Oil in Soil

Iowa City, IA(Zone 5a)

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.

Anne Arundel,, MD(Zone 7b)

I'm sure it'll eventually degrade. Can you dig some dirt out dump it elsewhere and refill with clean dirt.? (oxymoron LOL)
Sunshine might help break down the grease or boost the bacteria needed.

Everett, WA(Zone 8a)

>> where they used to pour their kitchen grease.

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.

Iowa City, IA(Zone 5a)

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.

Everett, WA(Zone 8a)

>> There are grasses, wild carrot and for-goodness-sake catnip right up against it but nothing has moved in.

Man, that sounds really bad.

>> I can probably add the dirty dirt a scoop at a time to our compost bin in order to get it broken down.

I would be very cautious about spreading it around until you're SURE that it will indeed break down. It would be terrible to poison your whole compost heap!

Some persistent herbicides can last for many years in soil, even healthy living soil.

Maybe pick a spot you could afford to lose and make that spot 1/4 bad soil. Then see if you can get peas to sprout there. pea seedlings are supposed to be sensitive to many herbicides.

If not, see how many years it is before peas WILL grow there.

Maybe while waiting, you could excavate that spot several feet deep, and put the (presumably) contaminated soil into a heavy plastic bag, or double-bag it.

Or just dig one hole 3-4 feet deep, bury the bad soil at the bottom, and back-fill. Use the excess to backfill near your foundation.

Everett, WA(Zone 8a)

I hate to suggest this, since if it works, you might be stuck with some expensive regulatory-agency-mandated clean-up.

If you sent a soil sample to your state EPA that monitors chemical spills, and it was some herbicide, or motor oil, or heavy metals, or other toxin, they might identify it for you.

Of course, they would test first for things that are highly regulated and get places classified as toxic waste cleanup sites!

I searched on "RCRAinfo" and found this near you:

ZIP CODE: 52240


BRYAN JONES - phone 3193390500
FREDERICK J KULEVICH - phone 7082865310
KATHLEEN FLAHERTY - phone (847) 286-7199
MARGARET WHITNEY - phone 8472868616

Oh, I forgot. The House Republicans shut the government down. No EPA.

Iowa City, IA(Zone 5a)

EEP! and LOL!

I'm gonna trust that it's just pig fat.

Everett, WA(Zone 8a)

I hope so too.

But I really would experiment first with something less precious than compost. In my yard, at least, it's what I have the least of and need the most of.

I've started browsing the dumpster behind my local fruit stand every time I buy apples. I bring my own plastic bags for the apples, but I bring two extra for dumpster scavenging.

Then I chop big things with a cleaver on a piece of plywood, to help my compost pile digest the stems and twigs.

Anne Arundel,, MD(Zone 7b)

I doubt you can get it tested unless you're willing to pay. You could try the usual normal soil test and see if they report anything unusual.

Everett, WA(Zone 8a)

It occurred to me that the prior owner might NOT want to tell you if they broke a bottle of persistent herbicide right there.

Or dumped motor oil.

But living in NJ may have made me too cynical!

Dallas, TX

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.

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