The 5-4-3-2-1 method is a planting formula for designing a bed: one focal plant, two large shrubs, three medium shrubs, four perennial groupings, and five groundcover or filler plants. Working from one to five forces a hierarchy, so the bed has a clear star instead of fifteen competing one-off plants.
Scaled to a typical 10 by 4 foot foundation bed, that might be one small ornamental tree, two viburnums, three dwarf hydrangeas, four clumps of catmint, and five sweeps of creeping phlox. Repeat the same formula in the next bed with the same plants and the yard starts reading as designed rather than collected.
It is a layout guide, not a law. If you want to check the proportions before buying, mock the bed up on a photo of your house with AI landscape design first.