The Kratky method is one of the simplest ways to grow plants in water. There are no pumps, air stones or timers. A plant sits in a net pot above a container of nutrient solution, and as it drinks, the water level drops and leaves an air gap where roots can breathe. It was developed for leafy greens, but many home growers have tried it with cannabis, especially small autoflowers. This guide explains how Kratky works, how to set one up for cannabis, the challenges and who it suits. It is written for adults 21 and older growing where home cultivation is legal.

How Kratky works

Kratky is a passive hydroponic method. You fill a container with nutrient solution and place a plant in a net pot so the bottom of the pot touches the water. As the plant grows, it drinks the solution and the level falls. Roots grow down to follow the water, and the upper roots sit in the humid air gap, where they take in oxygen. Because nothing moves, there is no power use and no noise.

Why it is tricky with cannabis

Leafy greens need little water and finish fast. Cannabis is a large, thirsty plant, especially in flower. A single photoperiod plant can drink a lot of water each week, so a pure Kratky setup needs a big container or regular top ups. Many growers use a modified Kratky approach, topping up the solution at planned points while keeping an air gap.

That is why small autoflowers are often the best fit. They stay compact and finish in a few months.

What you need

• A lightproof container, such as an opaque tote or bucket
• A lid with a hole for a net pot
• A net pot and a growing medium such as clay pebbles or rockwool
• Hydroponic nutrients made for cannabis or general hydro use
• A pH meter or test kit
• An EC or PPM meter, if possible
• A grow light and a tent or cabinet

Setting it up

1. Prepare the container. Make sure no light gets in, since light grows algae.
2. Mix the solution. Start at a mild strength for seedlings. Adjust pH to the hydro range, often around 5.5 to 6.5. Our guide to pH explains why.
3. Fill the container. Fill so the base of the net pot touches the solution.
4. Start the seedling. Germinate the seed first. Our guide on how to germinate cannabis seeds helps. Place it in rockwool or clay pebbles in the net pot.
5. Set the light. Use a gentle light schedule for seedlings. Our seedling light schedule guide has details.

Managing the air gap

The air gap is what makes Kratky work. As roots grow, the water level should drop a little below the top of the root mass, leaving roots above the water exposed to humid air. If you top up, avoid filling the container back to the brim, since that can drown the upper roots. Many growers top up to about halfway or less, depending on root growth.

Feeding through the grow

Seedlings need light feeding. As plants grow, they need stronger solution. In flower, switch to a bloom formula. With Kratky, the solution changes as the plant drinks, so check pH and strength when you top up. Some growers fully replace the solution once or twice during the grow to avoid buildup.

Temperature matters

Warm water holds less oxygen and invites root rot. Aim to keep the solution cool, often below about 72 degrees. Keep the container off warm floors and out of direct light from the lamp. A cooler room helps.

Common problems

Problem	Likely cause	What to try
Brown, slimy roots	Warm water, low oxygen	Cooler solution, larger air gap
Algae	Light leaks	Cover container fully
Wilting	Water level too low	Top up carefully
Burnt tips	Solution too strong	Dilute or replace

Strain choice

Short, fast autoflowers fit Kratky best. Our autoflower seeds include compact options. Photoperiod plants can work, but they need larger containers and more top ups, and they are harder to keep small.

Training in Kratky

Plants grow fast in water. Gentle low stress training keeps autoflowers short and spreads the canopy under the light. Avoid heavy stress on autoflowers.

Light and environment

Kratky only covers the roots. You still need good light and airflow. Our guide to grow lights for cannabis explains light choice, and our inline fan CFM guide helps size ventilation. Keep humidity in check in flower to avoid mold.

Harvest and cleanup

Harvest when trichomes reach your target. After harvest, empty and clean the container, net pot and lid with a mild cleaner before the next run. Our drying temperature and humidity guide covers drying.

Sizing the container

Container size is the biggest decision in a cannabis Kratky setup. A small autoflower may drink a few gallons over its life, while a larger plant can drink several times that. Bigger containers hold more solution, which means fewer top ups and more stable pH and strength. They also take more room in the tent. Many home growers use a tote or bucket in the range of about 5 to 20 gallons for a single plant. Mark the water level on the outside of the container each week so you can see how fast your plant drinks and plan top ups before the roots run dry.

Is Kratky right for you?

Kratky suits growers who want a simple, quiet, low power hydro setup and are willing to watch water levels. It works best with small autoflowers in a small space. If you plan large photoperiod plants, a deep water culture system with an air pump is often easier to manage.

Final thoughts

The Kratky method strips hydroponics down to a container, a lid, a net pot and nutrient solution. With cannabis, the key is managing the air gap, topping up carefully, keeping water cool and choosing compact genetics. Start with one small autoflower and learn how your plant drinks before scaling up.

Grow legally and responsibly

Home cultivation is only legal in some states, and each state sets its own plant limits, locking rules and rules about whether plants can be visible from a public place. You must be 21 or older to buy seeds from Kind Seed Co, and you should grow only where your state and city allow it. Check your state rules in our guide to the legal requirements for growing weed plants in your state before you plant. Federal treatment of cannabis seeds is also changing, so read our December 11 2026 seed rule explainer before you order. Keep plants and harvested flower locked away from children, pets and visitors, and never drive after using cannabis. This article is general information about gardening. It is not legal advice and it is not medical advice.

Frequently asked questions

Can you grow cannabis with the Kratky method?

Yes, especially small autoflowers. Large photoperiod plants need big containers and regular top ups.

Does Kratky need an air pump?

No. Roots get oxygen from the air gap that forms as the water level drops.

How often should I top up a Kratky container?

It depends on plant size. Top up only part way so an air gap remains for the upper roots.

What pH is used for Kratky cannabis?

Many hydro growers aim for around 5.5 to 6.5.

Ready to start

Browse the full range in the Kind Seed Co shop or go straight to autoflower seeds. Kind Seed Co sells only to adults 21 and older. Always follow the home grow laws where you live.