REI (and EMI on 1.21.1) have an information page for each of the three blocks.

Quick start

1. Craft a Grow Pot, place it, and plant any hemp seeds in it — Beldía too, with no water nearby.
2. Water it with a Water Bottle (on the pot or on the plant) and feed it bone meal — up to three. Watered and fed, it grows half again as fast as the best field.
3. Hang a Grow Lamp above your plants and power it with redstone before they first grow. Every plant in the 3×3 below it harvests two extra buds and an extra leaf.
4. Later, upgrade to Hydro Trays: fill with a water bucket, feed, give it a redstone signal for the pump — twice the speed of the best field.
5. Keep it running. A flowering plant that loses its lamp, sits in a dry bed or a stopped tray, or gets fed or watered twice can stress: fewer buds, seeds in their place, buds that spoil. See Stress.

The Grow Pot

A planter of hemp brick with soil in it, for any strain.

B   B
B D B
  B

B = Hemp Brick · D = Dirt (or any dirt-type block: grass block, coarse dirt, moss…) → Grow Pot

Building Blocks has where hemp bricks come from. A pickaxe breaks it fastest, but anything will.

Soil holds food well and water badly — that is the pot's whole rule.

• Water: one bottle per plant. Use a Water Bottle on the pot — or on the plant, which hands it down to the pot — or let a dispenser do it. You get the glass bottle back, and the soil turns dark like moist farmland. It stays watered until the plant in it ripens, which drinks it. A bucket is refused, and you keep it: buckets are for the Hydro Tray. Rain never waters a pot.
• Don't water a wet pot. A second bottle into soil that is still dark is poured all the same, and has a 1 in 4 chance of stressing a flowering plant in it (the roots sit in water). A ripe plant is safe. Water when the soil looks dry.
• Food: up to three. Bone meal, or anything else in the #c:fertilizers tag, adds one. Compost crumbs on the soil show how much is left, thinning as it goes; a full pot refuses more, and you keep it. Each plant that ripens eats one, so a pot is fed every third plant. Any fertiliser is worth exactly one, however fancy.
• Feed the pot, not the plant. Bone meal on the plant grows the plant instead. With a plant in the pot, aim at the pot's side, or feed it between plants.
• Food only works in water. A dry pot grows like dry farmland however well it is fed.
• No crowding. A plant in a pot has soil of its own, so pots packed wall to wall all grow at full speed — the real reason to pot.
• One stem short. A potted plant's roots are boxed in, and it harvests one Hemp Stem fewer. Breaking the pot under a plant harvests the plant first, with your tool (so Fortune counts).
• It cannot be trampled.
• Picking it up keeps its food, not its water. A freshly crafted pot is dry and empty.
• It works in the Nether. Vanilla's water bottle never boils away, so a pot grows hemp there. Bring the bottles; there is no water to fill them from.

Pot	Grows like	Stress risk while flowering
watered, with food	1.5 × the best field	none
watered, no food	the best field (a lone plant on moist farmland)	none
dry, food or not	dry farmland	1 in 3 each growth step

The Hydro Tray

A deep-water-culture reservoir: an opaque tote, a lid with a net pot of clay pebbles, an air pump on the front and a sight tube showing the water.

C R C
C P C

C = Copper Ingot · R = Redstone Dust · P = Grow Pot → Hydro Tray

Mine it with a pickaxe, or it drops nothing. Its front — the sight tube and the pump — faces you when you place it.

Three things have to be true at once, and each one shows on the block:

1. Water. A Water Bucket fills it to the top and hands back the empty bucket; a full tray refuses the bucket, and you keep it. The sight tube shows the level.
2. Nutrients. Bone meal, or anything in #c:fertilizers, mixed into the water — the tube turns from blue to green. It needs water to go into, and one feed is enough: an empty tray, or a fed one, refuses it.
3. The pump. A redstone signal to the tray — a lever on it, a block of redstone beside it, powered dust running into it. The pump's light comes on and bubbles rise through the clay pebbles. It starts and stops the instant the signal does.

Water	Fed	Pump	Grows like	Stress risk while flowering
yes	yes	on	2 × the best field	none
yes	no	on	the best field — plain water is just a wet bed	none
yes	either	off	the best field	1 in 6 each growth step: still water rots the roots
none	—	—	dry farmland — slower than a field	1 in 3 each growth step

• Each plant that ripens drinks a third of the water, and the nutrients drain away with the last of it. The rhythm is: fill, feed, three plants. Between plants you can top it up with another bucket — it fills to the top and keeps its nutrients.
• It is unforgiving, but nothing ever dies of neglect — the same as farmland in vanilla. Neglect costs time, and a flowering plant's health.
• No crowding, like the pot: trays packed wall to wall grow at full speed. One stem short, like the pot, and breaking the tray under a plant harvests the plant first.
• Picked up, it comes back empty.
• No hydroponics in the Nether. Water boils away there: the tray takes neither bucket nor feed, and the bucket pours and hisses off as it would anywhere in the Nether. Use Grow Pots there.

How fast, side by side

Average time from seed to ripe. Each growth step is a roll, so single plants vary.

	Purple Kush · Beldía	Lemon Haze
Hydro Tray: water, fed, pump on	about 12 min	about 16 min
Grow Pot: watered and fed	about 16 min	about 21 min
Grow Pot watered, no food · Hydro Tray with plain water or the pump off	about 24 min	about 32 min
Field: moist farmland, single rows	about 24 min	about 32 min
Field: moist farmland, packed solid	about 48 min	about 64 min
Dry Grow Pot · empty Hydro Tray	about 56 min	about 72 min

A Grow Lamp overhead shaves a few per cent off any of these (it speeds the young plant up by a tenth). The plants still need light 9 or more at their base to grow at all, as on a field. A server can scale every time with cropGrowthMultiplier (Configuration).

The Grow Lamp

An LED panel hung from the ceiling on two copper chains, with a violet redstone lamp for a face.

C A C
A L A
C A C

C = Copper Ingot · A = Amethyst Shard · L = Redstone Lamp → Grow Lamp

Mine it with a pickaxe, or it drops nothing.

Hanging it. It needs a ceiling — a block with a solid underside — like a hanging lantern, and drops if the ceiling goes.

Powering it. It is a redstone lamp in everything that matters: it lights when it gets a redstone signal and goes out a moment after the signal stops. Put a lever or a button on the ceiling right beside it, run redstone dust over the block it hangs from, or simply hang it from a Block of Redstone to keep it on for good. A powered lamp is hard to see working outdoors in daylight, as any lamp is: look for the lit edge round the panel and the faint violet haze drifting down from it.

Where. Count from the top of the plant as it will be when grown — two blocks for Purple Kush and Beldía, three for Lemon Haze — and hang the lamp in any of the three blocks above that: right on top of the grown plant, or with one or two blocks of air between.

Strain	Space between the bed and the lamp
Purple Kush, Beldía	2, 3 or 4 blocks
Lemon Haze	3, 4 or 5 blocks
A room with both	3 or 4 blocks

Reach. A lit Grow Lamp works for every plant in the 3×3 below it: the one underneath and the eight around. Its light passes through glass and other plants on the way, but an opaque block stops it.

What it gives a plant that grew under it the whole way (see The light record):

• +2 buds and +1 Hemp Leaf at harvest;
• two leaves instead of one every time you trim it — the second is a real extra;
• growth a tenth faster while it is young, before it flowers;
• but charas comes off it at 1 in 8 instead of 1 in 4. Charas is a field craft.

Watch out: In a sealed room the lamp is also the light the plants grow by, and they need light 9 at their base. Hung at the very top of its range over Lemon Haze — five blocks of space — it leaves the four corner plants of its 3×3 at light 8: alive, but not growing. Hang it a block lower, or light the room as well.

Minecraft light has no colour, so a Grow Lamp lights the room white like any lamp; the violet is its face and the haze under it. Shader packs that read LabPBR materials make its face glow violet. JEI and REI give the lamp, the pot and the tray an information page each:

Other lights

Other lights help too, less — and only the plant directly beneath them, within the same three blocks above its grown top.

Over the plant	The plant's record	At harvest
a lit Grow Lamp (reaches the 3×3)	grow lamp	+2 buds, +1 leaf, +1 leaf per trim, faster while young
a lit, switchable lamp at full brightness: a redstone lamp, a copper bulb, most modded lamps	lamp	+1 bud, +1 leaf
any other full-brightness block: glowstone, sea lantern, shroomlight, froglight, lantern, jack o'lantern	ambient	an even chance of +1 bud
torches, end rods, anything dimmer than full brightness; campfires, fire and lava; the sun	nothing	—

"Full brightness" is light level 15. A copper bulb dims as it oxidises (12, 8, then 4) and stops counting — wax it. A plant grown under any of these, the Grow Lamp included, gives charas at 1 in 8 instead of 1 in 4.

For pack makers: #hempdustry:grow_lamps (a block tag) makes another mod's grow light a full Grow Lamp, and #hempdustry:not_grow_lights lists what is bright but never lights a plant. See Tags.

The light record

Every hemp plant keeps a record of the light it grew under, and the harvest reads the record — never the lamp. The game calls it the plant's condition: press F3 and look at a plant to see it among the block's details (natural, ambient, lamp, grow_lamp, or stressed).

When	What the record does
its first growth step (from seed)	takes the best light over it right then. The sun is not a light here, so a plant that sprouts with no lamp over it is a field plant for life
every later step — natural growth, bone meal or a bee's	keeps the weaker of its record and the light over it now. Swap a Grow Lamp for glowstone halfway, and it harvests as glowstone
a step that finds no counted light	if the step leaves the plant below stage 4, it becomes a field plant; if it takes it to stage 4 or beyond — flowering — it is stressed
a field plant, or a stressed one	stays as it is

What that means in practice:

• Hang and power the lamp before you plant, and leave it alone until you harvest.
• Never put a grow room's lamps on a daylight sensor or a timer. A flowering plant that grows one step under no counted light is stressed.
• A lamp moved over a finished plant does nothing, and one lamp cannot be carried from plant to plant: growth steps come at random moments, and any one of them can catch the plant without it.
• Switching off in the dark is a pause, not a stress. In a room with no other light the plants simply stop growing below light 9. But, as with any crop, a plant left below light 8 breaks off the next time a block beside it changes.

A plant with a lamp in its record looks a shade deeper green than a field plant; a stressed one is drawn differently (below).

Stress

A flowering plant — one taking its last four growth steps, to stages 4, 5, 6 and 7 — can be stressed by a bad bed or a lost light. The causes, all on the equipment where you can see them:

Cause	Where	Odds	Over a whole flowering
Losing its light — a growth step with no counted light over a plant that had one	any plant grown under a light	certain	—
A dry bed — a growth step in a pot with no water, or a tray with none	pot, tray	1 in 3 per step	about 4 plants in 5
A stopped pump — a growth step in a tray with water but no signal	tray	1 in 6 per step	about half the plants
Overwatering — a water bottle into a pot that is still wet	pot	1 in 4 per bottle	—
Overfeeding — bone meal on a flowering plant in a bed that already has food	pot with food in it, fed tray	1 in 9 per bone meal that grows it	about 3 in 10 for a plant rushed from stage 4 to ripe with bone meal
Bone-dry farmland — a growth step on farmland that has dried right out	field	1 in 20 per step	about 1 in 5

The rules:

• Only while flowering. Overwatering and overfeeding look at the plant when you do it: before stage 4 it is safe. Feed the bed, not the plant.
• A ripe plant is past all of it. A finished plant waiting for the shears cannot be stressed.
• One roll per step, at the worst odds present — a dry, fed pot under bone meal rolls once, at 1 in 3. A step with nothing wrong rolls nothing.
• Any plant can be stressed, lamp or no lamp. A lamp-grown plant that stresses loses the lamp's extra buds with it — that is the stake indoors.
• Stress is for good. The plant does not recover.

What a stressed plant looks like: its colour drains — Purple Kush's purple fades to a sickly green — its oldest leaves yellow and die back brown, and yellow anthers show among the flowers, which is where its seeds come from.

What it gives:

• one bud fewer than the same plant healthy, and none of a lamp's bonus;
• two extra seeds;
• each bud a 1 in 4 chance of coming off as Schwag — 20%, 15% or 10% with Fortune I, II or III;
• charas at 1 in 8.

Powdery mildew

Minecraft 26.2 and 26.3 only. Stress is not the only way a roofed grow goes wrong. Hemp under a roof (glass included) can catch powdery mildew: about 1 chance in 150 per growth step, white powder on the plant, and a spread to the plants right beside it. A field plant never catches it, and it never kills a plant. At harvest a quarter of a mildewed plant's buds come out as Schwag (20%, 15% or 10% with Fortune I to III). Shears in a trim window clear it, with no leaf; vanilla's potent sulfur under water gives off a gas that keeps plants within 3 blocks clean, but a plant gassed while it flowers is left sulfured and a tenth of its buds turn to schwag. Mildew is not stress, so it costs no bud and gives no seeds. The whole story, and the switch to turn it off: Minecraft 26.x.

Automation with dispensers

A dispenser does for the beds what your hand does, and keeps the empty container.

The dispenser holds	Facing	It
Water Bucket	a Hydro Tray that is not full	fills it, and keeps the empty bucket
Water Bottle	a Grow Pot	waters it, and keeps the glass bottle
Bone meal	a pot with room, or a tray with water that is not yet fed	feeds it
Bone meal	a plant	grows it a stage, as by hand

• A dispenser can face up into a bed from underneath — handy in the middle of a room, where no bed has a free side.
• A dispensed bottle always pours, wet pot or not, so a dispenser on a clock is a drip line that overwaters. Fire it once per plant, after each harvest.
• Fire a bucket dispenser only when the tray needs water: in front of a full tray it does what a bucket does in front of any other block.
• A dispenser feeds a bed with bone meal only; other fertilisers go in by hand.
• A bed has no comparator output.
• Rubbing for charas can never be automated: it is a right-click on a living plant.

Dispensers, a lever or a block of redstone for each pump, and an always-on lamp make a room that needs you only to plant, trim and harvest.

A sample grow room

A Sea of Green — the real hydroponic technique, and the shape the indoor set is built towards: nine Hydro Trays under one Grow Lamp. For Purple Kush or Beldía, from the floor up:

1. Floor: a 3×3 of Blocks of Redstone. They run the nine pumps, for good.
2. On them, nine Hydro Trays, their fronts facing the way you will walk.
3. Two blocks of air above the trays for the plants.
4. The Grow Lamp, above the middle tray — right on top of where the grown plants will be.
5. The ceiling it hangs from: one more Block of Redstone over the lamp keeps it lit for good, or an ordinary block with a lever beside the lamp.

Wall it in with anything and roof it over — glass will do — and creepers never notice it. With the lamp as the room's only light, every plant in the 3×3 is bright enough to grow.

To run it: before planting, fill every tray with a bucket and feed it bone meal (the tubes turn green); then plant. Trim each plant at its last short stage and again just after it shoots up. Harvest; then, with the tray's top free again, top it up with a bucket and feed it if the tube has gone blue, and replant. Each tray holds enough for three plants, so topping up after every harvest means the middle tray, which you can only reach from above, never runs dry.

What it gives: each Purple Kush, trimmed twice, comes off with about six buds (4 + 2 from the lamp, plus the random bonus), four leaves handed over during the trims and about five more at harvest, every twelve minutes or so. Nine of them is a lot of hemp.

For Lemon Haze, add one more block of air (three in all) between the trays and the lamp. To grow more, repeat the 3×3 with one lamp over the middle of each.

Top Shelf

Top Shelf is a goal in the advancement tree, the last of the indoor chain under Hemp Builder: Pothead (place a Grow Pot), then Sea of Green (harvest a plant from a Hydro Tray) and Midnight Sun (harvest a plant grown under a Grow Lamp), then Top Shelf: harvest a fully trimmed plant grown under a Grow Lamp in a Hydro Tray.

How to get it:

1. A Hydro Tray, filled, fed and pumped — a stopped pump or a dry tray can stress the plant, and a stressed plant has lost its lamp.
2. A lit Grow Lamp over it, hung and powered before you plant, and left on until harvest.
3. Plant any strain, and don't bone-meal it once it flowers (the fed tray makes that overfeeding).
4. Trim it twice: at its last one-block stage, and again just after it grows into two blocks.
5. Let it ripen, then break it. Its record must still say grow_lamp — check with F3 if you are unsure.

The other advancements are on Advancements.

See also: Growing Hemp · Strains · Hash and Concentrates · Configuration