How Close Is Too Close for a Blueberry Plant?

CREDITS: Martin Zapien, Md Zohurul Kadir Roni, Gerardo H. Nunez

They say good fences make good neighbors, but plants do not have fences to prevent their neighbors from encroaching. That is why plant spacing is a critical consideration when starting a new planting. When blueberry bushes are planted too close together, plants compete for light, water, and nutrients. Competition aboveground makes plants tall and spindly. Competition belowground can cause nutrient deficiencies. Therefore, the right plant spacing can provide several benefits for farming operations. 

Planting density is the number of plants per unit area. A few years ago, most farms in Florida were using 2.5 feet by 9 feet spacing, resulting in 1,936 plants per acre. Nonetheless, to date, there is no consensus on the ideal number of plants per acre for commercial blueberry production. We have seen tighter (up to 2,250 plants per acre) and sparser spacing (as low as 1,750 plants per acre). The diversity of farm configurations nowadays stems from many factors including plant traits (like canopy size and growth habit) and logistics (like sprayer and mechanical harvester size). 

Modern blueberry cultivars come in a range of sizes and shapes. We have all seen the large, dense canopies of ‘Optimus’ and ‘Sentinel’ and the small, sparse canopies of ‘Chickadee’ and ‘Patrecia.’ We also know that plants like ‘Arcadia’ make globular canopies while plants like ‘Meadowlark’ make pillar-shaped canopies. A simple observation of how these varieties grow got us thinking that “one size fits all” is probably a bad idea for southern highbush blueberry. Therefore, last year, thanks to support from the Sustainable Agriculture Research and Education fund, we started a field experiment to evaluate optimal planting densities for blueberry varieties with distinct plant shapes. We planted ‘Optimus’ and ‘Meadowlark’ with in-row spacings of 18 in, 30 in, and 42 in. We have been collecting plant and fruit data since then.

Our first observations are encouraging. Compact varieties, like ‘Meadowlark,’ grew similarly regardless of planting density. In contrast, more vigorous varieties, like ‘Optimus,’ had reduced growth when spaced too closely together. Therefore, vigorous varieties might benefit from having more space to grow. Yields were not affected during the first year of evaluation, but they might be in the future. We expect plant to plant competition to increase as plants get larger and require more resources.

Machinery requirements are another major consideration when selecting plant spacing. Most farms already have turning headland to allow sprayers and mowers to make the U-turns necessary for proper operation. However, now that over-the-row (OTR) harvesters are becoming the norm, row spacing is changing. The current lineup of OTR harvesters from a leading manufacturer includes units up to 14.5 feet wide. So, many farms are adapting by spacing rows further apart. Something else to keep in mind is the OTR catch plates. We do not yet have data about how plant spacing affects the catch plates’ ability to close, but we plan to evaluate this in coming years.

Finding the right balance between planting density, yield, and production costs is essential for keeping operations sustainable and profitable. While plant spacing research might seem old-timey, we are eager to go back to the basis at a time when new cultivars and new farming tools are inviting us to rethink how close is too close. 

Picture 1.  Photo credit: Martin Zapien. Standard plant spacing in a blueberry farm.

Picture 2. Photo credit: Cecilia Heller. Over the row harvester in a blueberry farm.