What's It For? - Lime
Soil is limed as and when necessary to counteract its natural tendency to become more acidic and to create and maintain optimum conditions for plant growth. Soils may be alkaline (chalk or limestone soils) or acidic (peaty soils) in reaction. An alkaline soil contains lots of calcium - an element required in small amounts by all plants. In very acid soils there is a shortage of calcium salts. The acidity or alkalinity of a soil is measured on the pH scale, which ranges from zero (exceedingly acid) through 7 (neutral) to 14 (exceedingly alkaline). In Britain most soils tend to be slightly acidic due to rain constantly leaching out the calcium. Luckily, most plants will thrive if the acidity of the soil can be adjusted to a compromise pH of 6.0-6.5. Club root disease of brassicas flourishes in acid soils but can usually be controlled if the soil can be held at a pH 7.5 (the upper pH limit for this class of vegetable). Simple soil testing kits, available from garden centres, enable you to determine the pH of your soil. They also give a list of plant pH preferences and the amount of ground limestone that you need to apply to raise the pH by one unit.
It is always preferable to use lime in the form of ground limestone (or chalk), which is safe and easy to apply. Hydrated lime (slaked lime, builder's lime) is available but its caustic nature means that it must be handled with care and applied with care to avoid damaging plants in the vicinity. If possible, apply the lime in autumn or after winter digging so that the rains wash it in slowly. Choose a calm day and spread it evenly by hand. Never use lime at the same time as manure or nitrogenous fertilisers as it may react chemically with them and reduce their effectiveness. If you are in a rush, apply the lime to soil that has been raked to a fine tilth and distribute it by raking well into the top few inches. Water the area and allow it to stand for a week before applying a nitrogenous fertiliser.
Information can be obtained from the TradingHut on Sunday mornings from 10.30am to 12 noon.