Reducing post-harvest losses of tomatoes and onions remains crucial for income and food security in the Guinguineo department. The objective of this study is to analyze the effectiveness of storage and preservation practices to maintain the freshness of the produce. A survey was conducted among stakeholders regarding existing storage and preservation techniques in the area. Two batches were studied for each crop: one harvested using compost and the other harvested using chemical methods. For each batch, two preservation methods were tested: the traditional method (the existing method) and a new, improved approach to determine which could be recommended to stakeholders. The results showed that for tomatoes, after 20 days, the improved method for composted tomatoes preserved 25 fruits compared to 18 for the traditional method. For chemically treated tomatoes, the improved method preserved 33 fruits compared to 23 for the traditional method. Regarding onions, after 3 months, production under compost combined with the improved method plus ash shows the lowest weight loss (0.11 kg). For chemical production, storage in perforated bags is the most efficient with a loss of 0.38 kg.