Mar 26, 2013
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United Kingdom
I have often extolled the virtues of woodash as an organic fertiliser, especially on fruiting plants, (inc. tomatoes, peppers, cucurbits, aubergines, etc) potatoes and onions, but I see warning after warning regarding its liming effect, so this post is to put that into perspective.

When I suggest usage, what I mean is a good dusting, often in conjunction with organic matter which is still rotting, that rot being an acidic process.
It is also the case that most vegetable matter is very slightly alkaline, so removing it to eat very slightly lowers the pH.

The application rate for garden lime, dependant upon your soil, to bring the pH up from pH 6.0 to pH 6.5, is between 14oz. and 18oz. p.sq.yd. and that the higher your soil pH. the more lime required to raise pH. by 0.5.
If you take into account that woodash has half the liming effect of garden lime, then, in order to raise the pH by 0.5, you'd have to add approx. 2lb per square yard, (1kg/sq.m.)!!!

Remembering also how light woodash is, and that adding three handfuls p.sq.yd. probably equates to 4-6oz, you can see both, 1) the ridiculous extent to which you'd have to use it to cause problems, and 2) the benefits, as far as the veg garden is concerned, of replacing lost alkalinity.

So don't shovel it on, but applied like fish, blood & bone, it's an excellent weapon in the organic armoury.

If you have problems with soil alkalinity, it is extremely unlikely that they were caused by woodash.
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Oct 8, 2017
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Birmingham Alabama
Hardiness Zone
United States
I will see your wood ash and raise you a red cabbage, which when pulverized in a blender and doused with boiling water will deliver a 7ph neutral purplish dye that can be soaked and dried into paper, allowing for a homemade ph test that would at least suggest either a go or no go for the need of liming.

A very acidic solution will turn the dye a red color. Neutrals result in a purplish color. higher ph appears in greenish-yellow.