Below is a picture of one of my indoor lemon trees. They are all in self watering pots, and they drink ~3 litre of tap water per week.

What concerns me is the white/orange stuff on the dirt. To the right of the picture have I dug a little bit down, and it seams to only be at the serfuce.


Does anyone know what this is? And how to prevent it?

enter image description here

1 Answer 1


I can't decide whether its just salt deposits or fungal in origin. Either way, it appears to be time to remove any loose soil from the top of the pot, without damaging the roots, and replace with fresh potting compost or whatever it is you use.

If you live in a hardwater area, its more likely to be deposits. You'd be better off not using tapwater, well, at least not straight from the tap. Boil it first and let it cool, or add 2g of citric acid per 10 litres of water and use that, or use rainwater if you can.

I'm assuming there aren't any problems with the plant itself.

  • Yes, I live in an area with very hard water. I'll use your citric acid trick, as I have 5 trees that can hold 4 litre each. The trees are right now attacked by spider mites or something similar that creates sticky webs. =( This time am I spraying them with plant soap, and if I find them again, then I will send a sample to bioproduction.dk so they can find a killer mite for whatever is attacking my trees. Would that also be your advise? May 14, 2015 at 19:10
  • 1
    I'd go for neem oil spray, that should deal with red spider mite - but some people don't like the smell, and as its indoors, that might be an issue.
    – Bamboo
    May 14, 2015 at 19:15
  • I have now ordered 1 Litre of neem oil, but the website doesn't say anything about mixing ratios. What would you recommend? May 16, 2015 at 8:12
  • Just a thought. How can you actually mix oil and water? Normally those two won't mix. May 16, 2015 at 8:41
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    discoverneem.com/neem-oil-spray.html - suggest you read this. You have to add an emulsifier if you're making it up yourself - I've never done it, its not an approved substance in the UK. As I understand it, people usually buy a ready made neem spray.
    – Bamboo
    May 16, 2015 at 10:00

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