pure pumice?

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HaoBao
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Re: pure pumice?

Post by HaoBao » Sat Feb 27, 2021 10:32 pm

yonnoy wrote:
Mon Feb 22, 2021 1:08 am
Did you have problems growing cacti and succulent generes with pure pumice? I mean, South American generes need more acid PH substrate (more organic components).
I'd be interested to know more about this too, I've seen it mentioned about North and South American cacti requiring different treatment but never seen any results except in this PDF https://cactiguide.com/pdf_docs/hexalog-engl.pdf where they show a Turbinicarpus growing in different ways because of limestone being added.

https://www.inaturalist.org/taxa/182416-Turbinicarpus

I also don't know how or if it would relate to echeveria as they spread from North to South

https://www.inaturalist.org/taxa/153990-Echeveria
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All my plants are kept indoors and I started collecting in August 2018. Favourites are Pachyphytum, Echeveria, Haworthia, Mesembs and oddball Cacti.
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Re: pure pumice?

Post by Chris L » Sat Mar 27, 2021 11:39 am

I've been trying to get some small pumice (from Germany) for the seedlings and they are not shipping to the UK at the moment. Am now transfering the plants in the German pumice to pots containing larger pumice so I can use the German pumice for my seedlings.

The German pumice isn't any good for adult plants as the slightest knock to the pot and the stuff flies everywhere.

A question I have is this, please?

How much feed would be best for watering into the pumice please? I normally use Chempak 4 and 8. Does anything else need adding, sometimes I've added a little vinegar and Epsom Salts.
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Re: pure pumice?

Post by gerald » Sat Mar 27, 2021 9:52 pm

Chris L wrote:
Sat Mar 27, 2021 11:39 am
How much feed would be best for watering into the pumice please? I normally use Chempak 4 and 8. Does anything else need adding, sometimes I've added a little vinegar and Epsom Salts.
Both Chempak 4 and 8 have trace elements so no need to add anything else.

Don't add Epsom salts or anything else for that matter because you will cause a salt imbalance which could be toxic. In this case too much Epsom salts (magnesium) means the plant will have a hard time taking up calcium.

You're better off giving a low dose of feed (say 50% strength) with every watering. As mentioned earlier, it's also important to acidify the water to about 6.0 - 6.5.

Use a proper pH meter if you can, the cheap test kits are useless. Vinegar will do it but so will citric acid which is easy to find and very cheap.
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Re: pure pumice?

Post by Pattock » Sat Mar 27, 2021 11:03 pm

gerald wrote:
Sat Mar 27, 2021 9:52 pm
Both Chempak 4 and 8 have trace elements so no need to add anything else.
Chempak 8 contains no calcium at all. It is probably designed to use with John Innes and other soils that have ground chalk or limestone added. They sell a soluble calcium supplement as well, probably calcium nitrate but they wouldn't tell me.

Have a look on the side of the box for Chempak 4.

The actual elements in your pumice probably vary depending on the volcano that produced it. Here is a typical analysis of a pumice. https://www.srilava.com/pumice-stone/?lang=en There is plenty of calcium but it is probably as the silicate, which will only leach out into the rhizosphere very slowly compared to the carbonates. The aluminium and titanium are not so good for the plants, hopefully they are also as silicates. Though I think alumina does not get soluble until you get down to about pH 4.

Note the sodium content, which is why you should soak and rinse your pumice very carefully with abundant water before use. Unless you are growing a halophyte.
gerald wrote:
Sat Mar 27, 2021 9:52 pm
Don't add Epsom salts or anything else for that matter because you will cause a salt imbalance which could be toxic. In this case too much Epsom salts (magnesium) means the plant will have a hard time taking up calcium.
As Chempak just have "Also contains Magnesium." on the packet it is, unfortunately, impossible to know how to adjust for different plants that may have requirements for extra magnesium.

gerald wrote:
Sat Mar 27, 2021 9:52 pm
You're better off giving a low dose of feed (say 50% strength) with every watering.
I definitely agree with that, five meals a day rather than one huge supper.

gerald wrote:
Sat Mar 27, 2021 9:52 pm
Use a proper pH meter if you can, the cheap test kits are useless. Vinegar will do it but so will citric acid which is easy to find and very cheap.
Bromothymol blue liquid (usually sold as pH 6.0 to 7.6) is good enough for me and does not need £60, regular cleaning, calibrating nor batteries. Clear results but should be read in natural light. The Chempak should adjust most waters to the correct pH.


What a shame Mount Etna is in Europe. The councils in Sicily have a huge pumice waste problem at the moment. https://www.bbc.co.uk/news/world-europe-56344311
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Re: pure pumice?

Post by Chris L » Sun Mar 28, 2021 11:00 am

Thanks for the information.

Normally I put a scoop of fertiliser in a 2 gallon bucket of water (sometimes a bit more - it is never exact.....). That is what the packet says for frequent use. The normal strength is two scoops per gallon. Does the former sound about right?

Can anything be done about the sodium if plants are in situ. I know I should wash the "stony" part of a mix but I always have to be careful what I am flushing down the drain. [it has blocked in the past....]
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Re: pure pumice?

Post by Pattock » Sun Mar 28, 2021 12:43 pm

I only just got a bag of pumice a few weeks ago and have not had to pot anything up yet. So, I have no idea about its properties yet. I imagine the sodium will wash out pretty quickly with every watering.

If you have asparagus, spinach, callaloo (Amaranthus) or beetroot in the garden they like a bit of salty water and it keeps the weeds down.
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Re: pure pumice?

Post by Chris L » Sun Mar 28, 2021 1:36 pm

Pattock wrote:
Sun Mar 28, 2021 12:43 pm
I only just got a bag of pumice a few weeks ago and have not had to pot anything up yet. So, I have no idea about its properties yet. I imagine the sodium will wash out pretty quickly with every watering.

If you have asparagus, spinach, callaloo (Amaranthus) or beetroot in the garden they like a bit of salty water and it keeps the weeds down.
Thanks, thats good to know that it will wash out.

I cannot remember if it is mentioned up thread, but I've potted everything into pumice to try and get things to dry out quicker - some pots were staying very wet - and I had so many different mixes on the go some pots weren't actually getting wet at all. No consistancy at all.
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Re: pure pumice?

Post by gerald » Sun Mar 28, 2021 8:19 pm

Pattock wrote:
Sat Mar 27, 2021 11:03 pm
gerald wrote:
Sat Mar 27, 2021 9:52 pm
Both Chempak 4 and 8 have trace elements so no need to add anything else.
Chempak 8 contains no calcium at all. It is probably designed to use with John Innes and other soils that have ground chalk or limestone added. They sell a soluble calcium supplement as well, probably calcium nitrate but they wouldn't tell me.

Have a look on the side of the box for Chempak 4.

The actual elements in your pumice probably vary depending on the volcano that produced it. Here is a typical analysis of a pumice. https://www.srilava.com/pumice-stone/?lang=en There is plenty of calcium but it is probably as the silicate, which will only leach out into the rhizosphere very slowly compared to the carbonates. The aluminium and titanium are not so good for the plants, hopefully they are also as silicates. Though I think alumina does not get soluble until you get down to about pH 4.

Note the sodium content, which is why you should soak and rinse your pumice very carefully with abundant water before use. Unless you are growing a halophyte.
gerald wrote:
Sat Mar 27, 2021 9:52 pm
Don't add Epsom salts or anything else for that matter because you will cause a salt imbalance which could be toxic. In this case too much Epsom salts (magnesium) means the plant will have a hard time taking up calcium.
As Chempak just have "Also contains Magnesium." on the packet it is, unfortunately, impossible to know how to adjust for different plants that may have requirements for extra magnesium.

gerald wrote:
Sat Mar 27, 2021 9:52 pm
You're better off giving a low dose of feed (say 50% strength) with every watering.
I definitely agree with that, five meals a day rather than one huge supper.

gerald wrote:
Sat Mar 27, 2021 9:52 pm
Use a proper pH meter if you can, the cheap test kits are useless. Vinegar will do it but so will citric acid which is easy to find and very cheap.
Bromothymol blue liquid (usually sold as pH 6.0 to 7.6) is good enough for me and does not need £60, regular cleaning, calibrating nor batteries. Clear results but should be read in natural light. The Chempak should adjust most waters to the correct pH.
A few things :geek:

If you're in a hard water area there is no need to add calcium to your feed. If you are in a soft water area (Manchester?) then you might need to choose a feed that has calcium, there are feeds on the market that distinguish between soft and hard water areas.

Magnesium is primarily used by plants as a component of chlorophyll. Therefore plants with a lot of green leaves will probably need quite a bit more Mg than cacti, which I can't see having a great requirement for Mg at all.

Chempak doesn't alter the pH of water. You must use an acid. I haven't used Bromothymol blue liquid as a pH indicator so I can't comment on that but use whatever works for you.

And pH meters don't have to cost £60 either, you can get them for way less
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Re: pure pumice?

Post by Pattock » Mon Mar 29, 2021 8:23 pm

gerald wrote:
Sun Mar 28, 2021 8:19 pm
A few things :geek:

If you're in a hard water area there is no need to add calcium to your feed. If you are in a soft water area (Manchester?) then you might need to choose a feed that has calcium, there are feeds on the market that distinguish between soft and hard water areas.

Magnesium is primarily used by plants as a component of chlorophyll. Therefore plants with a lot of green leaves will probably need quite a bit more Mg than cacti, which I can't see having a great requirement for Mg at all.

Chempak doesn't alter the pH of water. You must use an acid. I haven't used Bromothymol blue liquid as a pH indicator so I can't comment on that but use whatever works for you.

And pH meters don't have to cost £60 either, you can get them for way less
Magnesium is used by plants in much more than chlorophyll. There are magnesium sinks in growing roots and shoots as well as developing seeds. Without leaves I am not sure how easy it would be to spot magnesium deficiency at an early stage.

Magnesium has been found at 918mg/100g of dry matter in spinach, 884mg/100g of dry matter in nopales. I would not say that was a very big difference. Calcium was at 1.15g/100g of dry matter in spinach, 2.79g/100g of dry matter in nopales. https://fdc.nal.usda.gov/fdc-app.html#/ ... /nutrients

Your water is very hard at just shy of 243 mg/l CaCO3 equivalent and would provide about as much calcium for the plants as my fertiliser at 0.5ml per litre. It will also act as a strong buffer to changing pH. Though I must admit I was saying Chempak should change the pH, not that it does. I have no experience with it. My fertiliser does change the pH, to round about 6.2 to 6.4 every time. https://www.thameswater.co.uk/help/wate ... ts/OX495EJ (Randomly chosen postcode.)

My Manchester water (or should I say Lake District water?) has about 25mg/l CaCO3 equivalent so would definitely need supplementing from somewhere. It would be interesting to know if the calcium silicate in pumice was sufficiently available. Silicon is a plant nutrient that is very hard to deliver and helps many plants defend themselves against fungi. The combination might be why many growers swear by pumice. I wonder where those growers group in the water hardness areas. https://www.unitedutilities.com/help-an ... r-quality/

My experience with pH meters is that anything cheaper than £60 and 90% of customers are satisfied and don't return them to swap for one that works within a few weeks of purchase. The faulty one gets sent back to the manufacturers to recondition and then is sent out again.
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