Raspberry plants need to be controlled through pruning to prevent their spread. Digging up unwanted raspberry plants is necessary to maintain good fruit production. Red and yellow raspberries produce numerous new canes from the base of the floricanes and from buds produced on the roots. The plants can spread in any direction. Black and purple raspberry cultivars do not send up sucker shoots from underground roots.
Raspberry canes have perennial roots and crowns but their canes live for two summers. The first year's green cane is called a primocane. After the first dormant period this cane develops a brown bark and is called a floricane. The floricane produces raspberries and then dies. It is the floricanes that can reach 15 to 20 feet in length and regrow into a new area. Digging them up is necessary to prevent the raspberry patch from spreading.
Digging up raspberry canes as soon as they appear prevents unwanted spread. Raspberries are very vigorous growers, able to reach 10 to 15 feet within a season. Raspberries spread by underground roots or canes bending over and starting in new soil. Plants take two years to grow berries but remain productive for several years once established.
Roots grow quickly from the parent raspberry plant to establish a new crown several feet away. Raspberry canes can be removed easily when the new shoots are 1 to 5 inches tall. Simply dig with a shovel into the ground beneath the growing shoot. Summer raspberries are pruned in the spring and after harvest and this is a good time to remove unwanted new plants.
Regular and thorough pruning can prevent additional unwanted plants from getting started. Pruning keeps new cane development under control and helps the plant's energy go toward fruit production. In spring pruning, all weak canes are removed, and tall canes are cut back to 4 or 5 feet. After harvest the fruit producing vines are cut back to 8 to 10 inches.
Problems with unwanted raspberry canes can be prevented by proper planting techniques. Plants grown on trellis systems and wire supports are easier to prune. Pruning keeps unwanted canes from spreading and creating new growth. The narrow hedgerow system is the favored planting system for raspberries. New canes are placed in rows 6 feet apart with 2 to 3 feet between the plants. Allow new primocanes to spread along the row but not wider than 12 inches.