Rain water / roof moss question

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Hi All,

I currently get all my rain water from water butts connected to the downpipes from the roof of the house. The roof is so covered in moss we are going to have to get it cleaned to prevent the gutters getting blocked. A couple of the companies we are looking at use a bio-cide to clean the tiles and then apply a coating to the tiles which has a residual effect for 3-4 years to prevent the moss from re-growing/germinating.

Does anyone know if the rain water collected after the treatment is going to harm any of my carnivorous plants (Drosera, Sarrs and VFTs)? At least for a while the moss growth on the growing media won't be as bad...

Many thanks in advance,


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7 minutes ago, gardenofeden said:

Depends what the biocide and coating are, can you ask? 


I have asked the company about it but not had a response. The website for one of the cleaners/biocide they say is used has a COSSH sheet - here is a snippet from it:

  • Hazardous ingredients:


EINECS CAS PBT / WEL CLP Classification Percent

264-151-6 63449-41-2 - Acute Tox. 4: H312; Acute Tox. 4: H302;

Skin Corr. 1B: H314; Aquatic Acute 1:



  • Persistence and degradability: Biodegradable.
  • Bioaccumulative potential: No bioaccumulation potential.
  • Mobility: Readily absorbed into soil.
  • Other adverse effects: Negligible ecotoxicity.

It also mentions that once dry it is safe for wildlife/pets etc. so perhaps after the initial application has dried it breaks down? My A-Level chemistry is a little rusty after 20 years and the above chemical name means nothing to me now... a quick google of EU chemical names suggests it is actually Benzalkonium chloride which breaks down into ammonia, chloride, water and carbon dioxide.... which if it gets diluted in the water butts should be okay for my plants? Might it be worth purging the first collection of rain water just in case? Would the fact that the carnivorous plants are standing in the water and the soil "wet" would that make a difference?

I can't find any info on the sealant though but if it is for waterproofing tiles it must be safe (for plants) otherwise it would gradually dissolve and, I suppose, defeat the purpose of having it in the first place?

Thanks for any insight you can give.

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  • 3 weeks later...

Be careful what they use on your roof - pressure washing can strip the surface layer off roof tiles reducing their life considerably. Many tiles have a lifetime of around 20 years and then need replacing as they start to become porous (see for example Marley website for info). Sometimes it's better to live with the moss and cleaning gutters every year! I'm speaking from painfully learned experience.......

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  • 6 months later...

In response to Dunc, it depends on how much the service you are working with cares for the consequences of their work. I used to order this power washing service. Asked them about any possible damage to the surface layer of the roof tiles and they said that they are aware of the possible consequences and they approach every case differently, depending on the circumstances. The difference is in the service you chose and in asking them these questions. Some do in fact try to save money on these things but there are those whose reputation will not let them do such a thing

Edited by Alexaander
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  • 5 months later...

i have my garden full of vegetables so I didnt want my roof cleaners applying a biocide anywhere near my crops. cant imagine the damage it would do to my beautiful little garden, instead i found a tool on google and i scraped the moss off using that tool (https://roofscraper.co.uk/) and a long pole. ill just scrape the moss off whenever it is needed rather than spraying damaging chemicals.  I also didnt want them pressure washing the roof as ive heard all sorts of nightmares about people using jet washers that are way too powerful for roof cleaning and causing insane amounts of damage to the underlaying of the roof tiles.

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  • 5 months later...

Asking your pressure washing technician ahead of time will prevent any confusion you may have about this issue. Using a power washing technique instead of a soft washing technique may cause damage to your roof. It depends on what kinds of chemicals they use to tell if it will damage your plants when you begin watering them. 

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If it breaks down into ammonia. then that is broken down by bacteria into nitrites which are further converted to nitrates which is essentially plant food. So may harm sensitive carnivorous plants but is great for other plants.

You could test the product on a single sacrificial CP to see the effcts before risking your whole collection

Edited by mantrid
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