Lime weights for no man

[melbee]

Hi
it might seem a daft question but how much granulated lime would I have to add to a 5 litre   plantpot of peat to make the compost  neutral or slightly alkaline .Teaspoon and table spoon measurements only please

Mel

[Maggi Young]

Mel, I have no idea, but why would you want to?
If you have peat then use it for plants which appreciate a more acid environment.
There has to be an easier way to get a neutral or more alkaline medium than by trying to adjust the ph of peat??!!

[melbee]

told you it was a daft question . .Let me ask it in a different way .I have used those soil acid alkaline  test kits and found the results doubtful .What I am after is a compost that is soft strong and thoroughly absorbant . :)I am after a formula .Something like two parts peat, one part sand, two loam , is alkaline .It does not have to have peat in it .I am just after a mix that is a known quantity on the acid alkaline scale .Although if there is a standard mix I would like one that is neutral to slightly alkaline .

A slightly more extreme compost would be take the contents of one car battery and mix with a kilo of peat,  that compost will be acid .Take one bag of builders lime stir in some chalk, that compost will be  alkaline . I am looking for some middle ground

Pheeeeeew the more I write the worse it sounds .I hope I am starting to make sense 
Thanks
Mel

[Giles]

Given where you said you lived, in one of your other postings, the simple answer would be: Don't bother with lime, just water the pot with tap water  
(I have Anglian Water too   )
The 'correct' answer would be difficult to work out, as it depends not only on the original pH of the peat (which you would need to measure; my last batch of Irish Moss Peat was about ph 5.5), but the neutralising value of the particular type of lime you are applying, and the buffering capacity of the peat as well (the peat's ability to 'mop up' the alkalinity you are applying).
It is explained on the RHS website:  http://www.rhs.org.uk/advicesearch/Profile.aspx?pid=144
Even if you worked it all out, there is still the potential for getting it wrong (believe me!)
I would buy a pH testing kit, and work away at it gradually, adding a little lime at a time over a few year or so.
Something like limestone chips are pretty idiot proof (as they take ages to dissolve, and you can always pick them out at repotting) but if you add something like hydrated lime you can cause sudden rises in pH, burn plant roots and it's difficult to reverse an 'overdose'.
It might be easier to buy a combined fertilizer preparation, available from somewhere like 'GardenDirect' for turning 'peat' into 'multipurpose compost'.

A politically correct response, might be to ask why you are using peat, anyway.I use peat specifically to acidify. If you don't want to acidify, use something else.

[ichristie]

Hi Mel, I notice you stay in Cambridgeshire so you should be able to but fairly good John Inness ready mixed copost soil based. I would also suggest that you go to a decent garden shop and buy some dolomite lime not the hot granulated stuff, the J.I should be in 25 /30 ltr bags add 50% chippings 50% peat then fill one 9cm (4inch) square pot full of dolomite lime mix well then test it should be about 7.  The only thing is that some J/I composts differ depending on where the soil comes from so maybe test first the adjust the lime to add.  cheers Ian the Christie kind

[Giles]

...sorry the link didn't work..on the RHS website, just search on 'soil ph' and you will find it.

[melbee]

Hi
thanks for the links I will chase them up .
A formula .ahhhhhhhhhhhhhh just what I have been looking for .I am getting closer .Thanks for that Ian
It make me sound like that scientist with the welding goggles on with the two  brass electrodes above his head and the gigantic spark arcing across 
Regards
Mel

[Rodger Whitlock]

I use a peaty-silty lake bed sediment as the basis for my own potting mix. A 30-liter bag needs about 35 g of calcium carbonate (ground limestone, ground chalk, "agricultural lime") for every half pH unit it is below chemical neutrality, pH=7, to bring it up to pH 6.5.

These limes typically have a density about 2 g/ml.

I will leave the arithmetical details as an exercise, in part because I don't know what pH your mix already is, in part because it's good for you.

However, if pH is critical, I suggest you buy some proper test strips sold by chemical supply houses. Your nearest university chemistry department may be able to help you out. The test kits sold in garden centres are, frankly, toys.

[Giles]

..if you wanted test strips, I've a box of them, which I never use.

[melbee]

Hi

When you say test strips .Are they test strips like litmus paper .What method is used .Is it dissolve the compost in a container and stick the strip in and see what colour it turns?
Mel

[Rodger Whitlock]

When you say test strips .Are they test strips like litmus paper .What method is used .Is it dissolve the compost in a container and stick the strip in and see what colour it turns?

Just like litmus paper, but containing more than one indicator, sometimes mixed, sometimes in separate spots. They come in both narrow-range and wide-range versions. If you buy narrow-range pH test strips, you must get the right range. Horticulturally significant pH ranges from about 4.0 (blueberries) to about 7.5.

My own supply (left over from my days as a chemist) includes a full-range pH 1-14 and three narrow-range versions, pH 3.5-5.5, 6-8.5, & 5-10. None of these are ideal for the purpose, but together they pinpoint the pH to half a unit - more than good enough for horticultural. purposes.

You understand the method.

A packet of 100 test strips will last a lifetime.

[Giles]

-yes, just like Roger's, 3 squares on each strip.
Mine cover pH 5 - 10. I personally don't like them (the colours aren't very pretty  ), but they do give consistent results.
The whole box, about the size of a match box, so easy to post. If you would like them, pm me your address.

[melbee]

Hi Giles
thank you very much for the litmus strips they are just what I am looking for .They arrived this morning .I tested them out on a bag of soil based seed compost that I got this afternoon they were very accurate

Thanks again
Mel

[Giles]

 

[iann]

There really is no answer to the question.  Peat and limestone are both solids and only have a pH in solution with water.  The pH of a solution made at any one time may be acid or alkaline depending on how quickly the components of peat and lime dissolve and then react with eachother.  This will vary over time until eventually one or other is more or less exhausted and the pH will swing towards acid or alkaline.  By this time you will probably have a pot full of mush and have repotted your plant

As some have suggested, I wouldn't start with peat and try to get an alkaline compost, it is just fraught with problems.  That said, most bags of commercial potting soil are mostly peat with enough limestone powder to take the pH somewhere near the 6-7 range.  Even then the pH at any one time will vary as the ingredients react together, something that isn't commonly appreciated.  You might want to start from there and nudge it just a little further.

John Innes suffers from the same problems but less so, because there's less peat and so less lime.  Modern JI mixes also tend to have very finely shredded peat and don't rely on it for their structure so you hardly notice if it reacts with the lime and collapses.

I also suggest you don't panic about the exact pH.  It is difficult to overdo the limestone provided that you use a fairly hard grit and not a fine powder or something soft like oyster shell that would react very quickly.  And as suggested, do consider the water you use.  Over time, hard water will dominate the original soil chemistry anyway.