Blackberries are perennial plants which typically bear biennial stems (“canes”) from the perennial root system.
In its first year, a new stem grows vigorously to its full length of 3-6 m, arching or trailing along the ground and bearing large palmately compound leaves with five or seven leaflets; it does not produce any flowers. In its second year, the stem does not grow longer, but the flower buds break to produce flowering laterals, which bear smaller leaves with three or five leaflets. First and second-year shoots are usually spiny with numerous short curved very sharp thorns (thornless cultivars have been developed purposefully).
Unmanaged mature plants form a tangle of dense arching stems, the branches rooting from the node tip when they reach the ground. Vigorous and growing rapidly in woods, scrub, hillsides and hedgerows, blackberry shrubs tolerate poor soils, readily colonizing wasteland, ditches and vacant lots.