What Should I Add to the Soil for Blueberry Bushes?

Optimal Growing Conditions for Blueberries

• Blueberries grow best in a soil with a pH of 4.5 to 5.0. A lower pH can be adjusted with dolomithic limestone, but most people will find that their site has a pH that is too high. In that case, the soil where the blueberry bush will be planted will need to have acid added. Your local university extension can perform a soil test for you, or you can use a pH meter to test the pH yourself. You will need to know the pH of your soil before attempting any amendment.

Ammending the Soil

• Blueberries prefer soil with high levels of organic matter. Begin your site prep by amending the soil with at least 8 inches of Canadian peat or loose compost. Rotted sawdust, leaf mold, cottonseed meal or feather meal also make good components for amendment, though they should be mixed with peat or compost. Canadian peat is best, where available, because of its low pH.

Acidifying Soil

• Check the pH of your amended soil before applying acidifying compounds to the blueberry soil, as precision is important -- blueberries thrive in a rather narrow band of acidic soil. A report from your local university extension will tell you how much of each acidifying compound needs to be added to the soil to best suit blueberries. The most commonly used compounds are elemental sulfur, aluminum sulfate and iron sulfate. Iron sulfate tends to act fastest to acidify the soil but is significantly more expensive. Aluminum sulfate is falling out of favor because misapplication can damage plant roots.

Fertilizing and Re-acidifying Existing Bushes

• Fertilization is often needed a few years after the blueberry bush is established. Apply a fertilizer designed for acidic plants, such as rhododendrons, within a foot of the plant, being careful not to splash the crown. The most important nutrient for blueberries is nitrogen. If yearly soil tests reveal that the soil needs to be acidified as well as fertilized, it is possible to re-acidify the plant by digging four holes at least 1 foot deep and 4 inches in diameter at the edge of the roots of the plants (12 to 18 inches from the crown of the plant). Mix 1/4 cup of elemental sulfur with the soil removed from the hole to restore acidity to the plant; add 2 or 3 tbsp. of iron if the plant is also iron deficient. Replace the soil in the holes you've dug and keep the plant moist.