It is generally easier to make soils more alkaline (i.e. increasing the pH) than it is to make them more acid (i.e. reducing the pH). A movement of 0.5 is quite easy but, because the pH scale is logarithmic, a movement of say, 2.0 points becomes difficult because there is a factor of 10x between each full point, so pH 5.0 is actually 100 times more acid than pH 7.0. Also, different soil types react in different ways to the application of lime. To achieve the same result, clay soils and peaty soils require more lime than do sandy soils. To increase your pH by 1.0 point and make your soil more alkaline. pH ALTERATION TABLE Amount of lime to apply in ounces per square yard Your Soil Type Organic Matter content Using Hydrated Lime Using Chalk or Ground Limestone Sandy Soils Medium 4 5 Low 3 4 Medium Loam Soils High 16 21.5 Medium 8 10.75 Low 6 8 Clay soils High 20 27 Medium 12 16 Low 9 12 Peat, Moss or Fen soils High 25 35 NOTE: Applications in excess of 20 oz per square yard must be split Applications in excess of 20 oz per square yard are best provided by splitting the job into two equal applications which are spaced at least six months apart, putting on half the total amount on each occasion. It is quite safe to apply amounts of less than 20 oz per square yard as one dressing, preferably in the autumn, and this should be incorporated into the soil by digging. Hydrated lime should be available from sundriesmen, garden centres or builders merchants. Some safety precautions such as gloves and goggles to keep the powder off exposed skin and out of eyes would be sensible, and of course you should always follow the instructions on the packaging. Ground limestone is less fine and flyaway. Correction of an over acid soil should be considered as a longer term job than just one year, and it is advisable to test your soil each year if a large alteration is planned over several years.

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How pH affects plant foods  | Finding out your pH | Raising your soil pH  | Lowering your soil pH | Types of lime explained. | Plant preference lists

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