I found Pumice!!! Part 2 ;)

02 Oct

Okay, I’m not going to say where I found it, until I have it in my hands, but I’ve ordered some horticultural grade Pumice and the supplier assured me there would be no hiccups.  Fingers crossed!  And of course, if it arrives as promised, I will share where I found it 🙂

On a side note, I’ve been tirelessly researching alternative substrates (the pumice situation was looking hopeless) and have discovered some interesting substitutes that many people seem to swear by!

The Ottawa Bonsai Society uses the following mix (I would omit the CPM for Lithops but otherwise, it’s a nice gritty mix that is easily sourced locally).  I’ve personally used this mix and it works well.

  • CPM (composted pine mulch) – available at Artistic Landscape on Bank Street in Ottawa
  • Turface MVP – available at Richie Seed & Feeds in Ottawa
  • Chicken grit – available at Richie Seed & Feeds in Ottawa

Another Bonsai grower I contacted uses ‘Qualisorb’ and buys it from Canadian Tire.  I bought a 20 lbs bag for $13 dollars.  It’s a 99.999% calcined diatomaceous earth product that is rumored to be very good in gritty mixes if you can’t find Pumice.  It has less than 1% silica in it, but if that bothers you, it is easily sieved out.  Just be careful not to breathe in the dust of this product.

And finally, can you believe ‘Tidy Cat’ offers a fired clay litter for a fraction of the price of fired clay soil mixes and growers are using it with great success?!  I was impressed!  You can find it at your local pet supermarket.  I would have bought a bag but the one my local store carried was 40 lbs and I wasn’t keen on lifting it into my shopping basket; and besides, I had just purchased the Qualisorb from Cdn Tire so I didn’t *need* it, but it’s a great option for those who are struggling to find suitable substrates at a decent price.

So what exactly is gritty mix?  Well, it’s a mix of gravely substrates that works well for Lithops, Cacti, and Bonsai.  It is fast draining enough to prevent your Lithops from rotting away, but holds enough moisture to keep the Lithops fat and happy for a reasonable period of time.  The simplest gritty mix I’ve seen was 100% Pumice (or substitute).  More frequently, I’ve seen Pumice (or substitute) mixed with cactus soil mix at a ratio of 1:1.  I’m up in the air about that one but so many people have great success with it – I would feel confident using it.  Then I’ve seen the three part mix mentioned above.  If I were building the three part mix, I’d replace the CPM with the cactus soil mix.  Ooooooo…and I’ve also seen a whole bunch of different gravely bits from various sources tossed together and it seems to work too.  I think the moral of the story is that as long as the mix is well draining but some of the pieces still manage to hold onto some moisture, you are doing okay.

I’m going to do a little more research and will hopefully have worked out a gritty mix that I’m comfortable with before my new L. Fulviceps arrive 😀

Stay tuned!


Posted by on October 2, 2014 in Wouldn't You Like to Know


2 responses to “I found Pumice!!! Part 2 ;)

  1. Bob Stewart

    October 2, 2014 at 4:37 am

    You give a good discussion of substrates for plants with good drainage and aeration requirements. I agree there are many possible mixes as long as they end up with good drainage and some water and nutrient retention. I will offer one note of caution about one commonly used substrate in commercially sold cacti and succulent potting mixes; sphagnum peat has a special problem, it’s hydrophobic. When sphagnum peat is allowed to get dry, which often occurs in potting media for succulents, it resist getting wet again. While many commercial growers of cacti and succulents used sphagnum peat in their potting media, they also always use a wetting agent and are careful to not allow their media to get completely dry. Potting media for succulents don’t have to completely dry out as long as the structure is such to allow constant air movement into the root zone. Over-watering doesn’t kill plants, it is lack of air, and thus oxygen, to the roots. If the structure of the potting media isn’t coarse enough, water will fill all the available open spaces in the media, there will be no air, and the roots will die from lack of oxygen.

    A few succulents, such as Lithops, have an additional problem in that they will absorb water as long as it is available, and thus the water content of the potting media has to be controlled. This is were the use of sphagnum peat as a component of a potting media is a problem. You said it well, there are many mixes that will work if they meet a few basic requirements. I notice you haven’t mentioned perlite. It is probably the most widely used drainage improving potting component by commercial nurseries and greenhouse. It is also widely available to the average grower. While I don’t like the way it comes up to the surface of the potting media, it does improve drainage, is available and relatively inexpensive, and can be used to grow good succulents.

    After adequate light, using the proper potting media is the most important requirement in successfully growing succulents. I’ve enjoyed your discussion thus far and look forward to learning which mix you finally decided to use. 🙂

  2. bonseyes

    October 2, 2014 at 11:28 am

    Hi Bob. I’m glad you enjoyed the discussion. I had read that sphagnum peat was bad, but no one really went into detail as to why. Finally, with your explanation, it makes sense! Thank-you!

    Over the last couple days, I’ve been reading a lot about substrates becoming hydrophobic. I’d never heard the term before but it seems to happen often enough – in both the Lithops and Bonsai worlds. And Lithops of course, do go through completely dry periods, so the problem is compounded in our Genus. It’s really the wetting agent in the cactus soil mix that worries me. I had no idea they were adding something like that; it seems completely inappropriate an illogical!

    I am interested in soilless mixes for Lithops, but with our climate and the success of others from similar climates, I’m cautious to go completely soilless. I’m going to research this some more over the next few days and hopefully come up with an appropriate mix. I did want to keep the organics below 10% so maybe I’ll just use the volcanic soil I have on hand – while it is mineral and nutrient dense, I don’t think it would hurt in small quantities.

    As for Perlite…I don’t like how Perlite floats to the top of the pots. It looks awful after a short period of time and will fly right out of the pot during misting if you aren’t careful. I have to wonder, if it floats to the top of the pot, is it really doing its job in the middle and bottom layers? These are just casual observations and yes, Perlite is used, with success, by many growers so I really should have mentioned it. I still have a part bag of Perlite too so I wouldn’t be surprised if it made a cameo appearance in my new mix – haha! – but I don’t think I’ll be relying on it as heavily as I have in the past.

    Thanks again for taking the time to provide such a well thought out comment, Bob. I will be posting about the new Lithops substrate once the Pumice arrives 🙂

    P.S. Have you heard about people using Zeolite? I just read about it yesterday and it seems to be coming into favor for horticultural use. In Canada, we can buy it in large quantities from Aquarium supply stores (its used as a filter material) so this is potentially another option.


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