Fill the containers in a seed flat with 1 inch of soil each. Place buttercup seeds on top of each flat compartment about 1 inch from each other, then cover the seeds with about 2 inches of soil. Place the flat in a plastic bag and leave it in your refrigerator for three weeks.
Dig holes in shady areas of your yard that are about 3 inches deep and will fit the flats comfortably. Remove the flats from your refrigerator and take the plastic bag off, then tap the bottom of each flat compartment to help loosen the flats for removal. Cover each hole with a plastic or glass cover. Germination time can take anywhere from two weeks to three months.
Move seedlings to their final desired location, which can be one or more sections of your yard depending on preference. Space the seedlings at least 2 inches and as much as 24 inches apart.