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Fungus in orchid pots

Welcome to the Irish Orchid Society › Forums › Irish Orchid Society Orchid Forums › General Discussion › General Orchid Cultivation Issues, Questions & Advice › Fungus in orchid pots

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  • 4th July 2020 at 10:22 am#2668
    David Morse
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    Hi everyone,

    I am quite new to orchid growing and I have recently gotten some Phalaenopsis and Cattleya orchids. The phals came planted in a bark/ coco chip mix and the Cattleya in spagnum moss. I repotted all of them into a fresh bark mix with a little spagnum moss. I put a little more in moss in the Cattleya to try and avoid transplant shock, I also left behind some of the spagnum as it was so embedded in the roots and I didn’t want to damage the roots. I sprayed hydrogen peroxide 3% on the roots of all the orchids and ran boiling water from the kettle on the mix before potting. I also placed all the pots in boiling water to sterilise them. Each pot has holes punched through the sides.

    I started to notice problems with the Cattleya after a few days as I saw a blue/green mold growing on the roots. I unpotted it and this mold seems to have gotten through the whole root system in little clumps. The roots are not in great shape at all, there are quite a lot of dead roots and brown roots. I took as much of the old spagnum off as I could and sprayed the roots again with hp 3%.

    I have also started to notice some mold growing on the roots of one of the phals and a Zygopetalum i treated reviews for bush snails. This seems to be white mold but one also seems to have a bit of the blue green mold.

    I would really appreciate some advice on this. Is there something I am missing in the potting up process in terms of sterilising everything? Also, what is the best approach to dealing with the mold on the current plants?

    Thanks so much in advance dor your support!

    Kind regards,
    Caroline Muller

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    • 20th July 2020 at 5:48 pm #2673
      David Morse
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      Hi Caroline,
      I am sorry you are having problems. Unfortunately the quality of orchid bark is variable and it is seldom sterile. For that reason I solely use coarse-grade coconut/coir for Cattleyas and Phals. Repotting is stressful to orchids and sometimes they quickly succumb to bacteria/fungi in the new growing media even if the media looks clean and fresh. If you can break up a piece of the bark between your fingers it is probably decaying. Pouring boiling water over the bark would not be enough to kill spores. You are absolutely right to try and remove all the old moss from around the roots. Moss rots after about a year and needs to be changed. New Zealand Sphagnum moss is best but it is expensive and hard to obtain even online. Cattleyas ideally should only be grown in coarse bark/coir with little or no moss as they must have excellent drainage and air around the roots.
      Also it is quite natural to find dead roots when repotting orchids especially Cattleyas providing they are attached to old bulbs. New shoots should have healthy the new roots. Always remove all dead roots at repotting. Personally I feel your orchid media must also be be too wet which has encouraged the mold. If possible I would repot into fresh media obtained from a different source (NEVER use Westland orchid compost, it is dreadful in my experience). Very importantly make sure you do not overpot which could also be contributing to your issue. You could add polystyrene foam chunks as a space filler if you have only a large sized pot. If you have to stick with the current compost then make sure to allow drying out before rewatering the mold should not like that and provide plenty of ventilation on the summer days.
      Perhaps other members can make suggestions? I have not used anti-fungicides. Best of luck and let everyone know what the long term outcome is for your plants.

    • 27th July 2020 at 5:28 pm #2675
      David Morse
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      Hi Shane,

      Thanks so much for all of your advice, I really really appreciate it.

      In the end I unpotted the plants with mold and cut off dead roots that were present and the repotted into fresh bark. I think that I didn’t get all the dead roots in the first repot and that this was the main cause of the problem to be honest. I think that I have managed to address the issue but I won’t speak too soon!

      Kind regards,
      Caroline

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