Placing organic mulch over the root system of newly planted trees is common landscape practice. Mulch helps conserve soil moisture, moderate extremes in soil temperature, reduce competition for resources from weeds and turf, and minimize trunk injury due to lawn mowers and string trimmers (Hartman et al., 2000; Lloyd, 1997).
Similar to a natural woodland situation where tree fine roots grow close to the surface, the roots of newly planted, bare-root sugar maple (Acer saccharum Marshall) developed in a similar manner when organic mulch was applied (Green and Watson, 1989). In that report, 40% of the harvested root density was found in the upper 5 cm of soils covered with organic mulch. But when covered with turfgrass sod (no mention of grass species), root development was practically nonexistent in the upper 5 cm and overall root production was less than 33% of the trees that had mulch applied.
Whitcomb (1981) observed that overall growth and appearance of selected woody ornamental species decreased in the presence of bermudagrass (Cynodon dactylon). However, when planted in a 76 cm square area cleared of bermudagrass, plant growth and appearance was improved. No mulch was applied in that study, which suggests some interference of bermudagrass on establishment and growth of newly planted ornamentals. In contrast, annual shoot and stem caliper growth of honeylocust (Gleditsia triacanthos L.) were similar over two growing seasons between plots covered with bermudagrass and plots with a 60 cm diameter clearing maintained around the trunks (Khatamian et al., 1984). These studies suggest that the effects of bermudagrass on the establishment and growth of landscape trees is unclear.
Root growth of established trees also benefits from the removal of turfgrass and the addition of mulch. Watson (1988) showed that root density of various 20-year-old trees increased when sod was replaced with a 10 cm layer of mulch or simply left as bare soil. The most dramatic response was in the upper 15 cm of soil, where the density of fine tree roots increased by at least 50% in all but one species.
Turfgrasses may have an allelopathic effect on woody landscape plants. Recent research has shown that various species of fine fescue (Festuca spp. L.) inhibit seedling growth of large crabgrass [Digitaria sanguinalis (L.) Scop.] and cress (Lepidium sativum L.) (Bertin et al., 2003). In other studies, tall fescue (Festuca arundinacea) inhibited the growth of nearby plants including some trees (Gilmore, 1977; Larson et al., 1995; Peters and Luu, 1985; Smith et al., 2001). Tall fescue is one of the most common turf species used in the landscape industry. Replacing turf with mulch may reduce allelopathic effects on tree establishment and growth. Recent reviews have discussed plant allelopathic interactions and their potential beneficial use in the landscape (Bertin et al., 2003; Weston, 2005; Weston and Duke, 2003).
The objective of the current research was to determine if three common turfgrass species used throughout the southern Great Plains inhibit establishment and growth of eastern redbud (Cercis canadensis) and pecan (Carya illinoinensis). Eastern redbud was selected due to its indeterminate growth habit, common use as a landscape plant, and responsiveness to environmental changes. Pecan was selected because its response to tall fescue sod has been well established in the literature. While the influence of turf on tree establishment has been explored by others, none have examined more than one grass and also included a mulch and bare soil treatment. Additionally, few projects have examined more than one tree species. This report attempts a more expansive look at the influence of turfgrass on landscape tree establishment and growth.
Bertin, C., Paul, R.N., Duke, S.O. & Weston, L.A. 2003 Laboratory assessment of the allelopathic effects of fine leaf fescues J. Chem. Ecol. 29 1919 1937
Bremner, J.M. & Mulvaney, C.S. 1982 Salicylic acid thiosulfate modification of the Kjeldahl method to include nitrate and nitrite 621 Miller R.H. & Keeney D.R. Methods of soil analysis. Part 2 Am. Soc. Agron., Inc Madison, Wis
Gieseking, J.E., Snider, H.J. & Getz, C.A. 1935 Destruction of organic matter in plant material by the use of nitric and perchloric acids Ind. Eng. Chem. Anal. Ed. 7 185 186
Green, T.L. & Watson, G.W. 1989 Effects of turfgrass and mulch on the establishment and growth of bare-root sugar maples J. Arb. 15 268 272
Khatamian, H., Pair, J.C. & Carrow, R. 1984 Effects of turf competition and fertilizer application on trunk diameter and nutrient composition of honeylocust J. Arb. 10 156 159
Larson, M.M., Patel, S.H. & Vimmerstedt, J.P. 1995 Allelopathic interactions between herbaceous species and trees grown in topsoil and spoil media J. Sustain. For. 3 1 39 52
Peters, H.C. & Luu, K.T. 1985 Allelopathy in tall fescue 273 283 Thompson A.C. Chemistry of allelopathy: biochemical interactions among plants ACS Washington, D.C
Smith, M.W. 1991 Pecan nutrition Wood B.W. & Payne J.A. Pecan husbandry: challenges and opportunities 1st National Pecan Workshop Proc USDA-ARS Pub ARS-96. 259 pp
Smith, M.W., Cheary, B.S. & Carroll, B.L. 2004 Response of pecan to nitrogen rate and nitrogen application time HortScience 39 1412 1415
Smith, M.W., Wolf, M.E., Cheary, B.S. & Carroll, B.L. 2001 Allelopathy of bermudagrass, tall fescue, redroot pigweed, and cutleaf evening primrose on pecan HortScience 36 1047 1048
Thomas, R.L., Sheard, R.W. & Moyer, J.R. 1967 Comparison of conventional and automated procedures for nitrogen, phosphorus, and potassium analysis of plant material using a single digestion Agron. J. 59 240 243