Kratky Problems and Fixes
Kratky systems are simple, so when something goes wrong the cause is usually one of a few things: light, the water level, the solution, or temperature. This guide to Kratky problems and fixes works through the most common ones.
Symptoms at a glance
| Symptom | Usual cause | Guide |
|---|---|---|
| Green film, green water | Light on the solution | Algae |
| Brown, slimy, smelly roots | No air gap, warm or dirty water | Root rot |
| Yellow leaves | Nitrogen, pH, light or roots | Yellow leaves |
| Drooping while in solution | Drowned air roots, heat, rot | Wilting |
| Brown, crispy tips or edges | Strong solution, heat, low humidity | Below |
| Long, thin seedlings | Too little light | Below |
| Tall, bitter lettuce | Bolting from heat or long days | Below |
Green film or slime: algae
What you see: green or brown film on the container walls, green water, or slimy coating on roots.
Usual cause: light reaching the nutrient solution. Cover clear containers, close gaps in the lid and cover unused net pot holes.
Full guide: algae in a Kratky kit.
Wilting while standing in water
What you see: leaves droop even though the roots are in solution.
Usual causes: air roots flooded by a refill to the top, warm solution holding little oxygen, root rot, or a reservoir that has run out.
Full guide: Kratky plant wilting.
Brown, slimy, smelly roots: root rot
What you see: roots turn brown, feel slimy and smell unpleasant; the plant wilts and stops growing. Healthy roots are white or cream and smell fresh.
Usual causes: a lost air gap, warm solution, rotting debris in the water or a dirty container.
Full guide: Kratky root rot.
Yellow leaves
What you see: yellowing on older leaves, new leaves, or the whole plant. The pattern points to the cause: older leaves first often means nitrogen, newest leaves with green veins often means high pH, a pale stretched plant means too little light.
Full guide: Kratky yellow leaves.
Brown, crispy leaf tips or edges
Usual causes: solution too strong, very low humidity, heat, or a grow light that is too close. In lettuce, brown tips on inner leaves (tipburn) is often linked to calcium not reaching fast-growing leaves, which heat and fast growth can make worse.
What to do: check the nutrient strength, move the light up if it is close, and keep the growing area from getting too hot.
Leggy, stretched seedlings
Usual cause: not enough light. Seedlings stretch toward a dim light source.
What to do: move to a brighter window or add a grow light, set at the height the manufacturer suggests. See Kratky grow lights.
Plants bolting
What you see: lettuce, cilantro or spinach suddenly shoot up a flower stalk and the leaves turn bitter.
Usual causes: heat and long days. What to do: harvest promptly, keep the growing area cooler, and choose varieties described as slow to bolt.
Solution running out before harvest
Usual cause: the container is too small for the plant or the growth rate. What to do: add solution to a lower level so the air roots stay in air, and use a bigger container next time. See how often to refill a Kratky kit and the Kratky containers guide.
Seedlings not taking off after transplant
Usual cause: the roots cannot reach the solution because the first fill was too low, or the media dried out. What to do: make sure the solution touches the bottom of the net pot at planting, as described in Kratky kit setup.
Pests
Indoor Kratky kits are not immune to pests. Aphids, fungus gnats, thrips and spider mites can all appear. Fungus gnats are drawn to wet media, so keep the top of the media from staying soggy. Check leaf undersides regularly and act early: rinsing pests off, removing badly affected leaves, and using sticky traps for flying insects are common first steps.
Frequently asked questions
What is the most common problem in a Kratky kit?
Algae from light reaching the solution, followed by wilting and root rot from refilling the reservoir to the top.
How do I know my Kratky kit is working?
The plant keeps putting out new leaves, the roots are white and growing down into the solution, and the level falls steadily as the plant drinks.
Should I fix a struggling Kratky plant or start again?
If the roots are healthy, fix the cause and carry on. If the roots are rotten or the plant has bolted, harvest what you can and start fresh in a clean container.
Why are my Kratky roots turning brown?
Brown, slimy roots usually mean root rot, often from warm solution, roots kept fully submerged, or a dirty container. Brown staining from some nutrients is harmless if the roots are firm and smell fresh.
A quick diagnostic order
- Is light reaching the solution?
- Is there an air gap, or was the reservoir refilled to the top?
- Is the solution warm?
- What do the roots look and smell like?
- Was the nutrient mixed at the right strength, and what is the pH?
- Is the plant getting enough light?
Most problems turn up in the first three questions. For the full picture of how a Kratky system should run, start from the Kratky hydroponics guides.