I have several established North Alabama Clay flower beds on top of which I’ve put 1-2-3 inches of compost. I’ve planted Sugar Snap Peas, using potting soil to fill the seed depressions that I made using a hoe handle.
The beds are too small to operate a garden tiller in. I was in a hurry, expecting rain. And I decided it would be too tough to try to hand dig the compost into the clay. And perhaps I was lazy! So I just applied the compost, then planted in it.
Now I read that putting compost over clay can be a Big Mistake. That moisture will pass right thru the compost and pool on top the clay.
One idea I have is to get a really long 1/4 inch drill bit and use a portable electric drill to drill thru the compost, down into the clay to possibly make hundreds (thousands?) of drain holes in the clay, and possibly some of the compost will fall down into these holes. But as I said, the Sugar Snap peas are already planted there. The potting soil, once watered, looks just like the compost. So till things sprout, I cannot tell where the Sugar Snap peas are, and I hate to risk destroying them.
I also have a larger, about 2.5 inch diameter, bulb planting auger bit that I might use. But my portable battery-operated electric drill seems unlikely to be powerful enough to auger 2.5 diameter holes thru clay, not to mention thru the Maple Tree roots! In my compost tumbler, it works well. But my clay is more like concrete, whether wet or dry.
I never got any suggestions.
My Sugar Snap Peas sprouted so sporadically that I ended up replanting them several times. Watching and waiting for them to sprout, I missed any early opportunity to auger up the soil in these beds.
I suppose since the Pea plants are so minimal, and the cool weather is just about past, I may as well plant my green beans between the peas and go from there.
You could move the plants into pots, till in the compost, and then replant them.
You could try tilling in some gypsum with the compost to loosen the soil.
Or you could just put in raised beds with about 8" of topsoil..
Or grow plants that like/tolerate clay soil
I’m still making compost in my ComposT-Twin tumbler to use somehow, some where. The peas never amounted to anything in the circular bed pictured. I planted onion sets there. They never amounted to anything. I planted corn in there. It sprouted and mostly just sat there till my wife pulled it up, thinking it was grass.
So this particular bed and the one in the background with the bird bath has been basically a time and work sink and a total loss this year veggie-wise. Then rabbits and who knows what other critters came and overnight ate all my green beans that I planted in several of my gardens. I had one pole bean growing up one trellis. But when I noticed it dead, the lowest 6 inches of the stem was simply gone. Somebody ate the stem, killing the entire pole bean.
So now I’m exploring rabbit fence as well as what to do about my clay soil and the prolific tree roots!