Well, I didn’t do myself any favors with my poor tracking of soil pH before planting the blueberries. Between the clay soils and overestimation of the buffering effect of decaying organic matter placed into raised beds, my soils were slightly alkaline at the time of planting in the spring. With fall approaching, it was time to apply sulfur while the soil microbes are still active.

Sulfur is not biologically active as its approval for organic uses may insinuate, but it is literally just an element from the periodic table. It is mined and shipped out in its pure form (if you are lucky enough to find pure sulfur) or in my case, cut with 10% inert fillers.

Now it is time to calculate the application rates which I have discussed before. Below are the tables from that discussion. Ohio State University Extension is the source of the Table 1 while Table 2 is the same but with my calculations converting the application rates from pounds of sulfur per acre to pounds of sulfur per 1000 square feet.

 

Table 1. Rates of elemental sulfur required to decrease soil pH to a depth of 6 inches.
Desired change in pH	Application rate based on soil texture1
	Sand	Silt loam	Clay
	———————– lb S/A ———————-
8.5 to 6.5	370	730	1460
8.0 to 6.5	340	670	1340
7.5 to 6.5	300	600	1200
7.0 to 6.5	180	360	720
8.5 to 5.5	830	1660	3310
8.0 to 5.5	800	1600	3190
7.5 to 5.5	760	1530	3050
7.0 to 5.5	640	1290	2580
1 Assumptions—cation exchange capacity of the sandy loam, silt loam, and clay soil are 5, 10, and 20 meq/100 g, respectively; soils are not calcareous.

 

Table 2. Rates of elemental sulfur required to decrease soil pH to a depth of 6 inches.
Desired change in pH	Application rate based on soil texture1
	Sand	Silt loam	Clay
	———————– lb S/1000 sq. ft ———————-
8.5 to 6.5	8.5	16.8	33.5
8.0 to 6.5	7.8	15.4	30.8
7.5 to 6.5	6.9	13.8	27.5
7.0 to 6.5	4.1	8.3	16.5
8.5 to 5.5	19.1	38.1	76.0
8.0 to 5.5	18.4	36.7	73.2
7.5 to 5.5	17.5	35.1	70
7.0 to 5.5	14.7	29.6	59.2
1 Assumptions—cation exchange capacity of the sandy loam, silt loam, and clay soil are 5, 10, and 20 meq/100 g, respectively; soils are not calcareous.

I’ve brought my blueberry beds from 8.6 to just below 7 with other efforts this year. For that 120 square foot bed, the calculations are as follows:

[Application rate for clay soils to lower pH from 7 to 5.5] * [Area of blueberry bed] / [Area of application rate]

[59.2 pounds] * [120 square feet] / [ 1000 square feet] = 7.1 pounds

Then for the remaining unplanted bed around 8.5 pH:

[Application rate for clay soils to lower pH from 8.5 to 5.5] * [Area of blueberry bed] / [Area of application rate]

[76 pounds] * [120 square feet] / [ 1000 square feet] = 9.1 pounds

So, 16.2 pounds total.

The process:

Buy agricultural sulfur. It was $22/50 pounds at my local feed store.

Weight out the amount needed from the above calculations

Apply sulfur

Give the soil microbes a few months to digest the sulfur and lower the pH

The last picture shows the sulfur on top of the mulch, spread lightly around plants and their active roots while applied more heavily in the spaces between plants, which is only done by necessity. In the unplanted blueberry bed the sulfur was applied evenly to bare soil then covered by mulch.

From this point on, test the soil every year or every other year. Repeat the above process as needed!