pH 5.2 vs 6.2?

Douglas.Curtis said:

'Proper' pH depends on the type of system your plants are in.

Roots-out systems, where the roots dry out between waterings, have a natural pH drop during the dry out period. 'Proper' pH range will vary with each system but top and bottom pH (edit: of your nutrient solution) will generally be 5.5 to 6.1.

Roots-In systems, where the roots are constantly exposed to the nutrient system, do not have a 'dry out' induced pH swing. Best results are obtained by setting the pH at 5.4 and letting the pH naturally rise as the plants eat nutrients. Res size determines how fast this swing occurs. 5.4 - 5.8 is where you're going to find the best results with these systems.

Just figured I'd clarify.

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Douglas.Curtis said:

'Proper' pH depends on the type of system your plants are in.

Roots-out systems, where the roots dry out between waterings, have a natural pH drop during the dry out period. 'Proper' pH range will vary with each system but top and bottom pH (edit: of your nutrient solution) will generally be 5.5 to 6.1.

Roots-In systems, where the roots are constantly exposed to the nutrient system, do not have a 'dry out' induced pH swing. Best results are obtained by setting the pH at 5.4 and letting the pH naturally rise as the plants eat nutrients. Res size determines how fast this swing occurs. 5.4 - 5.8 is where you're going to find the best results with these systems.

Just figured I'd clarify.

Click to expand...

mushroombrew said:

I would say it is also strain dependent. Mag hungry OG's don't like 5.6(Mag valley)

I have run 5.2-5.5 and 5.8-6.0 with OG's and they perform the same.

If you do run 5.2 I suggest letting it drift up to 6.0 periodically.

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Daniel_Norway said:

Thanks. I now measured pH of 70% coir + 30% seramis, leached with 2 times pot volume of tap water (0,2mS/cm) and 1 volume RO. It is 6.3.

In my initial post I wondered if any charts exist for coir, thinking it might well be a bit different in coir compared to the posted chart which is for a specific mix. But there is one more variable I read about here: How much available nutrient vs pH depends a lot on what molecule the ion is part of, if part of sulfate it is soluble at much higher pH than if oxide, it says.

Coir has the highest CEC of all potting mix materials per volume, and what counts for potted plants is per volume not per weight. And as Bunt said, CEC mainly affects divalent ions, most monovalent ions remain water soluble.

Testing pH of fertilized soil might be a good idea. Due to Coir and my usual fert both being a bit high on K and seramis adding to the K I decided to add some Ca+Mg (an N), found a suitable bottle called "Magne-Cal". I should buy that first before testing.

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• "Manganese toxicity is common in acid soils below pH 5.5. On the other hand, manganese deficiency is most common in soils with a pH above 6.5. One of the main reasons for liming acid soils, especially for legumes, is to prevent manganese toxicity. The amount of manganese in solution decreases 100-fold for each unit rise in soil pH (as from 5.0 to 6.0). Where manganese deficiency exists as a result of high pH, it is easier to correct the deficiency by adding a manganese fertilizer than by attempting to acidify the soil."
• They seem to say the left chart applies to mineral (loam) soils and the right chart to soils with >6% organic matter but that exact shape depends on amount of organic matter - so it doesn't sound like the right chart is for soilless media or hydroponics but for soils high in organic matter: "Soils high in organic matter (more than 6.0%) and near neutral in pH (above pH 6.5) may be deficient in manganese. As the organic matter content increases, the amount of exchangeable manganese decreases due to the increased formation of organic matter and manganese complexes." And in fact Bunt says that what Lucas & Davis pointed out in 1961 was that organic soils have optimal pH range 5,0-5,5, i e 1,0-1,5 units lower than mineral soil. So the righ chart applies in principle to all organic soil mixes, with some variations.
• "Foliar applications of manganese reduce chemical fixation [in organic soils] by reducing contact with soil particles."
• "Manganese treatment is recommended if the soil tests less than 10 ppm. When soil organic matter exceeds 6.0%, the availability of manganese is based on soil pH. Manganese is recommended if the pH is above 7.0."