The ornamental production industry utilizes either controlled greenhouse or open-air nursery production systems. Both rely upon the use of soilless substrates, with regular application of water and mineral nutrients, to maintain profitability and quality crop growth and development. However, the leading base substrates components used, peat moss and bark, present sustainability concerns for producers. Peat moss sustainability concerns surround harvest, supply, and cost (environmental, social, and economic; three tiers of sustainability) of the material. Pine bark sustainability in production is due to inefficiency in water and mineral nutrient retention (environmental, social, and economic). Nevertheless, a solution to help improve the sustainability of both substrates across the greenhouse and nursery industry has developed. Soilless substrate stratification is a practical management strategy that entails layering two unique substrates, either derived from the same substrate or different substrates, atop one another in the container. Stratifying substrates has been shown to reduce peat use and reliance in the greenhouse industry by upwards of 50%. Moreover, stratifying substrates can reduce irrigation and fertilizer applications by 25- and 20%, respectively. To date, stratified substrate research has utilized an even 50:50 stratified depth layer partition. As growers adopt this technique, more understanding of the balance and opportunities is needed. Thus, a series of experiments was developed to explore varying ratios of stratification. In two experiments, popular greenhouse (Petnas) and nursery (Rosa) crops were grown in different stratified depth layer ratios with peat-based (greenhouse) and bark-based (nursery) systems. Ratios included a non-stratified treatment (100% filled), a 75:25 percent by vol. layer partition, a 50:50, and a 25:75. In the greenhouse experiment, peatlite mix was layered over unscreened bark and irrigation was lysimeter-actuated. In the nursery experiment, fine bark particles were layered over coarse particles. Moreover, different fertilizer rates were applied (low, medium, high). The results showed in the greenhouse study, a Pentas crop can be grown with equal growth (and similar quantities of water) as traditional greenhouse crop when ≥50% peatlite is used by vol. In the nursery experiment, low fertilizer application rates can be used to grow a crop similar to a traditional nursery-grown crop when grown in a stratified system. While there are discrete differences, it primary take away is that stratification does not need to be overly technical to generate impact and improve efficiency; however, there is a limit to the ability to use “filler” material which tends to be about 50% of the volume.
