Here are the steps to follow when dividing your perennials:
1. When possible, plan to divide your perennials on an overcast day with showers in the forecast. This will greatly help the plant recover from the roots being damaged. It would also be helpful to thoroughly water the plants a day prior to dividing.
2. When dividing in the spring, wait until new shoots are about 1” tall. If dividing plants in the fall, prune plants back to just a few inches tall.
3. Using a spade or garden fork, dig into the soil about 4”-6” beyond where the shoots emerge. Dig all around the clump then pry up on rootball. Do not try and cut through the roots while the plant is still in the ground. When you do it this way, you have no way of knowing how many roots you will be getting and could be wasting parts of the plant.
4. Lift out the entire clump as completely as possible and sit it on top of the ground or on a tarp.
5. Using a sharp spade or knife, gently cut through the roots, dividing the clump into as many pieces as desired. Each division should have at least 3-5 vigorous shoots and a healthy supply of roots. If the centre of the plant has died out, divide the living, outer portions into smaller clumps and throw out the dead, centre portion.
6. Enrich the soil in the new planting areas with compost, composted manure, or triple mix before planting new divisions. Fertilize new plantings by scattering a handful of bone meal in the bottom of the planting hole. Bone meal is high in phosphorus which will help stimulate root growth.
7. Fill in around the plant roots with triple mix or compost. Make sure that the plant is in the soil at the same depth that it was previously and water well.