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Inhibition of Transplanted-Tree Growth by Grass

Inhibited growth of trees transplanted in grassed areas is a phenomenon that has been noted time and again by various
horticultural researchers. It is one of the major reasons for mulching around trees. But just how much difference in tree growth can grass make? A lot, according to field trials conducted at Kansas State University. Eastern redbud (Cercis canadensis) and pecan (Carya illinoinensis) seedlings were transplanted into plots with tall fescue, Kentucky bluegrass, Bermuda grass, no vegetation (maintained with herbicide treatments), or three inches of organic mulch. All plots were fertilized as per recommendations for the location, and at least one inch of water was applied per week during the growing season. At the end of the second season following transplanting, redbud and pecan caliper six inches above the ground averaged about twice as large without grass as
with either fescue or bluegrass, and it averaged about 50% larger without grass as with Bermuda grass. Average weight of the tops of redbuds was boosted by about 300% and average weight of pecans was boosted by about 200% in no grass plots, relative to plots with grass. Average leaf area of the trees went up by about 200% and leaf weight went up by 300% in plots without grass, relative to the grassy plots. Growth of redbuds in plots with fescue and bluegrass had ceased in the middle of August in the second season following transplanting, while growth of redbuds in no-grass plots was continuing. The researchers who conducted the trials contend that resource (water and fertilizer) competition was not likely to be the sole reason for the difference in tree growth due to the presence of grass. One possible additional factor is inhibition of tree growth due to chemicals released by the grasses; the researchers suggest that inhibition of tree growth might be exacerbated by "the current trend" of breeding grass cultivars that are highly weed-suppressive

Reference: Jason J Griffin 9John C Pair Horticultural Center, 1901 E 95th St South, Haysville, KS 67060), William R Reid, and Dale J
Bremer, "Turf Species Affects Establishment and Growth of Redbud and Pecan", HortScience 42(2), April 2007, 266-271.
(American Society for Horticultural Science, 113 S. West St., Suite 200, Alexandria, VA 22314-2851.)

Click here to request a copy of the full report in PDF file format.  Inhibition of Transplanted-Tree Growth by Grass

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