A Kratky tomato system has five parts, and none of them plug in. This page shows how to set up a Kratky tomato system: what each part does and how to put them together, from an empty container to a seedling sitting over its solution.
What You Need
| Item | What it does |
|---|---|
| Opaque container | Holds the nutrient solution and keeps light out, so algae can't grow. Size it to the plant: see Kratky tomato container size. |
| Rigid lid with a hole | Holds the net cup above the solution and carries the plant's weight. |
| Net cup | A slotted cup that holds the seedling and its growing medium and lets roots grow out into the solution. |
| Growing medium | Rockwool, clay pebbles or coco coir. It holds the young plant upright in the net cup. |
| Hydroponic nutrient | Feeds the plant. It must be a hydroponic formula, which includes the micronutrients that soil would supply. See Kratky tomato nutrients. |
| pH test kit or meter | Checks that the solution is in the range tomatoes need. See Kratky tomato pH. |
| A support | A stake, cage or string for later. See pruning and supporting Kratky tomatoes. |
Indoors, add a grow light and a timer: see grow lights for indoor tomatoes.
Setting It Up, Step by Step
- Start the seed in a rockwool cube or starter plug and grow it until roots show through the bottom.
- Clean the container and lid, then cut a hole in the lid that holds the net cup by its rim.
- Mix the nutrient solution in clean water at the strength the label gives for seedlings, then check and adjust the pH.
- Fill the container so the solution just touches the bottom of the net cup. The cube stays moist by wicking, and the roots find the water.
- Place the seedling in the net cup and fill around it with clay pebbles or other medium so it stands upright.
- Fit the lid and cover any gaps so no light reaches the solution.
- Mark the starting water level on the outside of the container. You will want to see how fast it drops.
The First Weeks
As the roots grow down, the water level falls and an air gap opens between the lid and the solution. That gap is the point of the Kratky method: the roots in the gap take oxygen from the air, and the roots below take water and nutrients. Don't top the container back up to the net cup. How and when to refill a tomato, which needs far more water than one fill holds, is covered in topping up a Kratky tomato reservoir.
Back to the Kratky method for tomatoes.
Frequently Asked Questions
How high should the water be when you set up a Kratky tomato?
At the start the solution should just touch the bottom of the net cup, so the seedling's cube can wick water. As the roots grow, let the level fall to open an air gap.
Can you use soil in a Kratky net cup?
No. Soil washes into the solution and clogs the roots. Use an inert medium such as rockwool, clay pebbles or coco coir.
Do you need to start tomato seeds in rockwool?
Rockwool is the most common choice, but any starter plug that holds together in water works. The seedling goes into the system once its roots show through the bottom.