GenetixBayEST. 2009
Systems · Beginner · 2 min read

Kratky (passive, non-circulating hydroponics)

Kratky is hydroponics with no pump: the plant sits above a container of nutrient solution, drinks it down, and the growing air gap gives the upper roots oxygen. It was developed and published for lettuce and tomatoes at the University of Hawaii. Cannabis can be grown this way, but its large water use means big containers, careful refills that keep the air gap, and close attention to water temperature and EC drift.

Supported
Draft: awaiting expert review Updated
SeedlingVegFlowerDWC

Being reviewed. Our editors are double-checking a few figures in this article against primary sources. Marked passages may change.

Short answer. Kratky needs no pump, no air stone and no electricity: a net pot sits in a lid over nutrient solution; the plant drinks the level down, and the expanding air gap gives the upper roots oxygen while the lower roots keep drinking [1][2]. It's proven for lettuce and was extended to tomatoes with refills [3]. Cannabis drinks far more than lettuce, so you need large containersbeing reviewed, refills that don't drown the air-root zone, and cool solution.

How it works

At the start the solution touches the bottom of the net pot. As the plant drinks, roots follow the water down; the upper root mass becomes "air roots" in a humid gap. Refilling to the top would submerge those air roots, which are not adapted to anaerobic water, inviting rot [1][3].

Numbers that matter

Parameter Target Notes
Starting level Just touching net pot base [1]
Refill Only partway (e.g. to ~1/2–2/3 of the original level), or with weak solution being reviewed
Solution temperature 18–22 °C (64–72 °F) No aeration = less margin than DWC
pH 5.6–6.2 Drifts up as plants feed
EC Start 0.8–1.4 mS/cm EC often rises as water use outpaces uptake
Container Opaque, light-tight Algae otherwise

How to run it

  1. Best for autoflowers, small photoperiod plants, mothers and clones.
  2. Start with a seedling or rooted clone in a net pot with clay pebbles.
  3. Check level, pH and EC every few days; add plain water if EC climbs fast, weak feed if it falls.
  4. Keep the container cool and dark.
  5. If roots go brown and slimy, convert to DWC with an air stone.

Jardin notes

Jardin method "Kratky (monitor only)": a Root node in monitor mode reads pH/EC/water temperature and level or mass; dosing is disabled in software and channels unmapped, so no actuator can misbehave. Alerts like "EC rising fast, add water" and "water temp 26 °C". Automation level 0. It's the cheapest entry to the data side and the natural path to DWC [4].

Common mistakes

  • Topping up to the brim.
  • Small containers for big photoperiod plants (they drink a 20 L tote in days in flower).
  • Clear containers.

Evidence

The method is Established for lettuce and Supported for tomatoes with refills [1][2][3]. Kratky for cannabis is Grower practice.

Questions this article answers

Can you grow cannabis with the Kratky method?

Kratky is hydroponics with no pump: the plant sits above a container of nutrient solution, drinks it down, and the growing air gap gives the upper roots oxygen. It was developed and published for lettuce and tomatoes at the University of Hawaii. Cannabis can be grown this way, but its large water use means big containers, careful refills that keep the air gap, and close attention to water temperature and EC drift.

How big a Kratky container for cannabis?

Kratky is hydroponics with no pump: the plant sits above a container of nutrient solution, drinks it down, and the growing air gap gives the upper roots oxygen. It was developed and published for lettuce and tomatoes at the University of Hawaii. Cannabis can be grown this way, but its large water use means big containers, careful refills that keep the air gap, and close attention to water temperature and EC drift.

Should I refill a Kratky reservoir to the top?

Kratky is hydroponics with no pump: the plant sits above a container of nutrient solution, drinks it down, and the growing air gap gives the upper roots oxygen. It was developed and published for lettuce and tomatoes at the University of Hawaii. Cannabis can be grown this way, but its large water use means big containers, careful refills that keep the air gap, and close attention to water temperature and EC drift.

Why are my Kratky roots rotting?

Kratky is hydroponics with no pump: the plant sits above a container of nutrient solution, drinks it down, and the growing air gap gives the upper roots oxygen. It was developed and published for lettuce and tomatoes at the University of Hawaii. Cannabis can be grown this way, but its large water use means big containers, careful refills that keep the air gap, and close attention to water temperature and EC drift.

Sources

  1. Kratky BA, 2004. A suspended pot, non-circulating hydroponic method. Acta Horticulturae 648:83–89. ctahr.hawaii.edu/hawaii/downloads/A_Suspended_Pot_Non-circul
  2. Kratky BA, 2009. Three non-circulating hydroponic methods for growing lettuce. Acta Horticulturae 843:65–72. ctahr.hawaii.edu/Hawaii/downloads/Three_Non-circulating_Hydr
  3. Kratky BA, Maehira GT, Cupples RJ, Bernabe CC, 2005. Non-circulating hydroponic methods for growing tomatoes. Proc. National Agricultural Plastics Congress 32:31–36. ctahr.hawaii.edu/Hawaii/downloads/Non-Circulating_Hydroponic
  4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins)..

Related

SupportedIntermediate · Draft

Deep water culture (DWC)

In DWC roots hang in an aerated nutrient solution. It grows fast but depends on two things: dissolved oxygen (keep above about 6 mg/L, ideally near saturation) and solution temperature (18–22 °C / 64–72 °F). Warm, poorly aerated water is how Pythium root rot starts. Run pH 5.6–6.0 and EC 0.8–2.0 mS/cm by stage, and treat the air pump as life support.

Grower practiceBeginner · Draft

Choosing your growing system: soil, coco, rockwool or hydro

Choose by how much attention and measurement you can give, not by yield claims. Soil and living soil forgive mistakes for days; coco and drip need daily feeding; DWC, NFT and aeroponics grow fast but can lose roots within hours if a pump or air supply fails. No controlled study shows one system out-yielding the others when light and climate are equal.

EnvironmentSupportedBeginner · Draft

Temperature by stage: day, night and root-zone targets

Run roughly 24–28 °C (75–82 °F) by day in veg, 22–26 °C (72–79 °F) in flower, cooling to 20–24 °C (68–75 °F) in late flower, with nights 3–6 °C (5–10 °F) cooler. Above about 30 °C (86 °F) photosynthesis in cannabis falls unless light and CO₂ are high. Keep the root zone and hydro reservoirs at 18–22 °C (64–72 °F).

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