Pumice and Lava rock size?

[EclipseFour20]

Frank--

Using OilDri, I experienced something similar to the deficiency issue when it was around 10-12% by volume. At 6% or so, it brought me all the benefits of clay without any compaction/air porosity issues.

But then again, I also use an atrocious amount (6.8%) of Fossil Shell Flour (food-grade DE) and equal amounts of bark, Promix BX, perlite & vermuculite (around 18% each) as the backbone of my grow medium.

Almost every summer I experiment/goof around with different grow medium aggregates and techniques (summer veggies are great "guinea pigs"). And when I find something worthy to add to my "indoor grow medium"--I invest the time and conduct a series of air/water porosity tests to recalculate the exact amount of each aggregate will be needed. That way--one can address compaction and excess porosity issues.

I wish it was as easy as "I'll add a bit of this and a dash of that" to the new recipe and everything will be perfect. Air/water porosity is one thing--anion and cation exchange rates are another--and C:N ratio is a completely different topic. Change one--and you probably effect the other. Besides, grow mediums with greater CEC capacities require less quantities of fertilizer/nutrients...so now you gotta reduce the amount of water soluble ferts/nutes required! Hard to make one change without adjusting something else!

Developing the "perfect grow-medium" is quite an investment/art; but well worth it!

Cheers!

 

[canna woop!]

I have thought that perlite, pumice, whatever do wuite well in the worm bin. Never sterilized it and dont believe i will. I have thought of designing soil cooking ovens before but it was more like one of the things you can agree with people about at the hydro store- IOW, a joke

 

[dank.frank]

Eclipse - I've run countless mixes. I was probably one of the largest proponents of the calcined DE until I couldn't get certain "burn" like markings to vanish.

I try to keep things, some what simple on the base medium itself. If I can get away with using 1 aeration amendment vs 3 or 4 or different sizes, etc - it is ultimately simpler.

I use food grade DE in my soil mix as well - have been for about 4-5 years now...at least. However, I use it MUCH more sparingly than you do. I think of it as another amendment as opposed to thinking about it as part of the base mix.

I can't imagine having nearly 7% of the entire medium food grade DE - I know I'd have all kinds of issues if I did that!!!



dank.Frank

 

[EclipseFour20]

Eclipse - I've run countless mixes. I was probably one of the largest proponents of the calcined DE until I couldn't get certain "burn" like markings to vanish.

I try to keep things, some what simple on the base medium itself. If I can get away with using 1 aeration amendment vs 3 or 4 or different sizes, etc - it is ultimately simpler.

I use food grade DE in my soil mix as well - have been for about 4-5 years now...at least. However, I use it MUCH more sparingly than you do. I think of it as another amendment as opposed to thinking about it as part of the base mix.

I can't imagine having nearly 7% of the entire medium food grade DE - I know I'd have all kinds of issues if I did that!!!



dank.Frank

Frank...sorry, missed reading your post earlier.

The burn thing is probably due to "excess ferts"--as mediums with high CEC rates are more "efficient" require 20-40% less fert$.

I view Fossil Shell Flour as a "nutrient" (plant available Si)...as well as an "amendment" (increase in water absorbancy and air porosity); the benefits of greater CEC ratio is a pure bonus...with almost zero impact on the soil's PH.

So...you think 7% by volume of DE is too much? Axis suggest using 10-20% of their DE product in potting soils, Agripower studies suggest 6-12% was most effective. Using 6.8% is what works for me--and is in harmony with the rest of my ingredients.

Perhaps another way of thinking about Si...is to compare the rate in nature (earth's crust is 25% silicon) against what we use in our garden (packaged grow mediums contain almost 0% silicon). So...adding goodly amounts of DE (85% silicon) is one "organic" answer that allows me to to "mimic nature".

Hope this helps...cheers!

 

[dank.frank]

Yeah, I'm with ya Eclipse...just DE isn't my only source for silicone.



dank.Frank

 

[rickyjack9]

imho rinsed pumice is excellent enf any grade. I like small.