Re: pH level and suitable plants.

"Peter Jason" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> Is pH all that critical for plant growth?

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
> 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.

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.