Knowledgebase
Elevated Phosphorous in Soil #749377
Asked May 11, 2021, 6:14 PM EDT
My husband and I have a large, deep planter box that we filled with bagged soil last year. Last year, we planted a number of seeds, which sprouted beautifully but then failed to grow further/thrive. I tested the soil with a home test kit, and it showed a surplus of phosphorous. So, we replaced most of the soil in the box, but when I tested again this year, the phosphorus level is still showing up as “surplus.” (Perhaps this is a problem with Alaska soil?) Are there any steps I can take short of replacing the soil (which is time consuming and expensive) that would help address this issue? Nitrogen and potassium levels are normal, and pH is a bit high (~7.5), but not crazy.
Anchorage County Alaska
Expert Response
Those home test kits are incredibly inaccurate. Surplus phosphorus is probably not your problem.
I recommend getting a soil test from Brookside Laboratory (blinc.com). You'll have to call them to get a quote and mailing instructions. You'll want test package S001AN.
When you get the results back send them to me at <personal data hidden>. I'll tell what the numbers mean and make a recommendation for improving the soil. I doubt you'll need to replace the soil.