Soil blend for coastal live oak

Hi folks,

Looking for recommendations on a soil mix for coastal live oak (Quercus agrifolia) that does not include akadama. The tree is only a couple years old and is still developing in ~3 gallon pot.

My standard mix is equal parts lava/pumice/DE. So:

  • Put it in DE boon mix? or
  • Put it in pure DE? or
  • A different mix?


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If you’re growing out a trunk or want fast development, i’d go pure sifted pumice. You’ll need to water more frequently compared to if you were using a mix containing akadama, Pure sifted pumice works great for rapid growth. I use pure pumice for newly collected trees or trees where i’m trying to thickening the trunk or branches, something that’s not yet in refinement. You could also just add a small amount of akadama to your pumice if you want a good grow mix-like 10-20%.

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Query: why do you say pumice is superior for thickening? My understanding is that thickening is a purely a function of resource passage through a given area, which is best facilitated by a balanced soil mix (e.g. Boon).

The faster your tree grows, the faster you’ll get thickening. The more vascular tissue, leaf mass you build up the thicker your trunk or branch will get in order to support all that mass. If you have good soil, ground growing is likely the fastest for thickening. Pumice is good for rapid growth and producing a strong root system inside a container, it’s also very inexpensive at least in CA. Once you have a trunk and start working towards refinement, i’d switch over to pumice, scoria, akadama. I’m not sure about DE, i’ve never experimented with it. As Ryan mentioned in a previous stream, Kanuma has also been used for Cork Oak in Europe with success. Coast Live Oak seem to do great in Akadama mixes, but we could experiment with subbing out and trying different ratios of Kanuma instead of Akadama if your looking for something else as mentioned in the original post. Random note-I think Kanuma mixes may also be key in growing Manzanita-another CA native.

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Thank you so much for the comprehensive response! That matches my understanding. What I’m curious about, though, is why pumice is good for rapid growth and root growth – why it would be better than pure akadama (or kanuma – crazy about it and cork oak!) or Boon mix. Any ideas?

I might not be the best to give you a good scientific/analytical break down of exactly why Pumice. What I can tell you is, that it allows for a lot of oxygen in the roots and has good water/nutrient holding capacity. Pure sifted pumice allows more oxygen compared to Akadama. Pumice is does not breakdown and scale like Akadama does. Akadama is good for healthy but controlled growth. Before I tried pumice, I used Turface and bark. After switching to pure pumice I quickly learned what a healthy and robust root system actually looks like.

Here’s an interesting read that goes into more depth about soils: 55

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