Richard Jauron, extension horticulturist at Iowa State University, offers the following on spring pruning of berries and other small fruits:
Small fruits that are commonly grown in home gardens include raspberries, grapes, gooseberries, currants and blueberries. For maximum production, small fruit crops need to be pruned in late winter/early spring (March/early April). Proper pruning procedures for raspberries, grapes, gooseberries, currants and blueberries are outlined below.
The pruning procedures for raspberries are based on the growth and fruiting characteristics of the plants.
Summer-Bearing Red Raspberries
Remove all weak, diseased and damaged canes at ground level in March or early April. Leave the most vigorous canes, those approximately 1/4 inch in diameter when measured 30 inches from the ground. After thinning, remaining canes should be spaced about 6 inches apart.
Also, prune out the tips of the canes that have died due to winter injury. Cut back to live tissue. If the canes sustained little winter dieback, remove the top 1/4 of the canes. Cane-tip removal or “heading-back” prevents the canes from becoming top heavy and bending over under the weight of the crop.
Red raspberries sucker profusely from their roots. Plants should be maintained in a one- to two-foot-wide hedgerow using a rototiller or spade. Remove or destroy those shoots that emerge outside the one- to two-foot-wide hedgerow.
Fall-Bearing Red Raspberries (Two Crop System)
Follow the same pruning procedures as described for the summer-bearing red raspberries. This pruning option provides both a summer and fall crop.
Fall-Bearing Red Raspberries (One Crop System)
Prune all canes back to ground level in March or early April. While the plants won’t produce a summer crop, the late summer/early fall crop should mature one to two weeks earlier. Also, total crop yield is typically larger using the one-crop system versus the two-crop system.
Maintain the plants in a one- to two-foot-wide hedgerow.
Black and Purple Raspberries
Remove the small, weak canes, leaving only four or five of the largest, most vigorous canes per clump or plant. Cut back the lateral (side) branches to 12 inches in length for black raspberries and 18 inches for purple raspberries.
Grapevines produce fruit clusters on the previous season’s growth. Before pruning, a grapevine may have 200 to 300 buds capable of producing fruit. If the vine is not pruned, the number of grape clusters would be excessive and the grapevine would be unable to ripen the large crop or produce adequate vegetative growth.
To maximize crop yields, grapevines are trained to a specific system. The most common training system used by home gardeners is the four-cane Kniffin system. The four-cane Kniffin system is popular because of its simplicity. In the four-cane Kniffin system, the canes of the grapevine grow on two wires, one located three feet above the ground and the second six feet high.
If using the four-cane Kniffin system, select four canes on the upper wire, two going in each direction. Also, select four canes on the lower wire. To aid identification, some gardeners tie brightly colored ribbons or strips of cloth on those canes they wish to retain. All remaining one-year-old canes should be completely removed.
Going back to the upper wire, select two of the remaining four canes (one going in each direction). Prune these canes back to one or two buds. These short one or two bud canes are referred to as renewal spurs. The renewal spurs provide the shoots or canes that will produce next year’s crop. Prune the remaining two canes on the upper wire back to eight to 13 buds. The number of buds left on the fruiting canes is determined by plant vigor. If the grapevine is vigorous, leave 13 buds per cane. Leave only eight buds per cane if the grapevine possesses poor vigor.
Prune the four canes on the lower wire the same as those on the upper wire. When pruning is complete, no more than 60 buds should remain on the grapevine. When counting the number of buds on the grapevine, include both the buds on the fruiting canes and those on the renewal spurs.
Gooseberries and Currants
Gooseberries and currants produce the majority of their fruit on 2- and 3-year-old shoots. Shoots that are 4 years old and older produce very little fruit. After the first growing season, remove all but six to eight vigorous, healthy shoots. The following year, leave four or five 1-year-old shoots and three or four 2-year-old canes. After the third growing season, keep three or four shoots each of 1-, 2-, and 3-year-old growth. A properly pruned, established plant should consist of nine to 12 shoots. Pruning of mature plants consists of pruning out all 4-year-old shoots and thinning out some of the new growth.
Blueberry plants are shrubs like currants and gooseberries. Blueberry yields and fruit quality decline when blueberry shoots (stems) reach 5 years of age. In late winter/early spring, prune out any dead or diseased stems. Also, prune out stems that are 5 years old and older. Allow one to two new shoots to develop each year.
The pruning of small fruits really isn’t difficult. It requires a basic understanding of plant growth and pruning techniques, proper pruning equipment and (sometimes) a little bit of courage.