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What's this yellow stuff on my indoor plant pot?

Just noticed these yellow-coloured stuff on the rim of my white clay plant pot (has a small fern in it). Wondering if anyone knows what it is pls? Thanks


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  • bédébédé Posts: 3,070
    edited January 2023
    Number one advice is: don't let your plant stand in water (even a fern); always empty any cache-pot, quickly.

    The "stuff" is hardness salts from the water aka calcium carbonate.  The "yellow colour" comes from whatever is the compost for the fern.  Probably iron salts.  A good clean-up wouldn't go amiss.
     location: Surrey Hills, England, ex-woodland acidic sand.
    "Have nothing in your garden that you don't know to be useful, or believe to be beautiful."
  • JennyJJennyJ Posts: 10,417
    I get something similar sometimes, but around the inside rim of the plastic plant pots. I think it's mostly limescale from the water, with stuff that's leached out of the compost.
    Doncaster, South Yorkshire. Soil type: sandy, well-drained
  • PlantmindedPlantminded Posts: 3,439
    Using rainwater or filtered water can reduce this problem, try a Brita filter or similar but use cheaper compatible cartridges!
    Wirral. Sandy, free draining soil.


  • JennyJJennyJ Posts: 10,417
    I filter water for the kettle and for drinking, but it's take forever to water all my plants if I had to keep waiting for water to run through the filter! I don't particularly see it as a problem. I just scrape it off from time to time if it bothers me.
    Doncaster, South Yorkshire. Soil type: sandy, well-drained
  • Thanks all! Yes I already use Brita filtered water to water my plants. I usually get the first jug of water in the morning from the tap (stagnating water sitting in the pipes overnight) to water the plants, then get another new jug for drinking water.
  • PlantmindedPlantminded Posts: 3,439
    You must have a lot of houseplants @JennyJ!  I've just watered all mine this morning and only had to refill the 2 litre filter jug once, after watering 5 plants.  The build up of salts in the compost can become problematic for some plants, especially if they are not repotted when necessary.  There was a discussion here recently about flushing out the salts in houseplant compost regularly. @Pete.8 may recall this, I seem to remember him commenting.
    Wirral. Sandy, free draining soil.


  • JennyJJennyJ Posts: 10,417
    edited January 2023
    Somewhere around 30 I suppose (I haven't counted). I propagate sometimes, so there are multiples. All my windowsills are full except the one that I use for seed-raising in spring. I use big plant pot saucers for watering so that the water can run through, and occasionally they get stood in the bath for a good shower and flushing (not all at once obviously!)
    Doncaster, South Yorkshire. Soil type: sandy, well-drained
  • PlantmindedPlantminded Posts: 3,439
    Ah, yes, I now see how it would be a time consuming task for you @JennyJ!
    Wirral. Sandy, free draining soil.


  • bédébédé Posts: 3,070
    edited January 2023
    ** Brita filters just swap calcium for sodium.  Gets rid of limescale, but not the best thing for plants.  **  I water everything with fresh tap water, no problems, but use room temperature rain water for my orchids.  My lemon and oleanders get a good rinse through with rain water in the spring.

    Distilled/deionised water from a clothes dryer or a dehumidifier would be the next best thing.

    By the way, I noticed on a vegan soup that added water (the main ingredient) was not counted as "organic".  Brita-water must be even less organic.

    **Correction: from google:
     activated carbon filters don't remove all nitrates, dissolved minerals, or bacteria and viruses 
    So they don't remove salts, like calcium hardness salts.  Sorry for my earlier misinformation.
    But what do they remove?  Chlorine perhaps, but doesn't boiling achieve that? Or is it just middle-class Angst?
     location: Surrey Hills, England, ex-woodland acidic sand.
    "Have nothing in your garden that you don't know to be useful, or believe to be beautiful."
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