Tips To Prune For Big Blueberries
Last season, 2015, was a frustrating and disappointing season in our pick-your-own blueberry operation. We had a very heavy bloom and fruit set and could almost taste an anticipated record year. At the end of bloom, reality began to set in. When the final blossoms fell, we found few full leaves and almost no new growth beyond the first leaf. It was clear we had to do something to push new shoot and leaf growth which provide the nutrients needed to bring the berries up to size and to ripen them.
We ran irrigation nearly non-stop except for a short wet period during mid-summer and put on more nitrogen than usual up to harvest. The result was that we got average shoot and leaf growth by harvest time and were able to get a substantial number of berries up to an acceptable size for our pick-your-own customers.
In spite of our heroic efforts, a large number of berries remained quite small and did not ripen properly. We managed to salvage an average harvest but left more than half the total berries in the field.
Compared to the previous year, sales per customer were down. This observation is critical because it demonstrates that pick-your-own customers will not pick as much if the berries are small even though there are lots of berries.
This story began in 2014 when we had a relatively small fruit bud set going into spring bloom. We had exceptionally large berries and customers could not get enough; they filled their buckets and came back for more. We had excellent shoot growth and a heavy fruit bud set going into winter. We pruned normally, expecting a large crop in 2015 with the results described above. Looking at the two years, we actually had higher sales in 2014 than in 2015.
The Proper Number of Canes
As we got into pruning this past winter we began thinking about what we were doing wrong. First, we read Charlie O’Dell’s column in the February 2016 issue indicating the optimum number of canes should be about 8 to 10 while we had been keeping 15 or more.
Second, I found a package of 2014 ‘Bluecrop’ in the freezer to put on my cereal and noticed they were much larger than our 2015 berries. I counted these out and found it took 53 berries to fill a cup. These were apparently from our first picking.
Third, I recalled a conversation with my father, from many years ago, about pruning grapes where they counted and limiting nodes to avoid overproduction and maintain quality fruit.
How many fruit buds should we leave on a plant or on a cane during pruning in order to produce these large berries while still getting adequate return from each plant? My assumptions here are based on my northern highbush ‘Bluecrop’ planting on our poor clay mountain soils in north central West Virginia. I want a seasonal average of 60 berries per cup, and 12 pounds (two gallons) per plant. This calculation provides just 1,920 berries per plant.
Because fruit buds produce an average of 6 berries, we will need 320 fruit buds left on the plant after pruning. With 8 canes, we would need only 40 fruit buds per cane. Older, larger canes should have more while the new canes would have fewer. Obviously, we are not going to count fruit buds on each bush or even each cane. However, after counting a few canes, we should be able to make a reasonable assessment without counting as we go about pruning. Of course different climates, soils, and varieties will produce different results in this analysis.
None of this discussion has been verified by research, but it would make a nifty master’s thesis. I have pruned most of my fields with this idea in mind as well as Charlie O’Dell’s thoughts and observations from his column.
Our pick-your-own blueberry operations will prosper if we learn how to produce these large berries on a consistent basis. We may not get maximum pounds per plant, but we will get more of the crop picked, increasing our sales while reaping the invaluable benefit of gaining loyal customers.