Soil pH amendments for asparagus, blueberries, blackberries, raspberries

Asked February 6, 2017, 8:49 AM EST

Hello, I live in Laurel, MD and have red clay soil. I recently got a soil test done with the Univ. of Delaware and the results were: pH 5.2, Buffer pH 7.73 (I'm not sure what buffer pH is). P was 11 (low), K was 74 (optimum), Mg was 90 (a little past optimum), Ca was 61 (between medium and optimum). I wanted to plant asparagus. I plan on removing the clay dirt, and mixing in 50% compost and 50% of the original clay dirt back in. Should I not mix that much clay dirt back in? Do I need to add anything else (pearlite?). Some people suggested I completely remove the clay (12x4 feet, 1 ft deep). I was afraid of would act like a container and the roots would only want to stay inside. Should I replace the clay with top soil? Also because the pH of the red clay is 5.2, should I add agricultural lime into it or will the compost help raise the pH? Do I need to do the same for the blackberries and raspberries? Also since I seem to have high Mg, is there a way to make sure I don't get lime that has Mg in it. Will I be in danger of too much calcium if I add lime? For the blueberries, which like acidic soil, I was going to mix in compost and peat moss into the clay. I was reading that blueberries do well in pH soils between 4 and 5. If my soil is 5.2 and amended with compost and peat moss, can I call it a day and leave it. Or do I need to get a soil acidifier (like Espoma) in addition, just in case?

Howard County Maryland

1 Response

The Buffer pH is a way for the lab to make a lime recommendation. You should have received a liming recommendation from the lab to increase the pH for the asparagus, blackberries, and raspberries. For these crops, the pH should be in the range of 6.2 - 6.8. If the lab did not give you a lime recommendation, you could use agricultural lime to raise the pH. Add about 100 pounds per 1000 square feet. You can do this when you improve the soil and add the compost. Do not remove the clay. Add the compost on top of the soil and use a garden fork to open up the clay and incorporate the compost into the existing soil. Do this for the asparagus and the berries.
Blueberries - All you need to do is improve the soil by adding compost and peat moss. Blueberries grow well in a pH range of 4.3 - 5.3.