curious to know how far down you dug?

I don't know that anyone has asked that before. Generally grasses would rot away in a few weeks, especially if the soil was wet and covered. With some of the more pesky plants used to spreading via underground runners (rhizomes), it might take longer.

What you might do is dampen the soil, add a bunch of fresh horse manure, and mix it together. The manure will bring up the temperature of the pile and essentially compost it for you. The heat from the composting process will literally cook the zoysia plants and kill them. The end result of the composting process is a very sweet smelling material...believe it or not. If you uncover it and it still stinks, the composting is not over. This time of year you might have access to a lot of dry leaves. You can cover the pile with those dry leaves and they will absorb the ammonia gas, and smell, from the manure. This magical process was discovered by the Russians back in the late 1800s and apparently never translated into the Western culture...until now.

My depth varied between one and three inches. This was not a strong well-established turf that I was digging up. It was just some spots of Zoysia here and there that had sprung up randomly.

Wow, DCHall, your posts are gems! I always read your posts several times.

It has actually been 2-4 years since I stuck this dirt in the corner. I've lost track of the time. It sounds from your post like several years is plenty of time for the roots to die off.

Just a guess, but you'll know if they're dead or not by the lack of new growth. The roots should need some leaves on them for photosynthesis? to continue to grow. At least that's how the Zoysia in our garden seems to work. I can pull up a 1' long stolen/root, 6" deep but it always has at least leaf or two attached on the surface.

Spray the pile of dirt with roundup. the longer you can wait the better. I did the same and just threw it away instead of risking zoysia re-infestation.