The Right Soil pH for Potatoes

by Annette Welsford 3 Comments

Soils with a pH lower than 6.5 are best-suited for raising potatoes; the ideal soil pH for potatoes is 5 to 6. In fact, potatoes are one of the few vegetable crops that can tolerate and thrive in more acidic soils — soils in the 4.8 to 6.0 pH range. Potatoes may not do well in soils with a pH higher than 7, because if the pH level is high, many of the nutrients that potatoes require to grow will not be available.

How to Check the pH

The cheapest way of doing this is to use a swimming pool test kit or a piece of litmus paper. Proper pH meters are easy to use and are available from many nurseries, but they are usually expensive for home garden use.test soil pH

The most common pH test involves taking a small soil sample (about 1 teaspoonful) and mixing it with a small amount of chemical (provided), then sprinkling the mixture with the special powder provided. The powder will change colour and you then match the colour of your sample with the colour on the card included in the kit. The card will tell you what pH level the colour indicates.

How to Lower pH

To lower your soil pH, add agricultural sulphur (available at garden centres).

  • For sandy soil, use 25 grams per square metre.
  • For loamy soil, 50-70 grams per square metre.
  • For clay soil, use 100 grams per square metre.

These amounts will lower the pH of the top 10 cm by about 1 pH unit.

How to Increase pH

If you need to increase your soil pH, then you will need to add agricultural lime. It is ideal if this can be incorporated, and this should ideally be done about a month prior to planting.

For comprehensive step by step instructions on preparing your soil, refer to Chapter 6 of our book How to Grow Great Potatoes.

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