I got an email from a worried man who had a complete failure in his rooting efforts. After successfully rooting a variety of plants, he lifted the hood one day to find disaster. Every cutting in the 2’x 2’ box was flat on the surface of the rooting medium, its stem darkened at its base. His setup sounded good: a deep rigid plastic box with drainage and a removable hood made of PVC pipe covered with sheet plastic. He used a heating mat in winter, always waters with distilled water, and ventilates daily. The box sits on a protected porch in USDA Zone 9, the subtropics, so freezing is not a problem. The list of plants he propagated this way was impressive, too, from succulents and green stemmed tropicals to azaleas. He feared he had lost his touch, but I was able to assure him that no existential crisis loomed. The problem was a fungus, probably Pythium, an advantageous soil-dwelling rascal that can destroy vulnerable plant material overnight.
There are so many fungi on Earth that even mycologists can only estimate the number at about 1.5 million species. When I answer questions about a filmy black deposit on tree leaves in summer, it can be painful to explain that the sooty mold fungus is everywhere. Fungi live where they can find a comfortable host, in this case the excrement from insects feeding higher up in the plant. The pH and sugar content of this ‘honeydew’ is perfect for the sooty mold to land in and grow. It is ubiquitous in the atmosphere of humid climates, but some type of fungus is equally present almost everywhere. We depend on many fungi and fight off others like those that caused the disaster for the worried man.
How the fungus got into the rooting chamber is difficult to pin down, as there unfortunately are several possibilities. The good news is that the situation is controllable and preventable with better practices. Once introduced, the fungus proliferates to fill cells and block the progress of water and nutrients from the roots upward. The cutting falls over quickly as its stem stops functioning and by then it is too late to figure out how it happened. The answer to my correspondent’s issue is sanitation to get rid of the pests and keep them away. Even though I know the drill, so to speak, I learned a thing or two as I answered the question – that’s the way it’s supposed to work after all – and wanted to blog about it.
In this case, I think the fungus got into the rooting chamber and took over because good sanitation practices were not followed. To undo the infection is not impossible, but sometimes the easier path is to set up a new rooting chamber and follow these tips:
- Construct your propagation box or chamber from new materials and avoid wood if possible because it is difficult to keep clean.
- Use clean, fresh rooting media and keep extra media clean. Why don’t more bags have zipper closures, anyway? Keep bags of media or its components closed tight or even better, put bags into plastic boxes with tight-fitting tops.
- Love that shop-vac! Keep the area around the rooting chamber clean and dust free to reduce sources of infection and improve air quality for you. If other plants, pots, or soil are nearby, move them.
- Keep a spray bottle of 70% alcohol handy to disinfect any tools used inside the chamber such as misters or watering cans. Be sure any rags or paper toweling you use is fresh, too.
- Clean hands, please. Since it is hard to remember, keep hand sanitizer nearby.
- After each set of clones is rooted and pulled out, clean and disinfect thoroughly.
- Recycle the rooting media into other potting mixes and replace it with new material.
- Wash each component of the rooting box or chamber with soapy water, rinse with clear water, and let dry completely.
- Mix a solution of 1 part chlorine bleach to 9 parts water, put on safety gloves and glasses and disinfect every part of the setup. Prepare only what you can use – bleach loses half its effectiveness in 2 hours.
- To disinfect best is to separate the parts and soak them for 30 minutes in the bleach solution, then rinse in clean water. If your rooting box is indoors, move it into a well-ventilated area before using bleach!
- Use new pots and sheet plastic for each new set of clones. Yes, you can clean them, but besides the rooting media itself, these are the greatest potential sources of contamination.
One more note: Professional products to disinfect include quaternary ammonium compounds (Green-Shield), hydrogen dioxide (Zero Tol 2.0), hydrogen peroxide compounds (Sanidate) and others. When you make the move from backyard propagator to professional and/or greatly increase the size of your propagation operation, consider them. Some organic disinfectants are available; consult product labels and omri.org for details and keep abreast of local restrictions if you are cloning for the organic market.