One of the new approaches Florida citrus growers are taking to stay profitable in the era of citrus greening is to look to high-density plantings. In the past, citrus groves were planted at a density of around 100 trees an acre, and the trees produced fruit for decades. Today, citrus trees are facing a near-100 percent citrus greening infection rate with, meaning they only have a small window where they will be productive. Once the disease starts to affect production, the tree is removed and replanted. To boost production, it makes sense to try out planting more trees in the same area. Planting density trials are ongoing at the Indian River Research and Education Center, and they suggest that high-density plantings could have real benefits for growers.
Details of Planting Density Trials
The planting density trials underway at the Indian River Research and Education Center (IRREC), are being led by Assistant Professor of Citrus Horticulture, Dr. Rhuanito Soranz Ferrarezi. The trials have been underway since 2017, and one of the objectives (among others) was to identify the best tree planting spacing for higher tree growth and yield.
Two-year trials have been completed thus far. Each trial looked at the production of trees planted at 119 trees per acre, 173 trees per acre, or 393 trees per acre. Both trials found that higher tree planting density increases fruit yield and fruit quality. They also found that staggered (a necessity of the raised beds at IRREC), high-density plantings produced more soluble solids per area.
Ferrarezi did maintain that the highest end of the high-density plantings had a yield that was too low due to poor rootstock performance/choice (Kuharske citrange). He points to a concept of the “sweet spot,” meaning each different scion/rootstock combination will have a different planting density point where spacing will be optimal for the tree to achieve maximum production; after that point, fruit production will likely suffer.
Research has shown that citrus trees will continually try to regain their natural shape despite pruning and the like, and they will focus on vegetative production at the cost of fruit production. There are also other factors, like in-place irrigation systems and harvesting machinery to consider. The “sweet spot” concept posits that in-row spacing, between-row spacing, and the tree vigor of the scion/rootstock combination chosen for planting all need to be considered when planning a high-density grove.