Monday, 23 February 2009

Let's Talk Lime

There's one topic that all too easy to overlook, and that's LIME. I admit to not paying enough attention to the subject, and judging from my activities yesterday I have suffered for this neglect. Liming isn't fun. Best done in the Autumn or Winter it's too scientific for some and yet I find it fraught with uncertainty.

To get to business: How is one to know how much lime to apply to your plot?

1. Establish the current pH

2. Calculate the dosage

3. Apply it

1. There is a fiddly procedure requiring chemicals and test tubes
followed by a rather subjective colour comparison. Alternatively there
is a more expensive metre. Like all meters it is only as good as the
calibration. When I read the following I felt that sinking feeling "
Sorrel, creeping buttercup, nettle, dock and mare's tail are all signs
your soil is becoming or is too acid" But at least that was advice for free. All the same I feel the need to get a meter - and to use it for a systematic survey of the plot this year. (Yes I should have done this last autumn)

2. Here's the difficult part. How much do I need to raise the pH by 1?

The back of the packet the meter came in says 300g per sq m (10.5 oz per sq yard)

Several guides say 275g - 850g (0.5 to 1.5 lb)

The lime sack (J Arthur Bower's Garden Lime) says 100-200g (3-6 oz)

So all in all there are vagaries about both the assessment of the pH and the dosage required.

3. Now the fun: spreading it over the surface and raking it in. Don't do this on a windy day (That ruled out last weekend). Who has a weighing scales at their allotment??? And what if your lime sack has absorbed water (as has happened to me) Answer - Calculate how much you need to apply for the whole area you want to treat as a proportion of the full bag of lime you have and do your best spread that amount as evenly as possible over the area. It is not an exact science, but you won't be far off the mark. You'll do a lot more good than the harm you do when you don't get around to doing this task for another year.

The lower case 'p' stands for "potenz" (potential) and the upper case 'H' stands for Hydrogen. So it's 'pH'. Besides PH is public house.

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