Conventional sphagnum peatlite substrate can be reduced by 50% in stratified substrate systems while growing equivalent size and quality Pentas lanceolata

Authors: FIELDS, JEB - Louisiana State University Agcenter; CRISCIONE, KRIS - Louisiana State University Agcenter; Owen Jr, James - Jim

Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2024
Publication Date: 3/29/2024
Citation: Fields, J.S., Criscione, K.S., Owen Jr, J.S. 2024. Conventional sphagnum peatlite substrate can be reduced by 50% in stratified substrate systems while growing equivalent size and quality Pentas lanceolata. Scientia Horticulturae. 331. Article 113121. https://doi.org/10.1016/j.scienta.2024.113121.
DOI: https://doi.org/10.1016/j.scienta.2024.113121

Interpretive Summary: Floriculture crop production is a multibillion-dollar industry ($5.5 B) with increased annual sales over the previous two decades. Soilless substrate serves as the fundamental pillar in successful specialty crop greenhouse production. The basic roles of soilless substrates are to 1) provide anchorage and support for growth and development, 2) store water and mineral nutrients for uptake and acquisition in physiological and metabolic processes, and 3) facilitate gas exchange. Peat has become the gold standard of soilless substrate components, with the global horticultural industry relying primarily on peat substrates (e.g., Europe’s greenhouse operations are 75% peat-based). Global peat use is increasing as growers transition from field production into soilless culture and is predicted to double by 2050, with overall substrate requirements estimated to increase 400% in that same timeframe. Soilless substrate stratification is one technique described to extend existing peat supply. Stratification entails the vertical layering of different soilless substrates within a container. Generally, a finer or fibrous media is stacked atop a coarse substrate. The objective of this research was to optimize growth of a popular floriculture crop, Pentas lanceolata Forrsk. (Egyptian Star Flower), in stratified substrate systems with varying depth of the top portion of the vertical profile (i.e., increasing proportions of sub-strata bark) to extend peat. The lower portion of the vertical profile was inexpensive by-product of the timber industry, aged loblolly pine (Pinus taeda L.) bark, that is readily available in the Southeastern U.S. The results showed that a crop of equal quality to a traditionally grown pentas (i.e., 100% peatlite) can be grown when the peat depth layer is greater than 9 cm or 50% (by vol.) of an 18 cm container. Pentas growth and development was significantly reduced when grown in a stratified container with only 5 cm or 25% (by vol.) of peatlite over 13 cm or 75% (by vol.) aged pine bark, which is hypothesized herein to the result of decreased substrate water storage and delivery to crop roots. This study demonstrates that a popular floriculture crop can be grown by stratifying expensive floriculture media above inexpensive aged pine bark with little to no differences in growth if the stratified layer is equal or greater than half the container height.

Technical Abstract: Floriculture crop production heavily relies on the use of peat-based substrates to quickly mass produce containerized crops. The sustainability of using peat moss has been an increasing concern for both horticultural stakeholders and the community. The concept of stratifying soilless substrates (i.e., vertically layering unique substrates atop of each other within the container) has been shown to reduce peat moss applications by upwards of 50%. Although, most stratified substrate research has only studied an equal partition in which the substrate is evenly split into two layers. This necessitates further studying modification of the limits and optima for the depth of each layer. This study evaluated adjusting this stratified depth layer for possible further benefits, such as reduced water and peat moss applications. Lucky Star Dark Red Pentas lanceolata ‘PAS1231189’ was grown in one of four substrate treatments, including a (1) non-stratified 100% peat and perlite blend (peatlite), (2) 13.4 cm peatlite placed above 4.4 cm pine bark (PB) horizon with the container consisting of 75% (by vol.) peatlite and 25% (by vol.) PB; (3) 8.9 cm peatlite placed above 8.9 cm PB layer with the container consisting of 50% (by vol.) peatlite and 50% (by vol.) PB; (4) 4.5 cm peatlite placed above 13.3 cm PB with the container consisting of 25% (by vol.) peatlite and 75% (by vol.) pine bark. Crops were placed on irrigation-actuated lysimetry systems to maintain substrate volumetric water contents between 0.20 to 0.30 cm3 cm-3. This study identified successful production of pentas in stratified profiles when the depth layer is = 50% peatlite by vol., with equal growth to pentas grown traditionally (i.e., 100% peatlite; non-stratified). However, crops grown in a 25% peatlite : 75% PB depth layer experienced significantly reduced growth with regards to growth index, quality, and dry biomass. Moreover, crops grown in the 25% peatlite by vol. also experienced faster peak inflorescence with a subsequent continuous decline in flower development due to water stress; whereas, plants grown in = 50% peatlite by vol. continued to develop blooms throughout the study. This study demonstrates that a popular floriculture crop can be grown by stratifying expensive floriculture media above inexpensive PB with little to no differences in growth if the stratified layer is equal or greater than 50% the container volume.