In the Kratky method the container is the plant's whole water supply. Nothing pumps fresh solution in, so the size of the container decides how long the plant can go between top-ups. A tomato is a long-season plant that drinks more every week as it grows and starts to fruit, which makes container size the first decision for a Kratky tomato, not an afterthought.
Match the Container to the Plant
The table below gives common starting points. Bigger is always easier: a larger reservoir holds more water, keeps a steadier temperature and needs fewer top-ups.
| Tomato type | Typical plant size | Container to start with | Where it grows best |
|---|---|---|---|
| Micro tomatoes | Under about a foot | 1 quart to half-gallon jar | A shelf under a grow light |
| Dwarf tomatoes | 2 to 4 feet | 3 to 5 gallon bucket | Indoors or a patio |
| Determinate (bush) tomatoes, such as Roma | 3 to 4 feet | 5 gallon bucket or larger | Outdoors, or indoors with strong light |
| Indeterminate (vining) tomatoes, such as cherry and beefsteak | 6 feet or more | 10 gallon tote or larger | Outdoors or a greenhouse |
A smaller container than this can still work, but it means topping up more often, and on a hot day a small container can run low faster than you expect.
What Makes a Good Kratky Tomato Container
- Opaque. Light reaching the solution grows algae. Use a dark tote or bucket, or wrap a clear jar.
- A rigid lid. The lid holds the net cup and carries the weight of a fruiting plant, so it must not sag.
- Food-safe plastic or glass. The solution sits in it for months.
- Wide rather than deep for big plants. A wide tote leaves room for a large root mass and makes it easier to see the water level.
- Somewhere to anchor a support. Tall tomatoes need a stake, cage or string, and the container has no soil to hold one. See pruning and supporting Kratky tomatoes.
Why Size Matters More for Tomatoes Than Lettuce
A head of lettuce finishes on one fill. A tomato keeps growing for months, and once it is fruiting it can drink a quart or more a day in warm weather. A larger container doesn't remove the need to top up, but it spreads top-ups further apart and makes them less risky. How to refill without harming the roots is covered in topping up a Kratky tomato reservoir.
Once you have the container, here's how to set up a Kratky tomato system, step by step.
Back to the Kratky method for tomatoes.
Frequently Asked Questions
Can you grow a tomato in a mason jar with the Kratky method?
Yes, if it is a micro tomato. A quart or half-gallon jar suits a micro variety on a shelf. A full-size tomato will drink a jar dry in a day or two once it is fruiting.
What size container does a full-size tomato need for Kratky?
A vining (indeterminate) tomato such as a cherry or beefsteak is easiest in a 10 gallon tote or larger. Smaller containers work only if you top up often.
Does the container need to be dark?
Yes. Light on the nutrient solution grows algae, which competes with the roots for oxygen and nutrients. Use an opaque container or cover a clear one.