The rate of growth of transplanted trees is generally misunderstood. This misunderstanding has given to the notion that a small transplant over time usually outgrows a larger transplanted tree.
1985 W.T. Watson hypothesized that smaller transplanted trees could quickly surpass in size larger transplanted trees. This was based upon estimates and modeling and assuming equal rate of growth of roots for small and large trees, but not much science. This has been passed on as gospel, both in the classroom, and in the industry. But science does not bear this out.
The time for roots to re-establish depends upon the size of the root-ball harvested, soil preparation, and aftercare. Root elongation in the northern states ranges from 11.8 to 23 inches per year (Coutts, 1983; Gilman 1988, and Watson et all 1986). So it is that the root ball diameter can increase at least 4 feet per year, and become the size of the canopy diameter within 2-3 years.
These rate of growth is without the benefits of modern root stimulation techniques.The time for roots to re-establish depends upon the size of the root-ball harvested as a proportion to the trunk diameter, soil preparation, and aftercare. Most studies were/are based upon ANSI standards, which are provide at best marginal root balls (a mere 9 inches of root ball per caliber inch of trunk). Times have changed since 1985. Big tree-spades of that day were usually 45 inch diamenter, and asked to perform heroic feats. Today are frequently much larger than 29 years ago. Tree spades now can deliver (4,000 lb to 12,000 lb root balls). And at Trees on Wheels our customary root-ball not 9 inches of root-ball per caliper inch, but 12-15 inches of root-ball per inch of trunk.
And These “studies” were performed before the following root stimulation principles were understood.
Later Watson has changed his mind. Watson now concedes that The Struve study (2000) suggests that smaller trees will not outgrow the larger transplants, and now publishes that “Additional long term studies need to be conducted to determine how establishment rates of various sized trees affect the long term growth rates of transplanted trees”.
January–March 2005 15(1)WORKSHOP Influence of Tree Size on Transplant Establishment and Growth by W.Todd atsonwww.mich.gov/.../Influence_of_Tree_Size_on_Transplant_Establishment_Watson, 200
Because root growth is “pushed” by the photosynthesis of the existing canopy, it would seem larger canopies would accelerate root elongation. Some articles suggest this is not the case. However our larger root-balls, root stimulators, hereinafter described, deep roto-tilling, with the aftercare we suggest you can have a root mass that approximate the drip-line of your new tree in 2-3 years.