statrting new plants by separation is easiest if the mother plant is growing in a pot or bag, but it sounds like your bamboo is already growing in the ground. This requires a little more careful digging, but you can do it. your plant should have plenty of culms at four years. first wet the plant and all the leaves and try to do the separation in the shade if possible to prevent your plant from drying. carefully dig around the bamboo where you want to remove small section. be careful not to damage the rhizome when digging. sometimes water is helpful to rinse and expose the rhizome. be sure each section you remove has a least 2 healthy culms. make a vertical cut through the rhizome neck near where the rhizome joins the mother plant. remove the culms and rhizome with roots attached. repot each separated plant in potting mix and flood each with water. move the pots to a shady, high humidity, warm area and flood with water for 2 or 3 days. When the plants have recovered and are showing strong growth you may plant them back in your screen. Be careful not to stress the mother plant too much and remember that the transplants may not survive, but you have a much better chance of success if you are careful not to damage the rhizomes. For large bamboo this technique of seperation may be to difficult. check the next 2 topics for more information on propagation from culm cuttings and branch cuttings.