Getting started
The Kratky method in a jar: your first garden without a pump
Functional diagram, not to scale.
An opaque jar, a net pot, a nutrient solution: that's all. The ideal passive method for getting started indoors, even without a balcony.
The Kratky method is the ideal way in: no pump, no electricity for the water, almost no equipment. The plant drinks the solution; as the level drops, it opens an air gap where the upper roots breathe.
What you need
- A glass jar (1 to 2 L, about 1/4 to 1/2 gal), made opaque: a sock, kraft paper, paint. Light makes algae grow.
- A net pot that fits in the opening (or a lid with a hole cut in it).
- A growing medium: rockwool, a coco plug or clay pebbles.
- A complete hydroponic nutrient (often in two parts, A/B).
- Ideally an EC pen and a pH pen.
Set up a Kratky jar
- Sow separatelyIn a rockwool cube or a plug. Only transplant vigorous seedlings, with roots visible below the plug.
- Prepare the solutionIn a pitcher: water, part A, stir, part B, stir. Never mix concentrated A and B together.
- Check EC and pHLettuce: EC 1.2–1.8 mS/cm, pH 6.0–7.0. Basil: EC 1.0–1.6, pH 5.5–6.0.
- FillAt the start, the bottom of the net pot should just touch the solution.
- Put in the seedlingPlug wedged in the net pot, crown above the wet zone.
- Leave the level aloneThat's the principle: let the air gap form. If you top it up, never fill back up to the net pot.
What about light?
Near a bright window in spring and summer; in winter, a small LED grow light above the jar keeps the seedlings from getting leggy. What counts is the total amount of light received per day (DLI), not just the number of hours.
Frequently asked questions
How does the Kratky method work?
The plant uses up the nutrient solution; as the level drops, it opens an air gap where the upper roots breathe, while the lower roots stay in the solution. No pump is needed.
Should you add water to a Kratky jar?
The principle is not to raise the level. If you top it up, never fill back up to the net pot, or the air gap disappears and the roots run short of oxygen.
What plant should I use for my first Kratky jar?
A cut-and-come-again lettuce or basil: short cycle, moderate size, visible results within a few weeks.
