Growing fresh blackberries around your home is one of the easiest ways to get free berries for very little effort. As blackberries grow, year after year, new shoots are sent up to grow and make leaves. The following year, the previously leafy canes will bear fruit. After a cane bears fruit it is no longer needed for the production or health of the plant and it can be removed. To prune blackberry plants you'll need to keep an eye on the growing canes so you know which ones are new, productive or old.
Look over your blackberry plant in late spring or early summer. There will be three main types of canes showing: first year leafy canes with green stems, second year fruiting canes with woody stems and flowers or fruit and old woody canes with no flowers or fruit and sometimes no leaves.
Clip away only the old canes (3 years old or more) by cutting them back to within an inch from the ground. These canes will be brown throughout with no green even on the inside of the cane. Cut out all of the old, unproductive canes.
Harvest your blackberries as they ripen and pull away from the plant with ease. Frequently harvesting every three to five days should allow you to catch the berries at the right time. Harvest until all of the berries have ripened and been collected.
Clip away the fruiting canes of this year to within an inch from the ground after the entire harvest is over. All of these canes can be removed after harvest since they will not fruit again.
Prune the blackberries in subsequent years by cutting back the second-year canes (last year's green canes) after harvest to continue the cycle of only allowing productive canes to grow. If your blackberry plant has more than five new leafy canes growing you can choose to cut back the excess canes to the ground as well.