pH level and suitable plants.

Is pH all that critical for plant growth? I have had varying results planting this and that, so perhaps I should measure the pH of the soil. How is this done? If I get a certain pH, is there an index listing all suitable plants for that pH? Are buffers necessary too.
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How
suitable
You can purchase soil pH testing kits at most garden centers and nurseries. Not wonderfully accurate, but close enough. You should take samples in various parts of your garden, as it can vary from location to location.
It is desirable for the largest range of plants to have a soil pH that is slightly acidic - 6.0 to 6.5 is right in there. Too much variation in either direction and you significantly reduce the number of plants you can grow. The primary problem is soil pH is impossible to change permanently and difficult to change significantly in either direction.
Most plants will tolerate a range of soil pH, with slightly acidic soil (as I already mentioned) being the preferred choice. Most veggies, which prefer neutral to slightly alkaline soil, are the largest exception and they can be accommodated by groiwn in raised beds where you can add new soil with the chemistry you need.
Best to get a test kit and see what you have to work with. Then report back and we can provide more specifics about amending the soil or suggesting appropriate plants.
pam - gardengal
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Hugely so *for some plants*; others are much more tolerant. Azealeas, rhododendrons, heathers, camelias for example are said to demand acid (low pH) conditions. You can buy 'ericaceous' composts which are designed for them. Some other plants, saxifrages, quite a lot of other alpines, *demand* alkaline conditions & usually originate from calcareous rock areas.
Some of this at least is to do with how many handle their need for iron. The 'acid loving' plants cannot absorb enough iron in the presence of carbonate containing (usually calcium carbonate, chalk, limestone) growing medium. They are sometimes called 'calcifuge'; but in many cases its not so much that they cannot stand the calcium/high pH, its that they cannot get enough iron. Provide the iron as 'chelated' iron, which prodects it from the carbonate, & the plants *will* grow. You can buy chelated iron (pronounced kellated) easily. (Iron ions react with carbonate ions to form very insoluble iron carbonate, siderite I think?, which the plants cannot use.)
Those requiring lots of calcium however do just want it & will not grow without it, & so demand high pH, lots of limestone etc. I even use limestone chippings to cover the drainage hole in pots for these, not just a few stones.
>I have had varying results

How
suitable
You can measure it with a pH meter with a soil probe, garden centres sell them. Or by shaking a defined amount of soil with pure water, decant clear liquid & add a coloured 'indicator', the colour tells you the pH. Bit messy & needs some care; garden centres sell kits.
Many books will tell you if the plant demands high/low pH. If it doesnt say its probably, within reason, non critical. Soil tends to have buffer tendencies of its own, its quite hard to shift the pH permanently without big additions of peat, leafmould etc (down) or lime & chipped limestone (up.)
Is your problem pH? Depends what you are growing. If its some of the pH intolerant plants, could well be. If more run of the mill stuff, probably not unless for some reason the pH is rather extreme.
H.
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To Harvey You did an excellent write up.
Gary

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