Thanks Josh, I know the first time I made a mostly bark based mix a year or so ago, I saw pH fall to 4.5 and I freaked added more lime than was necessary and I wasn't seeing instant results and then over time seeing drastic swings in pH even in the same container. Hope to avoid that this time around.

Thanks Josh, I know the first time I made a mostly bark based mix a year or so ago, I saw pH fall to 4.5 and I freaked added more lime than was necessary and I wasn't seeing instant results and then over time seeing drastic swings in pH even in the same container. Hope to avoid that this time around.

Your pH will continue to rise. How fast depends on moisture content of the media, particle size of the lime, and temperature .... the wetter/finer/warmer things are, the faster the pH will rise; but a pH of 5.0 is fine in containers. 'Ideal' container media pH is about 1 full point lower than what is considered the 'ideal' pH for garden/mineral soils.

Al

Al would that apply to Hot Peppers and Tomatoes? I've always heard 6.0-6.5 pH. Why would containers need different pH requirements than in the ground.

Yup - it applies to peppers & mater, too.

I put the word 'ideal' in between the apostrophes (above) because it's something that's often said, and I'm guilty of repeating it as well, but lots of people with lots of letters after their name have said what I'm about to try to explain.

"Why would containers need different pH requirements than in the ground."

First, they don't NEED a different media pH, which is much less important in container culture than it is in the garden. I've puzzled over how to answer the question in a way that's easy to understand, because it's a complicated question. First, pH affects mostly the solubility of essential micro-nutrients and other nonessential elements that can become toxic, once certain pH levels are reached.

Basically, in mineral (garden) soils, the micro-nutrients are already IN the soil, and the ideal pH is a happy medium where all the elements are in a favorable part of their availability range. Too much deviation either upward or downward in the pH level can have a significant impact on availability and toxicities.

In container media, the organic components contain only very small amounts of micro-nutrients, locked securely in the hydrocarbon chains of the medium. So, raising or lowering the pH of the medium or the soil solution has little impact on the availability of these nutrients.

If you point to a pH induced Fe deficiency and say Hey, look here - a pH induced deficiency", I'll point to the fact that technically it's not a function of the pH, but of the presence of high concentrations of Ca, Mg, Na, or bicarbonates, with the increase in pH being only the symptom.

If you could use a medium that is devoid of potential toxicities, and has all the essential nutrients in the right ratio, you can grow most plants very well (in container media) at pH ranges from 3.0 to about 8.5.

Here, you'll see the standard pH chart for mineral soils, depicting availability throughout the pH range. You can see that 6.5 to 7.0 is pretty favorable:
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This is a pH chart, also pretty standard, showing a different picture for container media:

Al

Thanks Al, very interesting chart. I may try to keep things closer to 5.0-5.5 in containers, now that I see that chart.

I know this is an old thread but I'm trying not to ask a question that was already answered 20 times.

When measuring the ph of my 5-1-1 mix with no lime added, I got readings from 4.5 to 5.5 with careful cleaning of notoriously unreliable PH meter.

What should the average PH of the 5-1-1 mix be without lime?

I just planted okinawan purple sweet potato vines in 18 gallon rubbermaid rectangular containers. I read sweet potatoes optimum PH is 5.3 to 6.5, yet another article said 5 to 6. Regardless, should I add a little bit of lime since I am getting readings below 5?

Reading above info would suggest this possible lower ph is not a big deal but I ended up paying $5 per slip of these and want to be sure.

IMO either way you would probably be OK as far as the pH goes. The pH will probably raise a little over time anyway. I had some similar concerns regarding potatoes in a limeless mix, and it was suggested to me to make sure that they get enough calcium and magnesium since there is no lime.