Choose which class of blackberry bushes you wish to buy. Blackberry canes either grow erect, semi-trailing or trailing. Trailing plants need support, such as a trellis, in order to grow. Semi-trailing blackberries are thornless and also need support. Erect blackberry bushes do not require support, and some cultivators (varieties) are thornless. In general, erect growing blackberries can tolerate colder climates and are ready for harvest earlier than their trailing and semi-trailing counterparts.
Find out your USDA plant hardiness zone. Visit the US National Arboretum website to view a map of the different zones. Knowing which zone you live in will help you choose which cultivator to buy.
Select a cultivator within the class of blackberry bushes you chose. It must be rated hardy in your zone in order to survive the winters. Cultivators vary in fruit size, sweetness, tartness and time and length of harvest. In addition, some cultivators are less susceptible to disease and insects than others.
Figure out how many blackberry bushes you need. Each class of blackberry bush has its own spacing requirements. For example, trailing varieties are spaced about four feet apart, so for 100 feet of row, you will need about 26 plants (includes both ends).
Purchase your blackberry bush at a local, online or catalog nursery. A local nursery will be able to give you individual help in choosing the right bush for your situation, and you can pick out a healthy-looking bush. However, online and catalog nurseries will have more cultivators available and if you buy in large quantities, they may be a cheaper option. Look into their warranty policies, if any, especially for online and catalog nurseries where you don't get to personally select the bushes you are buying.