This is a partial and incomplete explanation. Since plants don't have legs, fins, or wings, they must grow where they are rooted. If a seed germinated in pH neutral soil, and the pH drops due to, say, 6 inches of volcanic ash, the plant must adapt or die. The Ericaceous family of plants, which includes rhododendrons, blueberries, azaleas, and heather, is adapted to acidic soils, where the pH value would measure more than 4, and less than 7. To my knowledge, all of these plants live in association with mycorrhizal fungi, which are also adapted to grow in acidic soil. With blueberries, the plants fail to absorb iron when the soil pH is too high, and the leaves develop yellowing between the veins, which is termed "iron chlorosis". I don't know if this condition is due to poor iron uptake at the root, or poor iron uptake at the fungi. Fungi are thought to rob the plant of carbohydrate, and supply the plant with nutrients from the soil.

Your soils pH has some affect on the ability of a plant to uptake nutrients. However, some plants have evolved to grow in fairly acidic soils, Blueberries, Rhododendrons, heaths and heathers, but most do best in slightly acidic (6.2 to 6.8 pH) soils and that range is where most all nutrients are mostly available. There are some few plants that have evolved growing in more alkaline soils but even these do not do well in soils with a pH much higher than 7.5, mostly because most nutrients get tied up and are not readily available to the plants.

In order for plants to take up nutrients they must go into solution. That is, they must dissolve so that the plant roots can take them up along with water.

If the pH is too high (aka "alkaline", the opposite of acidic) plant nutrients, especially metals like zinc, manganese, copper, and iron, don't dissolve and are in relatively large chunks or "precipitate". The plant roots have tiny little holes and these large chunks physically can't move into the roots. It would be like you trying to eat an orange through a straw.

When the pH is too low, (acidic) then you get too much of a good thing. If too much of the plant nutrients in the soil go into solution, you get an overdose and end up with toxicity issues. One of the biggest players in toxicity secondary to low pH is aluminum.

As mentioned above, some plants are adapted better to one condition or the other but must plants like the soil to be slightly acid but can tolerate a relatively wide range of pH values.

Also as mentioned above, beneficial microbes that process organic material into plant available nutrients function best within a certain pH range and are less effective at very high or low pH values.

Cool. Thanks for the info!

How does Hollytone lower a ph....which ingredient?

And the 4-3-3...is that percentage of N K P per 1 serving?

So garg, is the common sign of too much acidity in vegetables, yellowing and failure to grow, actually N deprivation because elements such as aluminum have displaced it from the solution?

Aluminum is toxic to (most) plants and humans.

It doesn't effect N availability very much, but it effects root growth a whole lot. The root tips and membranes "burn" unless the plant has a tolerance to the aluminum. Rather than "burn" I guess I should say it prevents cell division/transport.

In higher pH soils in a lot of areas, there's generally just as much aluminum in the soil...it's just in forms that are plant unavailable.

Someone in florida was telling me that the higher ph soils have big problems with aluminum.

1) Yeah, what nc-crn said.
2) Someone is Florida is confused. That is, unless, they were talking about not enough aluminum. That's not very common unless your triangle palm isn't blue or your blue hydrangeas are turning pink.

This post was edited by gargwarb on Fri, Mar 29, 13 at 10:43

But consider, for example, the same plant in pH=5.5 and pH=7.5 soils. There is a difference in certain ions availability of a factor 100. That same plant does or does not change any micro-physical or chemical characteristics of its roots?

Actually come to think it was said in regard to high CEC, such as the muck soils of florida.

But that is also odd, because higher CEC would generally correlate with higher ph. Below is a UF page about aluminum in sandy soil.

Here is a link that might be useful: as well as EC