No Longer Considered Impractical, the Practice Signals a Future of Possibility
Grafting is a technique that combines a plant with desirable fruit attributes (like a modern southern highbush blueberry variety) with another plant with desirable root attributes (like sparkleberry). Researchers at the University of Florida started grafting blueberry scions onto sparkleberry rootstocks more than 15 years ago. More recently, the Southern SARE and the Florida Department of Agriculture and Consumer Services have funded new rounds of research for this unique blueberry farming system. In this article, we present some of our recent findings.
Why do we use sparkleberry?
Sparkleberry is a plant in the same genus as the cultivated blueberry. However, unlike blueberry plants, sparkleberries are adapted to upland mineral soils and develop deep root systems that can access moisture from deeper soil layers. Recent research in our lab has allowed us to test how grafted blueberry plants respond to drought. When we withheld irrigation for 9 days, blueberry plants growing in their own roots were stressed. They closed their stomata (limiting photosynthesis) and lost their leaves. In contrast, grafted blueberry plants took up water from deep soil layers, avoiding drought stress. This allowed grafted plants to keep their stomata open and keep photosynthesizing under these adverse conditions. We believe this is one of the reasons why mature grafted plants can outyield own-rooted plants.
Finding that deep roots can affect the water status of grafted plants has us thinking of other possible benefits. This summer, we will be testing the effects of deep root systems on uptake of mobile nutrients (phosphates and nitrates). If deep roots can take up these nutrients efficiently, grafting might be a way to reduce fertilizer use in blueberry farms.
What is the best method to graft blueberries?
As we learn more about the benefits of grafting blueberry into sparkleberry rootstocks, we are commonly faced with a question: How should we graft blueberries? The answer is not simple. Sparkleberry plants are difficult to propagate and graft, which can make grafted liners costly. Thus, we have been investigating the best timing and method for grafting. Our recent research pointed out that grafting in the spring leads to noticeably faster plant development compared to fall. Also, scions grafted close to the crown developed more rapidly than scions grafted further away. Currently, we graft 12 to 15 inches away from the crown because we want to produce a plant that resembles a small tree. We believe that the plant architecture of a small tree could be ideal to minimize fruit losses during mechanical harvest.
After trying several other techniques, we have settled on using side grafts to produce grafted blueberry liners. The most desirable scion is a small blueberry branch (1 to 2 inches) with several nodes. A desirable rootstock is one that has a straight trunk that is at least as thick as a pencil. We recently published an instructional video that walks you step-by-step through the grafting process. The video can be found at https://youtu.be/B78G8Bfd1Fo?si=mMLswEflXAB_SXaL, on the UF/IFAS YouTube channel under “The Feasibility of Grafting Blueberry Plants,” or by scanning the following QR code:
The Future Is Bright
We are very happy with our recent results, but we are buzzing about the future. Last fall, we planted grafted blueberry trials in commercial farms in Archer, Fla., and Alma, Ga. There has not been a commercial trial of grafted blueberries in over a decade! Something unique about these plantings is that we put all the grafted plants in large blocks. This will allow us to run an over-the-row harvester on these plants when they reach maturity. Water and fertilizer savings are great prospects, but we know the industry needs solutions for mechanization. We look forward to learning how grafted plants respond to mechanical harvest in future years. Grafting is one of several applications that can help us reduce harvest costs.
Although grafting blueberries once appeared impractical, our recent research has revealed its benefits and demonstrated effective methods for producing grafted plants. We are excited to continue developing a commercial solution to introduce grafted blueberry plants to farms in our state.
Picture 1. Young grafted blueberry planted in pine bark beds.
Picture 2. Grafted blueberry field planted in unamended soil.
CREDITS:
GERARDO H. NUNEZ, JEFF WILLIAMSON, VALENTINA GOLES VARELA, and CECILIA RUBERT HELLER
