Effects of Container Substrate Composition on the Growth and Performance of Garberia heterophylla (W. Bartram) Merr. & F. Harper: A Native Xeric Species

Container production of landscape plants requires reliably consistent and affordable substrates with properties suitable for a wide range of species. Native plant production often requires additional considerations when determining ideal substrates for species found in precise ecosystems. Thus, the introduction of novel native species, such as garberia [Garberia heterophylla (W. Bartram) Merrill & F. Harper] requires research insight into discerning which type of substrate provides the greatest plant quality in the least amount of time. In this greenhouse study, garberia was container-grown for six months in five substrates. These included two different pine bark-based media (Atlas 3000 and ‘Native mix’) typically used for native plant production, a commercial standard of peat-based medium (ProMix BX), and compost-based medium (COMANDscape) by itself or at a 1:1 compost/native mix ratio. All substrates varied from each other in terms of pH and electroconductivity (EC), with ProMix BX having the most acidic pH (5.3) and COMANDscape having the highest EC (5.2 dS/m). The ProMix BX had the greatest water-holding capacity, while the Atlas 3000 had the greatest bulk and particle densities. After six months, plant heights and widths were similar between treatments. The ProMix BX yielded the greatest shoot and root dry matter values and well-developed root systems that held the substrate the best. Plants grown in ProMix BX or COMANDscape had the greatest SPAD values and very good to excellent shoot visual quality ratings, compared to other substrates evaluated. While garberia was found to be a slow-growing species regardless of substrate, these results demonstrate its tolerance of diverse substrates that are non-characteristic of the soil where it thrives naturally. This knowledge can be useful for nursery practitioners; ultimately contributing to expanded production and the widened use of garberia in landscapes.