Homegrown: Pruning raspberries

Lisa Slattery, Linn County Master Gardener, provided the following about pruning raspberries:  

March and early April are prime-time for pruning raspberries, but before you get started, you need to know what type of raspberries you have. There are several types of raspberries.

 For Summer-Bearing Red Raspberries you should remove all weak and damaged canes at ground level, leaving the most vigorous canes which are approximately 1/4 inch in diameter when measured 30 inches from the ground. Also remove the top 1/4 of the canes plus any winter injury. Cane-tip removal or “heading-back” prevents the canes from becoming top heavy and bending over under the weight of the crop. After the summer crop produces, prune off the old fruiting canes at ground level.

 Fall-bearing raspberries naturally produce two crops (sometimes referred to as the two crop system). The first crop is produced in late summer or early fall at the tips of the current season's growth. The following year, a summer crop is produced on the lower portions of these same canes. Prune for the two crop system the same as you would as it is described above for summer bearing raspberries.

For fall-bearing only red raspberries (one crop system), prune all canes back to ground level in March or early April. You won't get a summer crop, but the early fall crop should mature a few weeks earlier plus the crop yield should be larger using the one crop system versus the two crop system.

Red raspberries sucker from their roots, so maintain plants in a one- to two-foot-wide hedgerow and remove shoots that emerge outside this space with a tiller or hoe so you're not stuck with an unmanageable thicket.

For black and purple raspberries, prune out all the small, weak canes, leaving only four or five of the largest, most vigorous canes per plant. Trim the side branches to 12 inches in length for black raspberries and 18 inches for purple raspberries.

Some suggested summer-bearing red raspberries for Iowa include ‘Boyne,' ‘Latham,' and ‘Killarney.'  Fall bearing varieties include ‘Heritage,' ‘Redwing,' and ‘Autumn Bliss.' The best purple raspberry varieties are ‘Brandywine' and Royalty.' Black raspberries are not reliably hardy in northern Iowa. Gardeners in southern Iowa can choose from ‘Black Hawk,' ‘Bristol,' and ‘Jewel.' ‘Fall Gold' is an excellent fall-bearing yellow raspberry.

Pruned material should be removed and discarded to help control disease.