Wild bramble fruits such as raspberries and blackberries protect their canes with rows of sharp thorns. Domestic types of brambles developed for larger fruit and greater plant vigor usually do grow thorny canes, but some cultivars of raspberries and blackberries offer thornless harvests as well as improved flavorful berries. Other raspberry varieties present fragile spines rather than large thorns, and still others grow fewer thorns than found on wild plants.
More than 200 species of raspberries exist. The five colors of today's domestic varieties descended from Rubus ideaus, or the wild red raspberry, and Rubus occidentalis, the wild black raspberry. Crosses between these two thorny plants yielded raspberry hybrids and mutants with fruit colors including red, black, yellow, orange and purple. All raspberry plants grow with perennial root systems but biennial canes. Most raspberries fruit once on flourocanes 2 years old, but everbearing types may fruit twice in a season. Everbearing raspberries flower at the tips of first-year canes called primocanes, as well as farther down on the canes in their second year. The canes of all types die after fruiting in the second season.
Size and vigor of raspberries vary considerably with variety. The presence of thorns does not necessarily mark plants with better disease resistance or higher productivity. Vigorous varieties may bear abundant thorns or only a few, or bristle with smaller spines that usually break off when touched. Color of fruit indicates the cold hardiness of the plant, with red raspberries showing the most cold tolerance. Purple and black varieties survive temperatures only down to 5 degrees Fahrenheit. Yellow raspberries exhibit characteristics similar to red raspberries.
Raspberry varieties that grow canes with spines rather than thorns present fewer problems when pruning or harvesting. Killarney and Boyne red raspberries grow shorter canes than many thorny varieties and show good cold hardiness. Both yield medium-sized flavorful fruit. August Red and Fall Red raspberries also grow short spiny canes. These everbearing varieties yield softer fruit. August Red ripens earlier than other everbearing types, but Fall Red requires a longer growing season.
One completely thornless raspberry, Thornless Canby, grows slender canes that may reach 6 feet and require trellising for support. Thornless Canby yields bright red large berries. The firm fruit has good flavor. These vigorous red raspberries need good drainage and plenty of growing room. Plants need a spacing in the row of six feet and 12 feet between rows. Trellises with multiple wires placed on supports 3 feet high allow grouping first-year canes in the center of the row while fruiting canes bend outward for easy harvest.