Kratky Root Rot: Signs, Causes and What to Do

Root rot is the problem that ends the most Kratky crops. It starts below the lid, so the first sign is often a plant that wilts while standing in solution. Knowing what healthy roots look like, and what conditions rot needs, makes it far easier to avoid.

Healthy roots vs rotting roots

What to look for when you lift the lid

	Healthy roots	Root rot
Color	White to cream (can be stained by some nutrients)	Tan, brown or dark brown
Texture	Firm, with fine root hairs	Slimy, soft, outer layer slides off
Smell	Fresh or earthy	Sour, rotten or swampy
Plant above	Upright, growing	Wilting, yellowing, growth stops

What causes root rot in Kratky

Root rot is usually caused by water molds and fungi, such as Pythium, attacking roots that are already stressed. In a Kratky kit the stress almost always comes from a lack of oxygen. A Kratky system has no air pump, so roots get oxygen from two places: the air gap that opens up as the level falls, and the oxygen dissolved in the solution. Root rot follows when either one is lost.

• The air gap was flooded. Topping the reservoir back up to the original line puts the air roots under water. They are adapted to air, and they die and decay. The article on the Kratky air gap explains why the level should fall.
• The solution is warm. Warm water holds less dissolved oxygen than cool water, while warm roots use more. A reservoir in a sunny window or near a heater is at risk.
• Organic matter is rotting in the water. Dead leaves, algae, old roots from a previous crop or a dirty container feed the organisms that cause rot.
• The container was not cleaned between crops, so spores carried over.

What to do if you find root rot

1. Decide if the plant is worth saving. A lettuce close to harvest is better harvested now. Severe rot rarely recovers.
2. Remove the plant and rinse the roots gently in clean, cool water.
3. Trim away brown, slimy roots with clean scissors, keeping any firm white ones.
4. Clean the container thoroughly and mix fresh solution.
5. Set a proper air gap. Fill so only the lower part of the remaining roots sits in solution.
6. Move the kit somewhere cooler and out of direct sun on the reservoir.

Throw away rockwool from a plant with root rot rather than reusing it, and clean the net pot well.

How to prevent root rot in the next crop

• Never refill to the top once air roots have formed. If the plant runs low, add a little solution below the air roots, as the guide on how often to refill a Kratky kit explains.
• Keep the reservoir cool and dark. An opaque container in a spot away from heat helps on both counts.
• Start every crop in a clean container with fresh solution.
• Remove dead leaves that fall onto the lid or into the water.
• Size the container so one fill lasts; see the Kratky containers guide.

Why Kratky kits are prone to it late in a crop

Root rot often shows up in the last weeks rather than the first. By then the plant is large and drinking fast, the root mass is dense, the solution is older and may hold bits of dead root, and growers are most tempted to top the reservoir up. Summer heat adds to the risk. Keeping the refill rule in mind during those final weeks matters more than at any other point, and harvesting a little early is often better than nursing a struggling plant to full size.

Root rot or something else?

Brown roots are not always rot. Some nutrients stain roots tan, and roots that have been in the air gap look different from those in the water. If the roots are firm, smell fresh and the plant is growing, it is probably fine. If the plant wilts in water, the guide to Kratky plant wilting works through the other causes.

Frequently asked questions