Ok to layer dirt in my compost?

May 29, 2016 4:37 PM

I have equal parts dirt and 2/3rds complete compost. Can I combine?

I have a large amount of dirt/sod from removing grass while preparing a large bed. It is in a big pile in my yard, and feels more like silty top soil than sod. I also have a large compost pile (leaf mold and kitchen scraps, cold compost with a year into it). I have a little more dirt than compost.

Last, I recently made a large compost bin with two 48" cube compartments. My plan is to move all this stuff into the bin and get my yard looking better.

At this point, should I keep the dirt separate from the compost, or can I combine? The dirt seems pretty dead, microbe-wise and I worry it will retard the ongoing compost process. The long term plan is to use in a raised bed garden.

Thanks for the advice!

posted by cgs to Home & Garden (6 answers total)

You can, but your intuition is correct that it will slow the composting of older compost. If you aren't in a rush, you can mix the sod in as you go with new compost.

Alternately, just cover the sod pile with some plastic and let is compost on its own slowly. You can also bury the sod underground a couple feet (or at ground level in the bottom of your raised beds) and it will eventually rot away. Plant roots won't have much trouble pushing through the sod if they need too.

If you need the soil right away, you can make a screen with some mesh and 2x4s and separate the roots from the soil (and compost the roots).

I've used all these methods. Just leaving it in a pile under a tarp is the easiest by far and seems to take a couple years.
posted by ssg at 4:51 PM on May 29, 2016

Best answer: I would use one of those 4' cubes you made. Put in all of the compost, then put the dirt on top. In a year, then mix them together for the new raised bed you're planning. Don't intermix them now, that will slow the completion of the compost.
posted by yesster at 5:01 PM on May 29, 2016

This USDA publication on composting explicitly says to use layers of soil in between composting materials, though not in equal parts.
posted by XMLicious at 5:09 PM on May 29, 2016 [1 favorite]

I've always added layers of earth (aka dirt, but that always sounds pejorative to my Brit ears) to my compost piles. I think it improves the compost by adding minerals, but never thought about it slowing the composting process.
posted by anadem at 6:05 PM on May 29, 2016 [1 favorite]

I can't tell where you are located which really determines your compost speed - colder climate = slower composting.

In the future keep the leaf mold out of the compost. It seriously retards compost breakdown. It can break down on its own in large garbage bags with a few holes in them to let moisture and rain in. It makes an excellent top dressing in a year or so.

I'd just mix the dirt in and give it a really good aerating stir every week. You can also accelerate the process by adding 'compost activator' (your pee!). If it gets stinky and slimy like a swamp back off on the compost activator and lawn clippings as you have too much nitrogen (this could be a good point to add dirt in). It's important to have enough but not too much moisture throughout compost. Too dry and nothing happens. Too wet and things get anaerobic and gross. Air is also important hence the need for stirring. Both moisture and stirring also discourage rodents taking up residence.

Also throw in any worms, snails or slugs you find in your garden.
posted by srboisvert at 6:13 PM on May 29, 2016

I'd make a pile of the dirt next to the compost bin and just add a little dirt evety once in awhile to the compost you are making in the bin. In my experience, a bit of dirt (no more than a third of the entire pile) speeds up the compost process.
posted by WalkerWestridge at 10:16 PM on May 29, 2016