If you're starting a container planting from scratch, Roger recommends covering drain holes with a piece of a broken terra-cotta pot, then adding a little gravel and some landscape fabric to ensure good drainage before you fill in with potting soil. In milder climates or where the plants will be left in pots year-round, mix in some aged compost before you plant, then top with mulch to keep soil moist.
Because Roger usually replaces wintertime displays with colorful annuals in the spring, he doesn't add any soil amendments in the fall or even worry about loosening up the soil more than needed to fit in the roots. He also doesn't bother to loosen tangled root balls because the plants won't do any growing over the winter. As he says, "They're just going to sit there and look pretty." He is careful, however, to leave enough space above the soil line for 3 or 4 inches of mulch (he likes aged pine bark). Thick mulch insulates the roots and protects them from drying out if they are popped out of the soil during a hard freeze.