Soil mix test results 2

[GavinG]

SOIL TESTS: SECOND LOT.

The first four tests used potting mix sifted through fly wire to remove the dust. It was mixed 50/50 with Mt Sylvia diatomite, brick dust, perlite and spongalite (Richgro aquatic planting mix). This was to see whether the potting mix dust was the component that made the previous tests drain so slowly.

The next four tests used soaked and squeezed coco peat as 25% of the mix, being a more realistic mix than the previous dry 25% coco peat, which expanded remarkably when wetted. The other components, making 75%, were diatomite + perlite, diatomite on its own, brick dust and spongalite.

Two other tests contained 20% soaked and squeezed coco peat, to compare with the 25% mixes, again with diatomite + perlite and diatomite on its own.

Once again, a rough measure of drainage times was recorded. The water retained was measured differently, as damp and wet components were used in the mixes - the weight after drying for four weeks was subtracted from the weight after a one minute soak and a ten minute drain. The mixes may possibly dry even further in the next two weeks, but I got bored.

I can send the results/number salad/junk pile as a PDF to anyone who wants, but here are the conclusions.

The sifted potting mix drained more rapidly than the unsifted mix, but never as fast as the coco peat mixes.

Perlite as a component appeared to speed drainage, but reduce water retention, compared to diatomite.

None of the other grits appeared to make a great difference with drainage times - its the type and size of the absorbent component that determines the drainage speed.

Once again, coco peat (at 25%) retained as much water, sometimes more, than 50% sifted potting mix, but gave much better drainage.

Spongalite appeared to retain more water in both types of mix than diatomite, brick dust or perlite.

Diatomite appeared to hold water better over time, as a component in the mixes, with spongalite second best. Brick dust and perlite had lost more than 40% of water within a day.

If you are using the slowly absorbent grits like spongalite and diatomite, it may be worth soaking each tree once a week through summer.

A 5% addition of coco peat (from 20% - 25%) increased water retention by more than 10%. Drainage, while still good, was very slightly slower.

Adding perlite to diatomite mixes seems to reduce water retention, without any other great benefit.

So now to the Great Acid Test - my first Canberra summer. I have previously used sifted soil, composts and coarse sand, so its all going to be Verry Interresting!

TEST YOUR MIXES! And thanks for your attention.

Gavin

[kcpoole]

cool Gav Nice report

Ken

[GavinG]

After these tests, I used four different blends this year: 50/50 diatomite and sifted potting mix, 80% diatomite 20% coco peat, 80% brick dust 20% coco peat, and 80% spongalite (Rich Gro Aquatic Mix) 20% coco peat.

Everything grew reasonably well, but clearly needed more fertilizer than I usually doled out, with the potting mix blend a bit less hungry. I found it interesting that brick dust seemed to reduce internodal distances on maples very nicely, without starving or drying out too quickly.

The nasty surprise came with repotting this month - everything in the spongalite blend had suffered badly, with the spongalite forming a thick clay pan on the base of the pot over winter. Two of three maples and an elm in this blend are now marginal, and may die.

P1050153.jpg

This is all that was left of the root ball of a large maple.

P1050155.jpg

And this is the bog that formed over winter, causing the rot. No outward signs of trouble.

I believe that the Rich Gro Aquatic is now diatomite, but I'd strongly recommend never using spongalite for bonsai, if it comes back on the market.

Gavin

[Dario]

Hi Gavin, and good on you for sharing the results of your tests mate! I am currently using pine bark sifted from potting mix (40%) and diatomite(60%), some have an additional 10% of chopped spagnum moss added. These are for poly box growing on stage as I don't own "finished" bonsai at this stage...most of my material is collected...a good 10 yrs off...some nice stock/urban yamadori though! Anyway, I find this sort of info most useful!
I have followed a few of the different soil mix tests on this site and appreciate them all!
I am sorry to hear about the trees in the spongalite /coco mix...hope they pull through for you!
It would be great if you could take the time to send the results via pdf to me!
Thanks again, Dario.

[Steven]

Sorry I missed this when you first posted it Gavin. Thanks for an informative repo[r]t!
This along with Grants Diatomite and similar properties testing and Potting Mix Tests Results Abbreviated are a must read for anyone serious about bonsai.

Regards,
Steven