The Kratky method is a passive way to grow plants in water. A plant sits in a net cup above a container of nutrient solution, its roots grow down into the solution, and nothing moves: no pump, no air stone, no electricity. As the plant drinks, the water level drops and leaves an air gap, and the upper roots take their oxygen from that air.
Dr. Bernard A. Kratky developed the method at the University of Hawaiʻi at Mānoa. It is best known for lettuce and herbs, which finish on a single fill. Tomatoes are different: they are a long-season crop that drinks far more than one small fill holds, they flower and need pollinating, and they get tall and heavy. Every step below is about growing tomatoes, not lettuce.
How Kratky Tomatoes Differ from Kratky Lettuce
| Lettuce and herbs | Tomatoes | |
|---|---|---|
| Time in the container | Weeks | Months |
| Water use | One fill is often enough | Needs a large reservoir or top-ups |
| Nutrients | One mix for the whole crop | Grow mix, then a bloom mix at flowering |
| Flowers | None needed | Must be pollinated to set fruit (by hand indoors) |
| Support | None | Stakes, cages or strings |
The Steps, in Order
- Pick a variety that fits your space. Micro and dwarf tomatoes fit a shelf; full-size staking tomatoes need room. Compare them on the tomato varieties for Kratky page.
- Choose the container. The bigger the plant, the bigger the reservoir. See Kratky tomato container size.
- Set up the system: lid, net cup, growing medium and solution. See how to set up a Kratky tomato system.
- Mix the nutrient solution with a hydroponic nutrient, then switch to a bloom formula when flowers appear. See Kratky tomato nutrients.
- Check the pH and keep it between 5.5 and 6.5. See Kratky tomato pH.
- Manage the water level. This is where tomatoes differ most from lettuce. See topping up a Kratky tomato reservoir.
- Give it enough light. Indoors that means a grow light on a timer. See grow lights for indoor tomatoes.
- Pollinate the flowers. Indoor plants have no wind or bees. See hand-pollinating indoor tomatoes.
- Prune and support the plant as it grows. See pruning and supporting Kratky tomatoes.
If something goes wrong along the way, the Kratky tomato problems guide lists the common symptoms and what causes them.
What the Kratky Method Does Well for Tomatoes
- No weeding and no soil-borne weeds. The plant grows in water, not a garden bed.
- Indoors, all year. With a grow light, compact varieties fruit through the winter.
- A simple start. Seedlings grown in Kratky are easy to move outside in spring.
- Few parts. A container, a lid, a net cup, a growing medium and nutrients.
What It Does Not Do
Kratky is low-maintenance, not no-maintenance. A full-size tomato still needs its water level checked, a top-up as it drinks, a bloom feed, pollinating indoors, and pruning and support. The method saves you the pump and the weeding, not the gardening.
Frequently Asked Questions
Can you grow tomatoes with the Kratky method?
Yes. Tomatoes grow well in Kratky as long as the container is big enough for the variety and the solution is topped up during the season, because a tomato drinks far more than one small fill holds.
Do Kratky tomatoes need an air pump?
No. The roots get oxygen from the air gap that forms as the water level drops. Adding a pump and air stone turns the system into deep water culture (DWC), which is a different method.
Which tomatoes are easiest to grow with Kratky?
Micro, dwarf and cherry tomatoes are the easiest, because they stay compact, need less water and fruit sooner. Large beefsteak and heirloom tomatoes work too, but need the largest containers and the most support.