How do you make acidic potting soil (for blueberries)

I've successfully struck blueberry cuttings and I'll need to put them up in a few months time.

Acidic potting mix costs about $12 a bag (20 litres/ 5 quarts). If I get a dozen cuttings then that's over $100, which I don't want to pay.

So far I have:

- free homemade compost.
- free horse manure.
- maybe I can get free seaweed if I drive to the ocean.

But I don't know what I should add or buy to make it sufficiently acidic. Any suggestions?

My family owns blueberry farms in the Appalachian mountains, the soil is very claylike but the berries have always done fantastic just planted on 1" mounds in rows and ammonia based fertilizer. Berries the size of quarters

Apparently compost has a tendency to lower pH, so that might be enough. Seaweed is good for micronutrients I've heard, so might be worth gathering some but I'd be wary of the salt content. Some places mention using well-rotted manure to lower pH as well. bottom line, I'd wait to see how the cuttings do before taking any more steps to change pH.

like was a mentioned grow on mounds with half compost and pure peat moss. that should make it plenty acidic. if a few years down the road they start getting red leaves, you may need to amend with a ring of sulfur every other year to keep ph down but thats only if you don't have acidic soil to begin with. a soil test could tell you for sure.