Understanding how raspberry plants grow


By Robin Young | PREVIEW Columnist

Raspberries are a great, productive fruit plant that can be grown by gardeners in many parts of the United States, including all but the highest-elevation areas of Colorado. 

In addition to all of the delicious fruit they produce, they can also be an attractive visual element in the landscape. Unfortunately, backyard raspberry patches are often overgrown and unkempt looking. This is primarily due to the fact that most gardeners do not have a good understanding of how raspberry plants grow. This leads to improper pruning or even a total avoidance of pruning. Without proper pruning and management, raspberries will be less productive and more prone to diseases and pests. The goal of this article is to provide the understanding necessary for everyone to have beautiful, healthy, productive raspberries.

Raspberry plants are perennials. This means they come back year after year. But there is a catch — only the crown of the plant and its roots are truly perennial. The above-ground portions, known as canes, are actually biennial. This means that the canes have a lifespan of only two years. 

Their first year is spent growing vegetatively; the second year is spent flowering and fruiting. After they have produced a crop of fruit, they will die. In any given year, new canes grow from the crown of the plant, emerging sometime during April. These new canes will grow tall and leafy (and prickly), but they will not produce flowers or fruits. These first-year canes are known as “primocanes.” They will drop their leaves and go dormant during the fall and remain so until the following spring. After emerging from dormancy in their second year, these same canes are referred to as “floricanes.” At this point, these canes are not going to grow any taller. They will put all of their energy into flowering and fruiting on relatively short branches known as “fruiting laterals.” These fruiting laterals grow from the axillary buds that formed during the prior year at the base of each leaf. Once the resulting fruits have been harvested, it is time to cut the floricanes to the ground.

The growth habit described above is the norm for raspberries. Raspberries that grow in this fashion are known as “summer-bearing” or “floricane-bearing.” They produce crops of ripe berries during July. This is the way all raspberries grew until a major breeding breakthrough in the years after World War II. That was when breeders began working with wild plants that showed the ability to flower and fruit on primocanes (the first-year canes). 

These original wild plants produced small, seedy berries, but they did so from mid-August until a hard frost. Plant breeders recognized the season-extension potential of this trait and within a decade had succeeded in creating commercially viable, primocane-fruiting raspberries with great flavor. This primocane-bearing type of raspberry is also known as “fall-bearing” or “ever-bearing.” The vast majority of raspberries grown in Colorado gardens are primocane-bearing varieties. Primocane-bearing raspberries start each season by producing vegetative canes, just like floricane-bearing types. The big difference occurs in mid-summer. At that point, the primocanes of floricane-bearing types are still busy growing in a purely vegetative fashion. Primocane-bearing types, however, start producing fruiting laterals on their upper portions, leading to a late summer/fall crop of raspberries. The fruits produced typically start to ripen sometime in August (depending on variety) and continue producing fruit until a hard frost or freeze occurs.

There are two major advantages to growing fall-bearing (primocane-bearing) raspberries: easy pruning and no winter hardiness issues. Both of these advantages come from the fact that the primocanes grow and fruit in one season. Because you do not need to maintain any canes through the winter, pruning is as simple as mowing the whole patch to the ground. Similarly, since no canes need to overwinter, and because fruit buds develop in the same year as the fruit will develop, there is no chance for fruit buds to get damaged by cold during the winter. Considering the fickle winter weather we get in Colorado, as well as our frequent spring frosts, the fall-bearing varieties have been hugely popular in our state.

Before you decide you will only ever grow fall-bearing types, you should know that there are several varieties of summer-bearing raspberries that have adequate winter hardiness for our climate. By planting both summer- and fall-bearing varieties, you can greatly extend your raspberry season. 

If you want to get a little more advanced in your raspberry pruning, there is a way to get your “fall-bearing” raspberries to give you two crops per year (one in July, the other in August/September). Keep in mind that your primocanes only produce fruit along the upper portions of each cane. The remainder of the cane (the lower one-half to two-thirds of the cane) will behave like a summer-bearing type and produce flowers and fruit the following summer. So, after the plants have gone dormant in the fall, you will want to prune off only the upper portions of the primocanes. The following spring, the buds along the length of those shortened canes will start to grow and will produce fruit in July. Simultaneously, new primocanes will emerge from the soil. These will give you your fall crop. 

So, are you confused yet? Don’t lose hope. While this may seem very confusing now, there is an easy and fun way to understand it all: Observe your plants. Now that you know what kinds of structures and growth habits to look for, you will be amazed at how clear the distinctions are when you watch your raspberry plants grow for a 12-month cycle. You’ll be explaining the ins and outs of raspberry growth to your friends and neighbors in no time. 

For more information, check out “Raspberries For the Home Garden” by CSU Extension at: http:// www.ext.colostate.edu/pubs/garden/07001.html.

Volunteers needed

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