  Citation: Regmi, A.; Singh, S.; Moustaid-Moussa, N.; Coldren, C.; Simpson, C. The Negative Effects of High Rates of Biochar on Violas Can Be Counteracted with Fertilizer. Plants 2022, 11, 491. https:// doi.org/10.3390/plants11040491 Academic Editors: Othmane Merah, Purushothaman Chirakkuzhyil Abhilash, Magdi T. Abdelhamid, Hailin Zhang and Bachar Zebib Received: 26 January 2022 Accepted: 7 February 2022 Published: 11 February 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). plants Article The Negative Effects of High Rates of Biochar on Violas Can Be Counteracted with Fertilizer Abishkar Regmi 1 , Sukhbir Singh 1 , Naima Moustaid-Moussa 2,3 , Cade Coldren 1 and Catherine Simpson 1, * 1 Department of Plant and Soil Science, Texas Tech University, Lubbock, TX 79409, USA; abishkar.regmi@ttu.edu (A.R.); s.singh@ttu.edu (S.S.); cade.coldren@ttu.edu (C.C.) 2 Department of Nutritional Sciences, Texas Tech University, Lubbock, TX 79409, USA; naima.moustaid-moussa@ttu.edu 3 Obesity Research Institute, Texas Tech University, Lubbock, TX 79409, USA * Correspondence: catherine.simpson@ttu.edu Abstract: Increasing costs and environmental issues regarding excessive use of peat moss is impacting the horticultural industry. Biochar is a valuable substrate additive that has the potential to reduce the use of peatmoss in greenhouse production. However, its varying effects on ornamentals requires that individual species and cultivars of crops must be evaluated to determine the threshold for benefits. Viola cornuta is a high value ornamental crop; however, information on how different rates of biochar rates affect productivity and physiology of Viola cultivars in container production is not known. To determine if biochar rates could increase the productivity of Viola, we mixed a peat-based substrate with 10, 25, and 50% (w:w) hardwood biochar in two studies on four cultivars. Without fertilizers, 10 and 25% biochar improved plant biomass, growth, root length, and flowering, but 50% biochar was found to have negative effects on plant growth and flowering. Cultivars varied in their response to biochar rates. When fertilizer was applied in the second experiment, biochar rates did not impact growth parameters or flowering. These results suggest that up to 25% biochar can be used in Viola production without detrimental impacts. However, 50% biochar can be used with the addition of fertilizer without negatively affecting plant growth. Biochar can have a short-term impact on the growth characteristics of Viola plants in container production, but fertilization and growing period of Viola may influence these effects. These results indicate that biochar could be the suitable replacement for peat moss, with up to 50% biochar rate in Viola production reducing the environmental and economic burden for peat moss. Keywords: biochar; Viola; ornamental; physiology; containers; production 1. Introduction Peat moss is one of the main components of soilless potting mixes used in container production in commercial greenhouse industries. Horticultural crops use around 11 million kilograms of peat moss annually [1]. Due to adverse environmental pressure and high rates of peat extraction, alternatives for peat moss are needed [2]. Most of the peat is extracted in Canada and transported to the US, increasing the shipping and handling cost [3,4]. Therefore, different organic and inorganic soil additives are now being substituted for portions of this growing media [5,6]. Biochar is being increasingly explored in production due to its many beneficial properties [5,7]. Biochar is a charcoal-like carbon rich substance obtained from pyrolysis of plant material or organic waste in an anoxic environment [8–10]. The particle size, quality, and toxicity of biochar differs by the methods used, substrate, and temperature applied during the manufacturing process [11–13]. Because of biochar’s high porosity and surface/volume ratio, it can retain high amounts of exchange cations, resulting in higher adsorption to the planting medium and better productivity of crops [14,15]. As a result, biochar has been Plants 2022, 11, 491. https://doi.org/10.3390/plants11040491 https://www.mdpi.com/journal/plants