Liming the Soil:
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Many people talk about adding lime to the soil, and it has been widely practised for many years, yet the reasons for doing it are often not fully understood. Adding lime to the soil helps to get the balance between the soil’s acidity and alkalinity, measured on the PH scale ranging from 1 (highly acid) to 14 (highly alkaline). A PH of 7 is neutral and the optimum for most vegetables. In soils with a PH outside this range plants may show signs of nutrient deficiency. In acid soils nitrogen, potassium and magnesium all become less readily available to plants, while in alkaline soils phosphorus is reduced. Adding lime to an acidic soil can help to restore this balance, while at the same time providing an important source of calcium.
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Liming can also indirectly help the soil structure. By improving root development and raising the numbers of micro-organisms, the crumb structure of the soil is improved, therefore improving the performance of your plants. A final plus-point for lime is that it can help prevent diseases such as clubroot in the brassicas, and because brassicas generally prefer slightly alkaline conditions, liming these areas can be beneficial.
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However, you should lime your soil only if its PH is below 6.5. If you do need it, it should be applied in autumn, just before digging the soil over. It should not be applied at the same time as you add organic matter or fertilizers.