Container type affects nursery production, landscape establishment and irrigation requirements of woody plants

Abstract

The black plastic (BP) pot is the container most used for nursery tree and shrub production. While there are many advantages to producing woody plants in BP containers, a major disadvantage to their use is that circling, girdling and matted roots often form during production and high substrate temperatures can injure or kill roots. The compromised root systems of BP-grown plants can lead to short- and long-term problems following planting in the landscape. We compared the growth of Pyrus calleryana Decene. 'Glen's Form' (Chanticleer®) in three container types: black plastic, Root Pouch® (RP) and Smart Pot® (SP), in the nursery over two growing seasons and under two overwintering treatments (consolidated or lined out), and planted into the landscape for three growing seasons. After the first growing season in the nursery, there were no differences in height or dry leaf, shoot and root weight among the three containers. Following the second growing season, caliper, height, leaf area and root ball quality differed among container type were significantly greater for plants grown in the two fabric containers. After the 2010-2011 winter, consolidated trees produced larger root and shoot systems (35.3% and 36.4%, respectively) than trees that were lined out. Substrate temperature maxima and fluctuations during winter and summer were greatest for BP containers compared to RP and SP. After nursery-grown trees were transplanted into the landscape, we found no container effects on above-ground growth one, two and three years following transplant into the landscape. All trees, regardless of container type, doubled their root dry weight annually over the three-year study. We found no significant container effects for any measured root parameters one year after planting. However, two and three years following planting we found a greater percentage of total root growth beyond the original root ball for trees grown in RP and SP containers. Three years after planting, trees grown in BP containers had significantly more fine roots growing within the original root ball compared to RP- and SP-grown trees. There were no significant differences among container type for leaf water potential one and two years following planting. In a four week greenhouse study, BP containers lost half as much water as the fabric containers. Water loss from the two fabric containers was significantly more rapid than that of the BP containers during the first 11 days, with more gradual water loss occurring thereafter. Total potential evapotranspiration (PET) for fabric containers containing established Viburnum trilobum was greater than that of BP-grown plants. When irrigated at 75% of black plastic PET (BP-PET), the cumulative ET for RP-grown plants over a two weeks period was significantly lower than that of BP or SP; at 50% of BP-PET, there were no container effects on ET. These results suggest that newly planted fabric containers (where water loss is mostly evaporative and not transpirational) may require greater irrigation needs than plants growing in BP containers. However, as plants in containers become more established and container water loss becomes more a combination of evaporation and transpiration, plants growing in fabric containers may have irrigation needs similar to or less than that of plants growing in BP containers.