Short answer: for a head of lettuce, plan on roughly 1 to 1.5 gallons of solution from seed to harvest (UF/IFAS). Larger, longer-lived plants need much more, and fruiting crops usually need topping up along the way.
Why volume matters
The Kratky method works best when all the solution is added before planting and the plant is harvested before it runs out (Kratky, 2009). If the container is too small, you have to add solution partway through, which risks drowning the air roots.
Leafy greens
- Lettuce and similar greens: about 1 to 1.5 gallons per plant (UF/IFAS)
- Kratky’s simplest trial grew one lettuce plant in a darkened 4-liter (about 1 gallon) bottle (Kratky, 2009)
- Leafy greens are usually ready 30 to 45 days after planting (UC Master Gardeners, UC ANR)
Herbs
Herbs harvested repeatedly stay in the container for months. Give them more volume than lettuce, or expect to top up carefully.
Fruiting crops
Tomatoes, peppers and cucumbers grow for months and use far more water. UC Master Gardeners note that they usually need the solution replenished over time. Use the largest container practical and plan for regular, small top-ups.
Sizing a container
- Wider containers are better than taller ones, so roots can reach the solution as it drops (UF/IFAS).
- One plant per container is easiest to manage. If several plants share one, multiply the volume.
- Warm weather and strong light increase water use, so allow extra in summer.
Running low?
Measure the EC of what is left, top up with plain water or fresh solution depending on the reading, and keep the new level below the air roots.
Related guide: topping up and replacing Kratky nutrient solution.
Sources
- University of Florida IFAS Extension. Set It and Forget It Hydroponics (HS1488).
- Kratky, B.A. (2009). Three non-circulating hydroponic methods for growing lettuce. Acta Horticulturae 843: 65–72.
- UC Master Gardeners of Orange County, UC ANR. Kratky Hydroponics: Soil-Free Growing Method.
