Silly Gritty Mix question - ratios?

4 years ago

This is an absurd question I know but I just wanted to clarify that the 1:1:1 ratio of the gritty mix is according to volume quantity and not weight i.e. 1 cup of bark, 1 cup of grit and 1 cup of turface as opposed to 1kg (for example) of each ingredient.

Also I had planned on creating a large batch of the mix to use for various pottings - is this advisable or should I proportion a mixture for each separate planting?

Thanks in advance!

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tapla (mid-Michigan, USDA z5b-6a)

4 years ago

The proportions are by volume.

I had planned on creating a large batch of the mix to use for various pottings - is this advisable or should I proportion a mixture for each separate planting? How I approach things: As long as I have everything assembled and the Turface screened. I make several small batches such that the total volume made in any day-long session would be somewhere between 50-100 gallons, and I store them in 32 gallon heavy duty trash containers with wheels and keep an 18 gallon tub with rope handles ready at hand.

The gritty mix is very easy to alter so it has more or less water retention. I make the 1:1:1 ratio in large quantities, then alter enough mix to suit an individual plant. While I almost always suggest any alteration should include more Turface MVP and less grit (for added water retention), or more grit and less Turface MVP for less water retention. Adjustments can as easily be made by simply adding a handful or two of one or the other to change water retention. Ideally, the bark fraction should remain at 1/3 of the mix, or less, to ensure the medium's structural integrity over the long term.

The beauty in being able to use large particles of Turface MVP or grit to adjust water retention lies in the fact that aeration remains consistent and there is no need to suffer the consequences of relying on perched water to increase water retention. Water is still held on the surface of soil particles, in the internal pores of materials with open internal porosity, and at the interface where soil particles contact each other, leaving spaces between soil particles full of air from top of the soil column to the bottom of the pot. This results in a very healthy environment for roots, 'healthy roots' being an essential prerequisite to a healthy plant.

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Comments (10)

HU-369225117
Original Author
4 years ago
Thanks so much for replying to this Al! I feel honoured.

While I have your attention, I was concerned that I had misunderstood your teachings on this mix when I watched the following video:

https://youtu.be/jb4e62BhNnY

because my screened particle size for the turface component (or equivalent) starts at 2mm whereas the narrator of that clip constantly stresses the need for all the particles to be of the same size. I based my sizes on some of your previous posts but have I made a critical error?
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tapla (mid-Michigan, USDA z5b-6a)
4 years ago
While it's true that aeration and drainage can be improved by ensuring all soil particles are precisely the same, it's not a perfect world and I'm quite sure growers are not going to be willing to discard 1/2-3/4 of the material purchased to make the Gritty Mix on the altar of uniformity. I can see that Ashley doesn't have a command of the concept that underpins media like the gritty mix, and she doesn't understand the physical characteristics of the ingredients she discussed. To wit, as uniform particle size increases, the ability of a mix of ingredients to hold perched water decreases, until, at a uniform particle size of approx 1/10", the mixture is incapable of holding perched water. This is a function of the sum of the forces of adhesion (water's tendency to stick to other objects) + cohesion (water's tendency to stick to itself) is not enough to resist the gravitational flow potential of water in the grow medium. Variance in the sum of adhesion + cohesion is almost entirely due to an increase in adhesion that occurs as the % of ingredients <1/10" increases, very simply because the surface area (and therefore the force of adhesion) of a pint of BBs is much greater than the surface area of a pint of marbles.

So while she is technically correct in thinking that in a perfect world it would be best if ALL particles in a medium were the same size, it's not practical. One solid reason has to do with the decrease in the size of bark particles. If you started with a 'perfect mix' in which all particles are 1/10 of an inch, it should hold no perched water; however, what happens as the bark particles undergo composting. The bark particles are purposely larger (1/8 - 1/4") in the gritty mix to allow for a decrease in size as the bark breaks down.

I stopped listening to what she had to say about 8 minutes into her video because I recognized she is operating at beyond the limits of her knowledge. I don't regard what she said as being seriously misleading, but people need reliable information to make good decisions.

Al
chamaegardener (Z5) Northeast Illinois
4 years ago
fyi: 25mm per inch

1/4" about 6mm

1/8" about 3mm

1/10" is 2.5mm

1/12" about 2mm

I prefer working in milimeter
ken_adrian Adrian MI cold Z5
4 years ago
i had a spare plastic garbage can ... and i keep it filled with DRY media .... leave the top off until it dries ..

this can has had media in it for about 20 years... already to go ...

ergo .... presuming you will need more in teh future ... make more and store it ...

if wet ..... it can break down ... get funky.. ergo ... dry is better ..

besides ... if you only make enough for one pot.. you are still going to have to store all the components anyway ... so may as well mix them up.. and store them together ...

ken
gardengal48 (PNW Z8/9)
4 years ago
"I prefer working in milimeter"

Few of us in the US do :-) The conversion to the metric system has never really caught on here.
chamaegardener (Z5) Northeast Illinois
4 years ago
Gardengal, I am a retired goldsmith in the US.

Diamonds and gemstones are always measured in millimeters, not fractions of an inch. :^)
gardengal48 (PNW Z8/9)
4 years ago
Potting soil ingredients hardly qualify as gemstones :-) And regardless of your background, the vast majority of US citizens have little to no concept of metric equivalents nor do they have much reason to use them.
chamaegardener (Z5) Northeast Illinois
4 years ago
They hardly qualify as lugnuts either. We are discussing small distinctions that millimeters are more useful in distinguishing. Sorry my contribution does not meet your needs, I will be quiet now.
jane__ny
4 years ago
Are you using this mix for orchids?