You can plant pampass grass into the landscape anytime the ground is not frozen or during a summer drought. Spring or fall are both good times. Early spring before  you see the first signs of new growth is a good time to prune back most ornamental grasses. You don't want to wait until you see green shoots because then it will be difficult to remove the old brown stalks without cutting into the new growth. Late February or early March is when forsythia blooms in many parts of the country and this bright yellow shrub flowering in very early spring is always my reminder to prune back the Pampas grass as well as other ornamental grasses that have gone brown and dormant over the winter. Keep growing, Marianne Binetti