Understanding your soil pH

Tomatoes will grow in a wide variety of soil types and across a wide range of pHs although they prefer a pH between 5.5 – 6.8.In order to understand your soil type it is essential that you have an understanding of what pH is and how it may affect the nutrition of your tomatoes.

The term pH defines whether your soil, is acid or alkaline. The pH scale runs from 0 – 14 with 7 being neutral. Numbers below 7 indicate acidity and above 7 alkaline. Most soils have a pH in the range 4.5 to 8.5. Tomatoes enjoy a slightly acid soil usually with a pH around 6.5.

The availability (uptake of nutrients from the soil by the plant) of nutrients is affected by soil pH. This is amply demonstrated by the chart below.

This shows that most nutrients have greater availability at pHs around 5.5 – 6. pHs can be adjusted : lime will make the soil more alkaline and whilst making the soil more acid is more difficult, usually sulfate-based fertilizers (eg sulphate of ammonia) and acidic organic material will help.

Testing soil pH can be done simply by mixing soil and water and testing it using a pH meter, testing kit or litmus paper.