Hold off on pruning raspberries, blackberries

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By Jeneen Wiche

The bramble patch is usually cleaned up by now but the cold winter has set us back with a few of our garden chores.  But it turns out that this may be a good thing after all. The University of Kentucky has sent out a “blackberry alert” urging gardeners to hold off on pruning blackberry and raspberry until new shoots begin to emerge.  They are expecting more than usual die back due to our cold winter season.

Most brambles are biennial which means they fruit on second-year growth.  Blackberries are easy to deal with, just remove the arching canes that fruited last year and trim up and trellis the remaining new growth from last summer after you see the cane push new growth.  These canes will bear this summer’s fruit and these are the canes that we might see some damage on according to the University of Kentucky. 

Biennial raspberries are trickier. 

Most black and purple raspberry varieties are biennial so they flower and produce fruit on developing canes that are in their second year of growth. To maintain biennial raspberries your pruning technique will vary a bit from that used on blackberries and other ever-bearing varieties of raspberries, but I’ll get to that shortly.

During the first year, the canes that are not producing fruit should have the tips pruned out when they reach about three feet in height.  These canes will produce fruit the following year and by pruning the tips more lateral, fruit bearing shoots will form along the cane.  Canes without lateral shoots can be cut to about 2 1/2 feet to encourage more branching. 

In the second year of a biennial raspberry’s life, after the fruit is harvested, the 2-year-old cane will die back.  Go ahead and prune these canes to ground level after harvest is complete.  At the end of the summer thin the remaining canes, saving about five of the healthiest per plant.  Prune the lateral shoots of these canes to about 8-10 inches in length.

Red raspberries are treated a little differently: red raspberries are ever bearing and produce two crops of fruit in a year, one in mid-summer and a second in fall. Red ever-bearing raspberries typically have erect-growing canes that help to distinguish them from the black and purple cousins which have arching canes.  Most people grow the ever-bearing types.

To maintain two crops from an ever-bearing raspberry you want to remove the spent canes from the early summer harvest after the harvest is complete.  This allows all of the plant’s energy to focus on producing the second round of growth and fruit for the fall.  In fall, after the second harvest, thin the remaining canes that fruited, leaving about five of the healthiest canes for the next season. 

Some growers sacrifice the summer harvest of red raspberries so they will have a bumper crop in the fall.  If you choose to go this route you only need to prune once.  Cut (or mow) the entire plant down to ground now.  We take this approach because it helps to control the spread of disease.

Brambles are rather susceptible to fungal and viral diseases, so proper pruning is important.  It keeps the plants productive, yes, but it also allows for better air circulation and light penetration, and it removes diseased canes on a regular basis.  This is why we grow ever-bearing varieties and cut them all down in the fall of the year.  We don’t have an early crop of berries but we have less disease pressure.