A Kratky garden is a simple way to grow a plant. There is no pump and no electricity.
Kratky Problems
Kratky Root Rot
What Kratky root rot is
Kratky root rot is the most serious problem a Kratky container can have. The roots start to break down and can no longer take up water and nutrients, so the plant wilts and stops growing, even though it is sitting in water. Rot is usually caused by water molds and bacteria that thrive in warm, still water low in oxygen. Water molds such as Pythium are common causes in hydroponics.
The good news is that the conditions that cause it are well known, and most of them are easy to avoid.
Healthy roots vs rotting roots
Healthy: white or cream, firm, with a fresh or earthy smell
Healthy: upper roots in the air gap may be finer and fuzzy with root hairs
Rotting: brown or gray, slimy or mushy to the touch
Rotting: a sour or bad smell from the container
Rotting: the outer layer of the root slides off, leaving a thin string
Some nutrients tint roots slightly, so look at texture and smell as well as color.
Why it happens
Warm water is the most common cause. Warm water holds less dissolved oxygen than cool water, and the organisms that cause rot grow faster in warmth. A container in hot sun, near a heater or in a hot room is at much greater risk.
The second cause is a missing air gap. The Kratky method depends on the water level dropping so the upper roots can breathe from the air. If the container is topped up to the brim, those air roots drown. Other causes include light and algae in the solution, dead plant material left in the water, and containers reused without cleaning.
Signs to watch for
The first sign is often above the water: a plant that wilts during the day even though its roots reach the solution, or new growth that stops. Lift the lid and look at and smell the roots. Catching rot early gives you more options.
What to do if you find it
For a small, fast-growing plant like lettuce, starting over is usually the quickest and most reliable fix. Discard the plant and solution, wash the container, lid and net pot in hot soapy water, rinse well, and replant in fresh solution in a cooler spot.
If the rot is mild and only a few roots are affected, you can try moving the container somewhere cooler, making sure there is a clear air gap, and replacing the solution with fresh, cool nutrient water mixed at the label rate. Trim away clearly dead roots with clean scissors. If the plant keeps wilting or more roots turn brown, start over.
How to prevent root rot
Keep the container in a spot that is comfortable for people, out of hot afternoon sun
Fill only to the bottom of the net pot at the start
Let the level drop, and never top up to the brim
Use a dark container and lid so no light reaches the water
Root rot is more common in summer. In hot weather, move containers away from windows that get strong afternoon sun, choose larger containers (more water warms more slowly), and avoid dark containers sitting in direct sun, which absorb heat. Lettuce and other cool-season greens are especially sensitive to warm water; Best Plants for Kratky suggests plants for warmer homes.
Kratky root rot and topping up
If a plant is drinking faster than expected and the roots will lose the water before harvest, top up only a little, so the lower roots reach the solution again but the upper roots stay in air. Adding too much at once is a common way to bring on rot. More in Step 4: Check the water level.
Related problems
Root rot often appears alongside algae, because both are encouraged by light, warmth and stagnant water. See Algae in a Kratky Container and the full list on Kratky Problems.
Choosing plants for warm homes
Some plants tolerate warmth better than others. Basil enjoys warm rooms, while lettuce and spinach prefer cooler ones. If your home runs warm, matching the plant to the room is one of the simplest ways to avoid root rot, and it often gives better leaves too.
Clean tools and hands
Use clean scissors when trimming roots or harvesting, and wash your hands before handling roots. Organisms that cause rot can travel from one container to another on tools, hands and reused net pots, so cleaning between containers helps keep a problem in one jar from spreading.
Tip: If you are unsure whether roots are healthy, smell them. Healthy roots smell fresh; rot smells sour.
