Soil pH in blueberry plants
Learn the importance of growing blueberries in a site with an acidic soil that meets the blueberry plant’s pH requirements.
Lowering a soil's pH to the desirable blueberry range of 4.2-5.0 can be a challenge if its pH is 7.0 or more. It is best to start by selecting a site with an acidic soil that already meets the blueberry's pH requirements.
Acidifying soils with a starting pH greater than 7 is very difficult because:
- These soils have a higher buffering capacity. This means they strongly resist any pH changes. Any changes would be short lived and the pH would soon return to where it started.
- They often contain calcium and magnesium carbonates. These "free carbonates" will react with the acidifying amendments, neutralizing them and prevent any lowering of the pH.
- On slightly acidic soils with pH values below 6.5, it is possible to acidify them by adding sulphur or ammonium sulphate. However, be aware that not all sulphur containing fertilizers are affective in lowering pH.
Elemental sulphur is the most economical way to lower a pH in these slightly acidic soils. Its effectiveness depends on:
- Incorporation into the soil.
- An active sulphur bacteria population in the soil. These specific bacteria convert the sulphur to sulphate, SO42-. As a result of this conversion process a soil is acidified.
- Time, so plan ahead. It is a slow process, taking 3-12 months to complete depending on soil temperature and moisture.
- Annual sulphur applications that may be required to maintain the lower pH
The amount of elemental sulphur required to lower pH is influenced by soil texture. OMAF and MRA guideline for lowering pH using elemental sulphur is listed the table below.
| Soil texture | For each 1.0 pH unit | For each 0.1 pH unit |
|---|---|---|
| Sand | 350 | 35 |
| Sandy loam | 750 | 75 |
| Loam | 1,100 | 110 |
For example lowering a pH of 6.0 to 5.0 in a loam soil would require 1,100 kg elemental sulphur per ha.
Iron, aluminum and ammonium sulphate fertilizers may also acidfy the soil but the acidification process is slow. They are not as effective as elemental sulphur.
Sulphuric acid is sometimes suggested as an alternative to elemental sulphur. While it may quickly acidify it has several limitations: (1) it is very dangerous to handle, (2) requires special equipment, (3) its effects are temporary, and (4) it requires large volumes to lower the bulk soil pH. Injecting low concentrations through a drip line will not have a significant effect on the bulk soil pH.
Other sulphate fertilizers such as potassium, magnesium, calcium, zinc or manganese will not acidify soils. These fertilizers have no effect on a soil pH.