Latest revision on K-CUP recycling for seed starting -- reviewing and learning from previous experiments, this is my latest/improved method for repurposing them for seed starting.
1-3/4' diameter after cutting off the rim is a very good size for starting tiny seeds up to tomato/pepper seed size. 7 of them fit snugly in the larger takeout sandwich and pastry clamshells, optimizing space.
One disadvantage is that it lacks sufficient depth when the seedlings are ready to start growing true leaves, and I always want to plant tomato seedlings deeper when uppotting.
Last year, I started experimenting with double-deckering them after they outgrew the cup. This year, I've hit upon a way to make this process easier. Also decided the filter creates more problem than it's worth, and easiest way to get them out is to simply cut the top rim off along with the attached lid, then trim the top edge another sliver to cut off the glued edge of the filter along with the plastic. Then the filter and UCG dump out easily.
Because the inner cup has no bottom, they Can be popped out easily for dividing and uppotting as necessary. For simply double-deckering, I just pull the inner cup out, fill the bottom cup, and stack. A tape on each side has turned out to be essential to keep the upper cup from falling off until the roots fill the bottom cup. At planting time, I simply cut off the bottom and sometimes cut up the sides to use as plant label (a little nail hole and twist tie).
It turned out that I can fit 14 2Kc's in tripled clear plastic egg carton lid. Only problem is they have to be matching cartons. I hope I can find more among the saved egg cartons.
I think the larger clear container is the one from H-mart (Korean super market) I can't remember how many, but the 2Kc's also fit exactly.
The white one looks like a 1/2 dozen egg carton, but is actually a tray in which Mochi Icecream came in, and it wastes space due to the spacing between the cells, but I can make it work by putting two more on the ledge between the cells for total of 8. It's sturdy and can also be strengthened by stacking two trays.