Blueberry pruning both art and science
Question: We have blueberry bushes that are approximately 40+ years old that began to slow production. In the fall of 2016 we cut them to the ground, and now we have many shoots about 4 feet tall. What do we do next spring?
Answer: Blueberry pruning is as much art as it is science. As you've discovered, pruning is closely tied to crop production and pruning too aggressively (or not aggressively enough) can impact your blueberry's future production.
The best way to prune old blueberry bushes such as yours is to perform a careful renewal pruning where new cane production is encouraged by cutting half of the oldest, thickest canes back severely to the ground. This forces new canes to grow from the ground. Over the course of the following two to three years, remove the remainder of the oldest, thickest canes a few at a time until only newly produced canes remain. This allows the plant to continue producing a moderate crop while the bush is being slowly rejuvenated. Cutting back all the canes at once, as you did, encourages rapid new cane production which can, unfortunately, influence crop production for several years.
Blueberries produce their flowers on old wood, meaning that the buds for each year's berry crop are formed during the summer and autumn of the previous season. Your heavily pruned bushes may take a few years to develop flower buds because the plants have had to put a great amount of energy into pushing out all new growth to replace the old.
I suggest you thin out those young, new canes by pruning all but the strongest five to six canes per bush down to the ground. The remaining canes should be allowed to grow, but they may take two or three years to develop flower buds.
When spring arrives, fertilize your blueberry bushes with an acid-specific organic granular fertilizer, such as HollyTone, according to label instructions and mulch them with 1 to 2 inches of pine straw, shredded hardwood bark, or shredded leaves. Do not over-mulch as blueberries have shallow, fibrous root systems that resent thick layers of mulch. And do not apply a fertilizer that's high in nitrogen as this will encourage even more shoot growth.
Future pruning should take place every spring, or every other spring, typically in mid to late March. Each year, remove one or two of the oldest, thickest canes from each plant by cutting them down to the ground. New canes will develop every year to replace the old, removed canes. This encourages excellent blueberry production every year and keeps the plant from getting “tired” as it ages.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control” and “Good Bug, Bad Bug.” Her website is jessicawalliser.com.
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