Root rot shows as brown, slimy roots, a sour smell and a plant that wilts while sitting in water. It is caused by roots running short of oxygen. A plant caught early can usually be saved.
How to Recognize It
- Roots are brown or gray and slimy, and pull apart easily. Healthy roots are white to cream and firm.
- The solution smells sour or swampy.
- Leaves wilt in the heat of the day and do not recover with more water.
- Growth stalls and older leaves yellow.
Roots stained tan by nutrients but still firm and odorless are not rotting.
What Causes It
- No air gap. Refilling to the brim submerges the roots that were breathing air.
- Warm solution. Warm water holds less oxygen and favors the organisms that cause rot.
- Old solution left unchanged for too long.
- Light leaks, which feed algae that then die and decay.
- Soil or dead plant material left in the container.
How to Save the Plant
- Lift the plant out and rinse the roots under cool running water.
- Trim away every brown, soft root with clean scissors, back to firm white tissue.
- Empty the container and scrub it, the lid and the net cup.
- Refill with fresh solution at reduced strength, to a lower level than before, so a good part of the root mass hangs in air.
- Move the container somewhere cooler and out of direct sun on the container itself.
New white roots within a week or two mean the plant is recovering. If the crown itself is brown and soft, the plant is unlikely to survive.
Preventing It
Leave an air gap at every top-up, keep the container cool and lightproof, and change the solution every few weeks. Those three habits prevent nearly all root rot in passive hydroponics.
Related guide: Kratky strawberry problems.
