There is a tiny patch on the shaded east side of my house where no plant will sprout or take hold. I can't really tell a difference in texture from the surrounding soil, just a bare zone. When I had a chance to ask the previous owner about it, they mentioned that spot is where they used to pour their kitchen grease.
Is there a way to fix the oily soil? I suppose I could put an ornament there, but would rather try to remediate if possible.
Interesting problem! Since I'm used to dense, poorly aerated soil, my first idea would be to loosen up that soil to give microbes more air and perhaps a better chance to digest the grease. Dig in some bark shreds, coarse sand, shredded leaves, shredded paper.
Or even just turn it over or fork it up, if you're not already trying that.
>> I can't really tell a difference in texture from the surrounding soil, just a bare zone.
That kind of rules out "no aeration".
Does it stay wet longer than nearby soil, after a heavy rain? Grease might have clogged up the deep subsoil, slowing drainage, which would then kill roots each time it rained.
Hmm, maybe dig a sample and send it to a local soil-test lab. mention "nothing grows" so they test for herbicides.
Maybe after the prior owners got used to pouring grease there, someone decided that motor oil was a lot like kitchen grease! Motor oil would be bad and long-lasting.
One variation on completely replacing the soil is to dilute it with healthy soil. Seeding it with a little bit of other soils may introduce some bacteria that do know how to munch on grease.
Mixing a little of the contaminated soil into a part of your yard you care less about may stimulate the bacteria in that soil which can break it down, once it is diluted.
But that assumes you don't have some OTHER problem in that soil, like a really persistent herbicide.
Once I spread some sand that came from under someone's backyard pool in spots of my lawn. I'm pretty sure that sand had a persistent herbicide in it, because those spots died off and only came back after a few years of exposure to sun.
>> no plant will sprout or take hold.
Have you tried some extra-aggressive plants like grasses, clover, or local cover crops? Once one root ball manages to co-exist with it for a few months, I would expect soil microbes to go the rest of the way and break down kitchen grease.
It seems strange that simple grease would be slow to biodegrade in aerobic soil. It might not be very water-soluble, but grease breaks down into fatty acids which bacteria can certainly take up and break down.
if the soil is airy enough to have any bacteria, they should be breaking it down already.
If you were willing to experiment with options that would be bad for healthy soil, two possibilities come to mind. They are bad ideas unless the patch is so big that you're willing to risk soil around it, to rescue it.
Small amounts of detergent or soap might dissolve grease enough to make them more accessible to microbes.
Concentrated bases will break down grease or fats into fatty acids and glycerol, both soluble and digestible. But then you have a spot of very basic soil! I'm talking about small amounts of hydrated lime or quicklime. Again: this is likely to kill plants until it is diluted by rain or countered with something acid like vinegar or ag sulfur.
RickCorey, thanks for the great suggestions. The patch may hold moisture slightly longer than adjacent areas. It's hard to tell. We have had two very drought-condition summers in a row.
Before I knew about "the spot," I killed some lovely little woodland shade starts. Next I tried sowing foxgloves there but they did not sprout. There are grasses, wild carrot and for-goodness-sake catnip right up against it but nothing has moved in.
It's a small enough area that I should be able to get most of it up and replace it with fresh soil. It's a half circle about 12" in diameter, right up against the foundation, I don't know how to guesstimate the depth.
I can probably add the dirty dirt a scoop at a time to our compost bin in order to get it broken down.
I have no clue, at least right now, about a remedy. But I would NOT add any of that soil to your compost. Or spread it around. RickCorey is right in saying that the prior owner could have dumped anything there. Or maybe had an old car battery or engine sitting there for years, just leaking away.