Blueberry bushes are relatively easy to grow once the soil has been checked and amended to have the proper pH. Too high or too low and you blueberry bushes will either fail to produce fruit or they will die. It’s easy to modify the soil before the plants go in the ground but what about a few years later? What can you do if the pH fluctuates once the bushes are in the ground?
Ideal Blueberry Soil pH
Blueberry plants prefer an acidic soil. The pH range most desirable for blueberries is 4.5 to 5.0. Assuming you started with this at the time of planting, then adding a simple fertilizer 4 weeks later will help maintain the balance for the first growing season. The mix should be 20-0-10+5 (nitrogen-potassium-phosphate-magnesium). Add 1 ounce around each plant at a distance of 12 to 18 inches from the base.
Determine Existing pH
When dealing with existing blueberry plants, the soil needs to be tested every 3 to 4 years to determine a number of factors. A sample should be taken for testing which can be performed at your local extension office. Not only will the results show any nutritive deficiencies that need attention but it will reveal the pH factor of the soil, which may have changed since the bushes were first planted.
Importance of Testing pH in Acidified Soils
If the soil originally needed to be acidified to accommodate the blueberry plants, the pH levels at different depths may vary, particularly if the acidifying agent was added to the topsoil and not worked in. This can result in the pH being uneven within the bed. Another reason to monitor soil which has been acidified is that it tends to increase in pH levels over time. If it rises too high, it can cause problems for the blueberry plants.
If the soil test reveals a pH of less than 4.0, lime should be added at the rate of 1000 pounds per acre for sandy soil, 2000 pounds for loam and 4000 pounds for muck soils. If the soil test shows a low level of magnesium as well, use dolomitic lime ion the same doses to correct the problem.
If soil tests indicate a pH of 5.5 or above, the pH can be lowered by adding elemental sulphur. This is a little more complicated as the pH combined with the soil type is used to determine the amount of elemental sulphur to add. Sandy soil requires very little while clay soil or soil high in organic matter requires a great deal more. This should be done in accordance with the recommendations made following the soil test as it is more difficult to do after plants are already growing.
After planting, changing the pH is much more difficult than before the plants go into the ground. The best solution is to prepare the planting site 2 years prior to planting and follow a regular testing and fertilization plan. In the event changing the pH after planting is absolutely necessary, the recommendations made by the testing agency should be followed closely.
Michigan State University Extension: Hints on Growing Blueberries
Michigan State University Extension: Managing Blueberries