While raspberries and blackberries are not the same species, the growth and fruiting characteristics of blackberries are similar to raspberries. The blackberry plant's roots and crown are perennial, while its stems or canes are biennial. Blackberry canes are strictly vegetative during the first growing season. These first-year canes are referred to as primocanes. The following year, these same canes (now called floricanes) flower, produce fruit, and then die.
Types of Blackberries for Iowa
In Iowa, the canes of most blackberry varieties suffer extensive winter injury. As a result of this damage, plants produce little or no fruit.
Winter Hardy Summer-Bearing Varieties
There are two hardy varieties that can be successfully grown in the southern half of the state. 'Darrow' produces large fruit on vigorous, erect, thorny canes. 'Illini Hardy' bears medium-sized fruit. The fruit are produced on vigorous, erect, thorny canes.
Primocane-bearing blackberry varieties (Prime-Jim™ and Prime-Jan™) are a new option for gardeners in Iowa. Prime-Jim™ and Prime-Jan™ produce fruit in late summer/early fall on the current year's growth. Fruit are medium-sized, conical, soft, good flavored, and glossy black in color.
Pruning Summer-Bearing Blackberries
To obtain maximum yields, winter hardy summer-bearing blackberries, such as 'Darrow' and 'Illini Hardy', must be pruned properly.
In late winter or early spring, prune out canes that are diseased, damaged or crowded, leaving four to six healthy canes per plant. Also, prune back the lateral or side branches to a length of 12 to 15 inches to encourage larger fruit.
In summer, pinch out or cut off the tips of the new canes when they reach a height of 36 inches. Pinching encourages side branch growth and increases the fruiting surface area, resulting in higher yields. After the last harvest, cut off the old fruiting canes at the soil surface. Remove the pruned material from the garden and destroy it.
Pruning Primocane-Bearing Blackberries
Because of their different growth habit, pruning primocane-bearing blackberries, such as Prime-Jim™ and Prime-Jan™, looks a little different.
For these varieties simply prune all canes back to ground level in late winter or early spring. No additional pruning is necessary during the remainder of the year.