The range of garden soils is given by the RHS as 4-8 though some books go to 8.5.
State why 6.5 is the most suitable pH for a wide range of plants in the British Isles.
Normally: Plant growth of a great range of plants is good in the range of 6→7.5; A good pH for most gardens is 6.5 as it suits “most plants” and most plant nutrients are readily available (this alters slightly according to the soil’s texture). `
Soil Structure (soil organisms, crumb formation): Worms dislike acid soils and so such soils have few worms. Worms secret alginate into the soil that acts as a soil glue creating good soil structure. Calcium products can be used to help break down clay soils chemically, so improving the structure (calcium carbonate and hydroxide will alter the soil pH, calcium sulphate will not). Soils with natural high free lime content (calcareous clay) will not respond to the application of lime products.
Nutrient Availability: See above. Nutrient availability is affected by both soil pH and soil texture.
Lime Induced Chlorosis: Where the free lime in the soil locks up iron and magnesium molecules in the soil and makes them unavailable to the plants. This causes a mineral deficiency with iron showing up as yellow young leaves and magnesium as yellow inter-venial patches on old leaves (treat plants with sequestrene of iron).