Pumice as substrate..

[fredman]

Pumice is in abundance here in NZ and very cheap. I buy it from a wholesaler at $7 per 20kg bag. Nothing else is being allowed into the country, so I'm restricted to using only that. I even mix the sifted fines into my grow beds.... I came to realise that it might actually be a good thing (saves me the confusion of trying all the others. I can concentrate on it alone, and get to know it as best I can).
I'm now contemplating using ONLY it as substrate. Is there anybody out there that uses it exclusively on different species? Would like to hear experienced opinions on using it as a only substrate...?

I planted one of my less loved Azaleas in straight pumice two seasons ago, to see how it will do. Turned out great. Out grew the others by a fair way. It did get chlorosis this spring however. The ones in organic based mix did not get the chlorosis. Not sure if its feeding related...? Maybe the pumice needs feed more often....?. Maybe it doesn't hold onto its nutrients the way the organic mix does...? Maybe something else...?

This year I planted a few more Satsukis in pumice but I mixed in chopped sphagnum moss.

I did a simple test yesterday. Broken up pumice (1/4inch) completely saturates within a few seconds when dunked in water. It holds almost 50% moisture. I left it overnight in a bonsai pot on my bench, the next day it still had that 50% moisture. Will weigh it again a few times during the day. I want to see how long it holds on to the moisture on its own. Not very scientific and not taking all the variables into account really..... just a rough indication...

 

[Eric Schrader]

I have an oak planted in pure pumice. It's never been happier. You might try adding the sphagnum to the top rather than mixing it so it doesn't rot in there. And try fertilizing with organics to offset the mono-structure within the soil. But by all accounts pumice as a pure medium is among the best. The drawback is that you can expect growth to be longer and stronger than in a medium that retains moisture and nutrient more.

 

[Eric Group]

It is a suitable substrate. Azaleas could probably benefit from some bark mixed in or something like that... You do need to fertilize more with a substrate like that... Use some organics and you oughta get more nutrients and fewer leaf issues.

 

[fredman]

Thanks Eric. Didn't think the sphagnum can rot in there. That's a bit of a concern. I did use very little though. You found it to rot? Lots of oxygen going through there...
I do use sphagnum on all my satsukis as a layer on top yes. I also finish it off with a layer of pebbles on top of the sphagnum to keep it from drying out. The sphagnum tends to become hydrophobic when dry....

 

[crust]

I have added spag(10%) to pumice/Perlite mixes with good success.

 

[Andrew Robson]

I have an oak planted in pure pumice. It's never been happier. You might try adding the sphagnum to the top rather than mixing it so it doesn't rot in there. And try fertilizing with organics to offset the mono-structure within the soil. But by all accounts pumice as a pure medium is among the best. The drawback is that you can expect growth to be longer and stronger than in a medium that retains moisture and nutrient more.

I agree with Eric! When using a substrate like pumice, lava, or even akadama, putting some sphagnum or yamagoke moss on top of the soil can be pretty beneficial in retaining moisture. It also produces better feeder roots!!!

Cheers!

 

[michaelj]

I have a lot of trees in pure pumice, all doing well.

 

[sorce]

rot in there

If you would Eric....
I have cursed sphagnum for 2 years now cuz I have an idea it "rotted" for me over winter...it didn't breath well....and in turn rotted my roots.....

You reckon I can stop Thinking my depot Mosser lee sphag is poisoned!?

Thank You!

Sorce

 

[Andrew Robson]

Some advantages to pumice over lava: http://crataegus.com/2009/02/23/lava-woes/

 

[wireme]

Regarding your moisture retention test, I'd be really interested if you try a couple more things.
Rather than soaking pour it through as you do when you water, try it twice, pouring just till it runs out once and longer for another batch.
Some of my trees in pumice dry out quicker than I would like, sometimes I wonder if the pumice is staying dry inside the particles after watering.
As far as sphagnum rotting, sure it will, of course, as will any organic component, what's the problem?

 

[Shima]

This year I planted a few more Satsukis in pumice but I mixed in chopped sphagnum moss.

This is my mix for everything except satsuki where I use only pumice as in Japan where they use only straight kanuma which is their version of pumice. never a problem.

 

[fredman]

The reason I added some sphagnum is to get the pH down as azalea likes it. Whether it will have the desired affect I don't know as yet. Kanuma as I understand has a lower pH that suits azalea very well.
How do you find pumice alone Shima? Have you been using it long?

 

[fredman]

WoW I only now saw all the positive comments above.. don't know how I missed that. Thanks for the feedback

Wireme. I actually tied 100g pumice in a net...

...and dunked it for 5 sec, then weighed it. I then held it under water for 5 minutes and weighed it again. The weights were the same....
I got 100g pine bark soaking overnight now (the bark is the same size as the pumice). Tomorrow i'll saturate the pumice to. Im going to leave both hanging side by side in a draft less place, and weigh them every hour. I want to roughly see at what rate they loose their moistures....

As far as sphagnum rotting, sure it will, of course, as will any organic component, what's the problem

Is that meant like in a good rot, or bad rot? My logic still finds it difficult to understand how it can rot, with all that oxygen in and around the pumice...?

 

[fredman]

I have a lot of trees in pure pumice, all doing well.

What do you feed with Michael?

 

[Anthony]

Fredman,

100% pumice, would be most likely - Hydroponics
Which is fine as long as you look up hydroponics and the how to.

Hmm something else to test - ha ha - for next year.

Would probably end up sprinkling teaspoons of compost on the surface.
Keep up the learning.
Good Day
Anthony

* Already have a Ficus p. in 10 mm hand rolled porous earthenware clay balls, but added teaspoons of compost as time went by, you can lift the pot with the tree's trunk.
Done well.

 

[sorce]

Is that meant like in a good rot, or bad rot? My logic still finds it difficult to understand how it can rot, with all that oxygen in and around the pumice...?

Been bad for me.....

Mostly with it on top near the trunk.
But also mixed in at little amounts.

Love the water retention test!

Sorce

 

[Waltron]

Here is a great article with very detailed info and specific advantages to different soil components, definitely worth a read. my plan for this year's soil is to mix pumice, lava rock, pine bark fines, sifted DE oil dry, and sifted Clay oil dry.

http://adamaskwhy.com/2013/02/01/th...ised-long-winded-ever-lovin-bonsai-soil-epic/

http://adamaskwhy.com/2013/11/20/a-coupla-three-new-bonsai-soil-components/

random source for pumice. apparently its used for annealing.. very light so 4 lbs is a decent amount.

https://www.etsy.com/listing/175535...earch_query=annealing pumice&ref=sr_gallery_7

https://www.etsy.com/listing/207249...arch_query=annealing pumice&ref=sr_gallery_13

 

[Bunjeh]

I have settled on a mix of pumice and 20-30% decomposed pine bark (sifted) for everything. Works great.

 

[wireme]

Is that meant like in a good rot, or bad rot? My logic still finds it difficult to understand how it can rot, with all that oxygen in and around the pumice...?

Good rot, bad rot, dunno, rot is just another word for decomposition.
As far as creating problems, sphagnum or long fiber fresh peat moss is one of the most commonly recommended additives as far as organics go. I have one tree in a mix of pumice and sphagnum, doing great.
Your right about the oxygen, anaerobic conditions do lead to "bad rot" stinky and pathogen rich decay organisms.

 

[michaelj]

What do you feed with Michael?

The stuff in pure pumice gets the same rotation my other trees get, which includes Miracle-Gro, DynaGro, seaweed soup, worm castings and from time to time, random stuff that was on clearance.