Pine Bark Fines and Soil ph or Acidity
A message was posted last week asking about a Turface MVP soil mix formula. It caused me to reflect back on why my use of this inorganic potting medium method failed. Many many of my young rooted cuttings, after re-potting into the grit, calcined clay, and pine bark mix suffered from root rot and failed. I originally attributed a summer heat wave, compounded by over watering to be the root (no pun) of my problem. Now I will add another possibility, as I never thought about the potting medium itself and the role of soil acidity, or pH, until today.
This week, a fellow fig forum enthusiast steered me to this post titled "Osomocote" (that is the spelling in the thread) at http://forums.gardenweb.com/forums/load/fig/msg071148154271.htmlshared. There is a potting medium recipe offered by Mountainman0826. The one constituent recipe element that caught my attention was Powdered Dolomitic Lime. All this morning, I was wondering why the use of dolomitic lime, until I remembered some questions posed to me by Henry (hlyell) who was coaching me to help understand possible causes for my root rot. As for Powdered Dolomitic Lime, it is an old friend. I use it all the time, but not in my gardening and not in my fig propagation. Well, it seems I missed some passing recommendations to add this material when I created my mix of grit, calcined clay, and pine bark. And if it was an important ingredient, then it was another factor in the root rot situation.
If I was a betting man, I would bet that I used to much pine bark, with young fig roots, and no limestone to offset the low pH caused by the pine bark fines.
So, here is what I do know. Also, I apologize for what I do not know, but I did some simple tests of pH against the ingredients I have been using around the figs and my pond:
So, this afternoon, while thinking about the Mountainman (MM) recipe, I wondered why MM suggested using a cup of dolomite limestone. I can offer 1 really good reason, although there might be more. Pine bark fines are acidic and the dolomite will counter the impact of that soil amendment. I did an experiment, just today. I had a plastic container with some old pond water that I was using to wash my pine bark chips. The container still included 2 or 3 cups of waterlogged pine bark. Well, I just tested the pH of that water solution. Today, my pond water is at 8.33 pH and the standing water in a plastic pail of pine bark chips is 3.45 pH. I was not surprised, just deflated. I should have known that the pine bark would work to lower the soil pH. I dumped a planted nursery pot the other day and (on my honor) ran and showed my wife how it seemed there were pine bark fines clumped around the dead and rotted roots. I blamed my self for the uneven incorporation of the soil mix and for the local areas of clumped fines and concluded that wetness around the roots was the cause. Today, I say that the acid in the fines might also have played a role in the plant root loss.
Separately, I took a portion of Miracle Grow Potting Mix and filled a container to half-full and then filled it with 8.30 pH pond water. After stirring and allowing for settling, the pH of the water was tested at 6.98. The Miracle Grow mixture tested out to be a somewhat acidic , as it lowered the pond water pH, but it did not do so to the extent of the pine bark fines alone (6.98 vs 3.45).
Dolomite limestone: Here is how it works in my pond:
My back yard is shaded with a stand of 40 foot tall pine trees. The prevailing winds shed loads of tree material into the pond all year around. You might think a pine cone will float forever. The same with pine needles. Well, they sink. These items are buoyant for about 24 hours and then they sink. Between fish naturally discharging ammonia based waste products, the pine trees, and the township well water, in general, sometimes I like to put some alkaline buffer into the pond. Too, pond plants generate carbon dioxide and this turns to carbonic acid. So, I add a dolomite limestone slurry right into the pond. My pond fish thrive in the environment. Use enough and it will bring the pond water up to ~8.0. Below ~8.0, the limestone actively dissolves and causes pH to return to ~8.0. At ~8.0 pH, equilibrium is reached and excess limestone simply rests at the pond bottom, like sand, until pH starts to fall, when more limestone will dissolve to bring pH back to 8.0. Above ~8.0, the limestone is passive in terms of pH. In terms of nutrient value, I do not know if high amounts of limestone are counterproductive. I would guess not. Bottom line, while the use of dolomite might have some mineral nutrient value, to fig plants, if there are acidic pine bark fines, that acid will be neutralized in the presence of limestone.
Next time I use pine bark fines, I will be sure to include an appropriate portion of Powdered Dolomitic Lime.