The Kratky method: passive hydroponics for beginners

The Kratky method is the simplest possible way into hydroponics. As a quick answer: it is passive hydroponics with no pump, air stone, or electricity; a plant sits in a net pot above a sealed container of nutrient solution, and as it drinks, the falling water level leaves an air gap that keeps the roots oxygenated. It is perfect for lettuce, greens, and herbs. If nutrients are new to you, start with hydroponic nutrient basics.

How the Kratky method works

You fill a container with nutrient solution, suspend a net pot so the bottom just touches the liquid, and plant a seedling in growing media. Two things happen as the plant grows:

1. The roots grow down into the solution and drink it.
2. The water level drops, leaving an air gap between the surface and the net pot.

That air gap is the clever part. The lower roots take up water and nutrients, while the upper roots sit in moist air and take up oxygen. No pump is needed because the plant creates its own oxygen zone.

What you need

• A container (a jar, tub, or bucket) ideally opaque to limit algae.
• A net pot and a lid or cover to hold it.
• Growing media (rockwool or clay pebbles) and a seedling.
• Nutrient solution mixed to the crop’s target, following how to mix hydroponic nutrients.

Best crops, and what to avoid

Kratky shines with crops that finish before the reservoir runs out: lettuce, leafy greens, and herbs. For those, mix the solution once (for example, the lettuce EC and pH targets) and largely leave it alone. It is not suited to large, long-season fruiting crops like tomatoes, which drink too much, need topping up, and demand more oxygen than a passive jar provides.

Limits to know

• No top-offs by design. Classic Kratky finishes as the solution is used; topping off too much removes the air gap and can drown roots.
• Algae and heat. Use an opaque container and keep it out of hot, bright spots on the reservoir itself.
• It does not scale easily. For more plants or longer crops, an active system is better; compare them in NFT vs DWC vs Kratky.