DOC №091SEC: SYSTEMSREV: 2026-05-15AUTHORED
Kratky Method — Passive, Pump-less Hydroponics
The Kratky method grows lettuce and herbs in a jar with no pump and no electricity. Cheapest way to start hydroponics, perfect for off-grid and classrooms.
BY ROOTLESS FARM
Quick answer
The Kratky method is passive hydroponics: plant in a net pot through a lid, fill the jar with nutrient solution so the bottom of the cube touches it, and walk away. The plant grows down for water and exposes upper roots to air. A single mason jar of lettuce takes 25 days from transplant.
Why it works
Plants need three things at the root: water, nutrients, and oxygen. Active systems use pumps to oxygenate. Kratky lets the receding water level create an oxygen-rich air gap as the plant drinks.
Build
- Black 1-gallon jar (light blocks algae)
- 2-inch net pot in the lid
- Rockwool cube with seedling
- Mix 1 L nutrient at EC 1.0, pH 6.0
- Fill until cube touches water
Watch out for
- Mosquito larvae in open jars — cover the lid hole.
- Heat: jars above 22 °C breed pythium quickly.
FAQ
3 entries- Q01Is Kratky really pump-less?
- Yes. As the plant drinks, the water level drops, exposing aerial roots which absorb oxygen. The submerged roots feed.
- Q02What crops work in Kratky?
- Lettuce, basil, mint, kale. Avoid heavy fruiting crops — they outgrow the reservoir before harvest.
- Q03How long can I leave it alone?
- Lettuce: 28 days unattended. Basil: top up once at week 4. Larger crops need a one-time refill.