Overcrowded, poor flowering and floppy perennials can be invigorated with a shovel and a bit of your time and energy.
Dig and divide perennials to improve their overall appearance and create new plants to use or share. The best time to divide spring bloomers is in fall, fall bloomers in spring and summer blooming perennials in either spring or fall. But most gardeners have found the best time to divide is when you have the time.
Use a sharp spade to dig up the clump. I like to lift the clump out of the soil and use a linoleum knife to cut the plant into smaller sections. Discard and compost the dead center. Divide into four, six or eight pieces.
Prepare the soil for replanting by adding compost or organic matter. Plant and water to get your new plants off to a good start.
A bit more information: Try this trick when dividing large, hard to manage perennials. Use a sharp spade (shovel) and dig around the outer edge of the plant to be divided. Then use the spade to slice through the root ball dividing the plant into four or eight sections. Now use the shovel to wedge the smaller pieces out of the ground. You can also dig small sections from the outer edge of the plant. This is a good option when the perennial is performing nicely and you just need a division to share or fill in a void in another part of the yard.