Highbush Blueberry Post Harvest Nutrition

Another blueberry harvest is finished, and now it is time to relax and put your feet up. Or Is it? Proper post-harvest plant care can set you up for a great return next year and vice versa is equally true. Abandoning the field now is not the best way to proceed.

Immediately following harvest is when highbush blueberry plants start to set the buds for next year’s growth and flowers. This is one of the most important times in the plants growth cycle in terms of determining your production for next year. The plant is starting to store nutrients and sugars for next year’s early season growth. Maximizing the number and nutritional content of these floral buds now is one of the best ways to ensure that your production for next year reaches its full potential. Two very important nutrients to apply at this time are Boron and Zinc.

Boron has many functions within the plant, including strengthening cell walls, cell division, sugar transport, and fruit and seed development. It is the last item here that we are most concerned about at this time. It has been well documented that boron is essential for proper pollen tube development as well as the germination of the pollen itself. Making sure that the pollen has enough boron is essential for maximizing your harvest. Now, all of this action of germinating pollen and pollen tube development happens in the spring. So why is it important to spray boron during the summer/fall? Studies have shown that fall applied boron is able to be stored by the plants for use in the springtime while the flowers are open and pollination is happening. Increased yield has been demonstrated in highbush blueberries with fall applied boron. Boron deficient plants can also have a reduced number of floral and leaf buds developing in the summer/fall.

Zinc also has various functions within the plant. These include internode elongation as well as a role in production of key growth hormones and enzymes. Zinc also plays a role in the development of the fruit seeds. Therefore, it stands to reason the time of greatest demand for zinc would be in the early spring while the plants are undergoing aggressive growth. This has been demonstrated to be true by Oregon researchers. It has also been shown that the availability of zinc in the soil is greatly related to the soil temperature. Cold soils will inhibit the uptake of zinc by the plant. Since early spring is the time of highest plant demand, and also the time when it is hardest for the plant to take it up, it makes sense to foliar apply zinc at that time. While this is very true, however in the Fraser Valley many of the fields are inaccessible to spray equipment due to wet soil. The next best alternative is to do a fall/late summer application and let the plant store the zinc in the tissue to be used in the early spring.

If you happen to be applying granular fertilizer this fall, make sure to ask for boron and zinc to be in it. Usually our fall blends do. More common is to apply foliar fertilizer. While there are leaves that have not yet started to senesce, they will absorb foliar micronutrients, generally well into September. Choose from these foliar products to supply boron and zinc to your blueberry plants: