Coppice Road Allotments Association

(affiliated to the National Society of Allotment and Leisure Gardeners Ltd)

© C.R.A.A. 2008-17

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12 May, 2018

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The diagram (left) shows the solubility of plant nutrients at different pH levels. The broader the band, the greater the solubility and the greater availability for use by the plant.

The solubility of most nutrients declines rapidly below pH 5.0, while others show a reduction above pH 7.0.

To ensure a ready supply of all nutrients, for most plants, pH levels should lie between pH 5.5 and pH 6.5.

It should be remembered that peat and peat-based composts, although registering a pH of around 5.8, actually behave as though the pH is 6.5, owing to its ‘buffering’ capacity.

A pH of 6.0 will provide all nutrients in an available form for most plants to assimilate optimum levels. Some plants are adapted to succeed at pH levels outside this band (e.g. Blueberry), while others will tolerate levels of greater extremes.

Adding fertilisers to a soil which is already too acid (below 5.5) will actually render them less soluble and less available for use, and thus would be wasteful and ineffective. Raising the pH, by the addition of lime, will actually increase the solubility of those nutrients already present and may reduce the levels of fertiliser to be added or obviate the need to add them entirely.

Use of Lime to adjust pH >