Blueberries generally will tolerate temperatures to -20°F, although varieties vary somewhat. Most require 750 hours of chilling below 45°F. In Pennsylvania, this requirement is met usually by no later than early February. After the chilling requirement is met, the plant loses its dormancy and thus its cold hardiness with each warm period, making it increasingly susceptible to cold injury as the season progresses.
The best soils for blueberries are moist, porous, and acid. The soil pH should be between 4.5 and 5.0. A lower pH can result in manganese or aluminum toxicity, while a higher pH results in the unavailability of certain nutrients, most notably iron. In southern New Jersey and Michigan, where much commercial blueberry production is located, blueberries are grown on very sandy soils in areas where the water table is very shallow. Many parts of Pennsylvania do not have these very light soils, so soils usually need to be amended.
In the year before planting, eliminate all noxious weeds, increase soil organic matter by compost application and/or cover crops, and test the soil. Soil test kits are available from county extension offices. Amend the soil according to test recommendations. The effects of sulfur (to lower the soil pH) and phosphorus (if needed) require time, so these materials should be added in the fall before planting. Potassium can be added either in the fall or when nitrogen is applied in the spring. Do not plant blueberry plants in high-pH soils without amending them first! Because sulfur does not move readily through the soil, surface sulfur applications after the plants are in place are ineffective in lowering the pH, and the plants will not thrive.
Irrigation and Mulch
Because the blueberry plant is very sensitive to fluctuating soil moisture, mulch and irrigation are essential for a healthy planting and consistent yields. Plants should be kept well watered, especially during hot spells in the summer. Hardwood bark mulch (such as that used for landscaping) and rotted sawdust are good mulches. Mulch should be applied to a depth of 4 inches and replenished whenever necessary. Avoid mulches with a high pH such as mushroom compost or noncomposted leaves, which may be high in natural toxins.