pH and Eh is huge when it comes to nutrient availability. You do want a sweet spot for all nutrients to be available. If you go too high, some nutrients are completely blocked out, if you go too low, you can have toxicity or lockout as well.
Eh is the one most don’t know about and it affects nutrient availability as well, even if pH is correct. But it’s a more complicated subject and harder for people to monitor. You need to go more by growing practice for this one. The type of nutrients used affects it greatly as well as watering consistency.
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One reason plants do better with rain water is because the pH is ideal, another reason is because it isn’t full of minerals. It allows soil nutrients to become water soluble and then plant available.
pH matters most for chemical inputs than it does for organic ones. So that is where much of the concern comes from with hydroponics and with cannabis growers.
All of that said, I do not buffer my water. It’s too much work, especially for the amount of trees I have. I have well water with a high pH, so I have no problem adding more acidic inputs for nutrients. Most people have water with a high pH, it’s just certain areas where it can be lower.
It is better for the pH to be kept consistent than to constantly alter it. The reason being is that plants will adapt to the environment they are put in. Their root exudates affect the pH around the root system. If we keep changing it, the plant cannot effectively adapt.
I try to be aware of the pH more for my foliar sprays than for watering. Though I would totally install a garden RO system for watering if I could. It just isn’t feasible here being in a drought area on a well.