This study aimed to evaluate the effect of canna (ganyong, Canna edulis Ker.) starch-based edible coating on the postharvest quality of tomatoes and to determine the optimal starch concentration for shelf-life extension. The novelty of this research lies in the application of ganyong starch—a locally underutilized Indonesian tuberous crop with high amylose content (32.53%)—as a functional edible coating matrix. The study employed a Completely Randomized Design (CRD) with five treatment levels (P0: control/no coating; P1: 1% w/v; P2: 1.5% w/v; P3: 2% w/v; P4: 2.5% w/v ganyong starch) and three replications, yielding 15 experimental units each consisting of five uniform tomato fruits (75 fruits total). Prior to ANOVA, data normality was verified using the Shapiro–Wilk test and variance homogeneity was confirmed using Levene's test. Analysis of Variance (ANOVA) followed by Duncan's New Multiple Range Test (DNMRT) at the 5% significance level was applied independently at each observation day (days 0, 4, 8, 12, 16, and 20). Results demonstrated that the 2.5% w/v ganyong starch coating (P4) was the most effective treatment, significantly reducing weight loss (12.41%), maintaining firmness (4.16 kgf/cm²), stabilizing pH within the physiological range (4.00), and preserving vitamin C content (4.40 mg/100 g) relative to the uncoated control. Hedonic evaluation (30 panelists) gave the 2.5% coating the highest acceptance scores for firmness (3.13, "somewhat like") and color (3.00, "somewhat like").