Use this guide to divide clump forming plants such as herbs and perennials. Division is a form of vegetative propagation.
Divide and pot plants several weeks before you sell or plant them out in the garden to allow them to establish new roots. Dividing chives, coriander, mint, basil and parsley is great fundraising activity.
Choose good quality plants to divide and ensure they have lots of strong new growth
Take the plant out of the pot and with your hands roughly divide the plant in the middle.
Gently begin to pull the plant apart
Once you have two plants look to see if you can divide the plants further into quarters
Using the same technique you used before divide the plants again
Once you have divided the plant into as many pieces as you wish, pot up each plant separately
Water after potting and keep the plants in a warm light place until they have established
Look at this link for more details about propagation; click here