Dr Desmond Layne, associate professor of pomology, tree fruit specialist, and state program team leader for horticulture at Clemson University

Stone Fruit

Tree Density and Profitability

Desmond R. Layne
dlayne@clemson.edu

So you have heard at your recent winter meetings that growing peaches high density is “the way to go” and you are interested in learning more.  Or perhaps you are struggling with the idea of learning a new concept and the increased tree cost per acre that comes with high density. Maybe you are quite happy with the production system you have and you are interested in simply making it more productive and profitable.

I am a believer in the concept, “if it ain’t broke, don't fix it!”  In terms of peach orchard management, this may be a gross oversimplification, but my position is never to force my preconceived ideas on any producer.  I would rather share accurate information with a goal of helping the grower to see his options and make well-informed decisions that are best suited for his/her operation.  So what about high density anyway?  Is it worth it?  Does it pay?

Five Key Points

Simple questions often dictate rather lengthy and complicated answers.  First, the term “high density” means different things to different people.  If you currently have trees spaced at 100 to 130 trees per acre, you may consider high density simply doubling the number of trees per acre.  Others may say that you are not actually “high density” until you have more than 400 trees per acre.  Because peach growers do not have access to strongly dwarfing rootstocks like those used in apple production, we do not achieve anything near what many apple growers would consider to be “high density.”

Second, if you plant higher density, your orchard establishment costs may escalate substantially.  In addition, you may need to learn a new system of tree training and pruning (i.e., KAC perpen- dicular-V) that requires summer pruning to be viable.  This is no small consideration.  It requires skilled labor and attention to detail, and timing is very important.  In the case of V-shaped trees, in particular, if summer pruning is done too late in the season, flower buds may not be produced and cropping next year added cost of summer pruning, we have found in our long-term trial at Clemson University that summer-pruned trees require much less dormant pruning (a cost savings).  Further, summer pruning improves light distribution in the canopy that results in improved fruit size and coloration.

Third, one advantage of higher density is that trees fill in the row sooner in the life of the orchard.  Under normal circumstances, yield per acre will be higher in the early life of the high-density orchard compared with the conventional one.  This increased early yield may help to offset the cost of the additional trees.  Once the trees fill the tree row, the orchard is absorbing as much sunlight as it can.  Most researchers have noted that once the tree row is filled in, yield differences between orchards with different tree densities and training systems may be negligible.

Fourth, tree height may vary depending on the tree density and system used. In our trial at Clemson, the conventional, low-density, open-center trees were maintained to 8 feet while the medium and high-density V systems were grown to 12 feet.  A disadvantage of the taller trees is the necessity for ladders to prune, thin, and harvest.  In Italy, some growers use self-propelled picking platforms.  Taller trees can be advantageous during freeze events like we had one year at our research farm.  On that occasion, we found that all flower buds from 5 feet high to the ground were killed.  For our conventional, low-density, open-center trees, this reduced the potential crop by more than 50% while the crop in the “V” trees was reduced by only 20% because the trees were much taller.

Fifth, with the high-density “V” systems (KAC perpendicular-V, in particular), a very significant advantage is the fact that nearly every tree down the row is identical in form.  Although ladders may be necessary, each primary scaffold can be reached essentially from one ladder position.  Thus, pruning, thinning, and harvesting operations are quite simple and one laborer can move the ladder once each from tree to tree proceeding down the row.

Watch For Rot

One concern that I have for the southeastern U.S. is the prevalence of oak root rot disease (Armillaria spp.). I have visited orchards in South Carolina where as many as 20 adjacent trees down the row all died in one to two years time.  With trees planted so closely, root systems of trees intermingle quickly and root grafts often occur between adjacent trees.  This is a problem because Armillaria can bridge a root graft and lead to the steady progress of infection down a tree row.  This process is much slower for trees that are spaced 20 feet apart when compared to those spaced only 6 feet apart.

Other Considerations

As you consider trying higher density plantings, here are some tips:

  • Do your homework ahead of time
  • If possible, visit someone who has been successful
  • Start on a small scale and learn how to manage the system first
  • Choose varieties that have the genetic potential to be large
  • Understand that summer pruning cannot be neglected or occur too late
  • Don’t plant high density if the site has high risk or history of oak root rot disease
  • If the orchard is to be pick-your-own, tree height may be a concern because ladder use increases liability.

Finally, any decision to change what you are currently doing must take into consideration your existing equipment and labor force.  It takes time to train pruning crews to manage a system that they are unfamiliar with.  Can you justify the increased cost of trees during the establishment phase?  Is the availability and cost of land a concern such that you need as high a profit as early as possible?  If so, high-density plantings might provide a good option.  Feel free to contact me by e-mail if you have questions!

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This column by Dr. Desmond R. Layne, “Tree Density and Profitability”, appeared in the January 2007 issue of The American Fruit Grower magazine on page 36.

Desmond R. Layne, Ph.D., is an associate professor of pomology, tree fruit specialist, and state program team leader for horticulture at Clemson University. He is also president of the American Pomological Society.

For more information, go to www.clemson.edu/peach.