Established Blueberry Fertilization and Tissue Testing

Gordon Johnson, Extension Vegetable & Fruit Specialist;

For established blueberries check the soil pH twice a year. Take a random composite 6-8 inch sample from the soil under the mulch in the spring and again in the fall. The pH should stay between 4.5 and 5.0. Sulfur should be added to lower the pH if it is above 5.0 or lime should be added to raise the pH if it has dropped below 4.2.

Apply nitrogen (N) in 2 applications every year to total 60-80 lbs of actual N. Apply 150-200 lbs/acre of ammonium sulfate if pH is above 4.8 or 70-90 lbs/a urea if pH is below 4.8 at bud break. Apply the same amount again 4 weeks later.  Additional N may be needed based on tissue tests. If a fertilizer injector is being used, the nitrogen can be split into smaller applications over the 6-8 week period after bud break when new growth is being produced.

P, K, Ca, Mg, and micronutrient additions in established blueberries should be based on tissue tests. Tissue tests are important tools for monitoring blueberry fertility. Leaf samples should be collected from mature leaves in the mid-portion of current season’s growth the first two weeks after last harvest in July or August. A double hand full of leaves should be harvested from across the field, washed in tap water, dried and sent to a testing laboratory. Below are critical nutrient ranges for blueberries.

Nitrogen (N) 1.7-2.1 % with normal at 1.9 %

Phosphorus (P) 0.06-0.18 % with normal at 0.1 %

Potassium (K) 0.4-0.65 % with normal at 0.55 %

Calcium (Ca) 0.4-0.8 % with normal at 0.6 %

Magnesium (Mg) 0.2-0.3 % with normal at 0.25 %

Iron (Fe) 70-300 ppm with normal at 200 ppm

Manganese (Mn) 50-500 ppm with normal at 250 ppm

Zinc (Zn) 15-30 ppm with normal at 25 ppm

Copper (Cu) 5-15 ppm with normal at 11 ppm

Boron (B) 30-50 ppm with normal at 40 ppm

If levels are below these ranges then the plant is deficient. If deficiencies are found, use the following recommendations:

  • Low N (if N is below 1.7 percent): Increase rate of N application by 10 percent for each 0.1 percent that sample is below desired level. If soil pH is above 4.8, use ammonium sulfate; if below 4.8, use urea. Apply half of the nitrogen fertilizer at bud break and the remaining half four weeks later.
  • Low P (below 0.06 percent): Apply 180 pounds per acre superphosphate (45 percent P2O5) at any time.
  • Low K (below 0.40 percent): Apply 400 pounds per acre potassium magnesium sulfate (K-mag) or 160 pounds per acre potassium sulfate in fall or early spring.
  • Low Ca (below 0.4 percent): Refer to soil test and apply lime as needed if soil pH is below 4.0. Apply 1,000 pounds per acre calcium sulfate in fall or early spring if pH is above 4.0.
  • Low Mg (below 0.2 percent): Refer to soil test and apply dolomitic limestone if pH is below 4.0. If pH is above 4.0, apply 250 pounds per acre magnesium sulfate or use potassium magnesium sulfate (K-mag) at 400 pounds per acre if K is also low. Apply in fall or early spring.
  • Low Mn (below 50 ppm): Apply a foliar spray of manganese chelate at 6 pounds per 100 gallons per acre twice during the growing season. If product label offers a different recommendation, follow label recommendation.
  • Low Fe (below 70 ppm): Apply a foliar spray of iron chelate at 6 pounds per 100 gallons per acre in late summer and again after bloom the following year, but check product label and follow its recommendation.

This information was taken, in part, from the Mid-Atlantic Berry Guide