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

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 (peat-lite), (2) 13.4 cm peat-lite placed above 4.4 cm pine bark (PB) horizon with the container consisting of 75 % (by vol.) peat-lite and 25 % (by vol.) PB; (3) 8.9 cm peat-lite 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 peat-lite placed above 13.3 cm PB with the container consisting of 25 % (by vol.) peat-lite and 75 % (by vol.) pine bark. Crops were placed on irrigation-actuated lysimetry systems to maintain substrate volumetric water contents between 0.20 and 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 % peat-lite; non-stratified). Crops grown in a 25 % peat-lite : 75 % PB depth layer experienced significantly reduced growth with regards to growth index, quality, and dry biomass. Moreover, crops grown in the 25 % peat-lite 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 peat layer is equal or greater than 50 % the container vol.