Soilless substrate stratification has developed into a powerful substrate management strategy for containerized crop production globally. The product entails layering substrates with unique physiochemical properties atop each other to improve production sustainability and costs. Originally, the concept was aimed for nursery production, layering fine bark or bark amended with fibrous materials atop coarse bark, to improve moisture balances and reduce fertilizer/ irrigation applications/ costs. However, recent research has highlighted stratification as an effective tool to significantly reduce peat use and reliance in the horticultural industry. To expand, layering a high-performance peat-based substrates atop inexpensive and abundant substrate components or composites can produce similar or better-quality plants, while significantly improving production sustainability (reduction in peat applications and associated costs). This concept was originally explored with pine bark as a “filler” material in the bottom strata to grow petunia, cutting commercial peat-based substrate by upwards of 50% (by vol.) while producing equal quality plants. As this research line persists, further refining the filler materials to utilize more regional agricultural biomass and fibers (i.e., various wood fibers, sugarcane bagasse, biochar, etc.) can continue augmenting production sustainability. Current research has produced high-quality and salable crops in refined stratified systems, incorporating these alternative substate materials in the top-half to further extend peat reserves, or installing the materials as stand-alone in the bottom-half, ultimately improving moisture and mineral nutrient balances and significantly reducing peat-based substrate volume applications and expenses. Overall, this line of research has resulted in the ability to strategically deploy regional biomass materials into soilless production systems without losing plant quality. Furthermore, utilizing the stratified systems results in improved water and nutrient efficiency.

Stratified growing media means arranging growing media in layers in pots. Compared to traditional growing media mixtures, working with two or more layers allows the user to put coarser material in one layer and finer material in the other layer which (i) allows the use of a higher level of peat alternatives and (ii) decreases the natural gradient in water content from top to bottom. This trial aimed to test stratified growing media for potted spathiphyllum under ebb-and-flood fertigation. Two factors included growing media and fertigation regimes. Pots were filled with two layers of growing media mixtures to include a higher proportion of renewable growing media such as sphagnum moss, wood fibre, bark, and miscanthus. These mixtures require adaptation in base dressing and fertigation. Stratification by replacing the bottom half of the peat-based reference substrate performed similarly to the original peat-based substrate under normal fertigation conditions. When both the top and bottom layers of the peat-based reference substrate were replaced with renewable resources, performance was lower compared to peat. Modifying the fertilization improved performance, but the degree of difference and improvement depended on the proportion of less stable raw materials used in the mixture. This study provides valuable knowledge to increase the use of renewable growing media for potted ornamentals.

Soilless substrates are responsible for maintaining a healthy container rootzone to support both prolific root growth and productive shoot performance/ yield. More scientific reports demonstrate that the health and integrity of the root systems (1) are strongly influenced by the substrate physiochemical properties and (2) significantly affect shoot development. Despite these known relationships, most horticultural research to-date is directed towards shoot productivity, excluding important root growth metrics upon experiment culminations (i.e., root morphology or surface features; root architecture or spatial configuration), usually only encompassing root biomass measurements. While more specialty crop production practices transition to containerized systems, its important to develop a stronger understanding in how soilless substrates impact container root growth and development and vice versa. Thus, the research herein investigated relationships between substrate hydraulic properties and root morphological, hydraulic, and architectural growth when grown in conventional and engineered substrates (screened bark or stratified substrates; layering substrates with different physical properties atop each other). In an overarching sense, stratified substrates enhanced root morphological growth, producing longer root lengths and greater volumes/ surface areas, as well as greater fine root development, especially in the top strata layer. Plants grown in substrates with greater water transfer properties typically contained the aforementioned morphological features. With regards to root architecture, stratified substrates induced a more “shallow” root system, with wider root distribution angles. Moreover, research herein demonstrated that stratified-grown roots grow sequentially, exploring and filling the top half longer before proliferation into the sub-strata. Considering substrate hydraulic properties, stratified substrates have more moisture uniformity and faster oxygen supply to the container rootzone, possibly explaining the enhanced root growth. Active root growth and presence in substrate profiles influences how moisture is stored and drained, where partially rooted systems store more water and greater root system volumes increase drainage. In all, this research provides novel techniques for horticultural root growth research to better understand container root-substrate interactions.