Increasing the efficiency of irrigation practices is necessary to conserve water resources. However, extreme reductions in irrigation may lead to stunted growth. In this project, we aimed to evaluate if chitosan applied as a substrate amendment influenced plant growth, physiology, and marketable parameters of container-grown ornamental crops cultivated at different container capacities. The experiment was a full-factorial design with two factors: container capacity (100%, 70%, and 40%) and chitosan application timing (No application, Week 1, Week 3). The plants were kept in the greenhouse for six weeks and then in growth chambers set at 30°C or 40°C for two weeks to simulate post-production conditions. Plant growth and stomatal conductance were measured weekly and flower area after the sixth week. Significant differences were observed between the treatments. Plant growth was lowest at 70% and 40% CC when chitosan was applied at week 3. The stomatal conductance of plants under 70% and 40% CC was higher than 100% CC with no chitosan, but plants with chitosan at 40% CC had higher stomatal conductance. Flower coverage did not differ at the end of the crop cycle and in the first week at the two post-production temperatures (30°C and 40°C), but in the second week, the flower coverage decreased drastically in all the treatments, with the lowest values observed at 100% CC in both environmental temperatures. Deficit irrigation in petunia plants could be a strategy to produce marketable plants while reducing the volume of water. Chitosan applied in the first week of production seems to be the best application timing under deficit irrigation to see an amelioration effect from lowering container capacity.
