Patients often experience emotional distress after acute coronary syndrome (ACS). These may lead to symptoms of depression or anxiety and greater morbidity/mortality. We sought to determine whether flowering plants in the coronary care ward reduced depressive and anxiety symptoms in these patients. Patients with ACS were randomly allocated to flowering plants (intervention) or no plants (control) in their room during index hospitalisation. Baseline data were collected. The primary outcome was the Hospital Anxiety and Depression Scale (HADS) depressive and anxiety symptom scores at discharge. Secondary outcomes were HADS depression and anxiety scores at 3 months. Both modified intention-to-treat (mITT) and per-protocol (PP) analysis were performed. 122 patients were included in the analysis after case exclusion, with all completing the HADS questionnaire at discharge and 89/122 (73%) patients completing the 3-month post-discharge HADS. At discharge, mean depressive symptom scores were lower in the intervention group, but only significantly so in the PP analysis (mITT 3.6/21 vs 4.6/21, p = 0.11; PP 3.5/21 vs 4.9/21, p = 0.04). There were no significant changes in between-group anxiety symptom scores (mITT 6.4/21 vs 6.1/21, p = 0.51; PP 3.3/21 vs 3.6/21, p = 0.67). The mean increase in depressive symptom scores at 3 months was smaller in the intervention group in both analyses (mITT 0.6 ± 3.6 vs 2.2 ± 2.6, p = 0.02; PP 0.8 ± 3.6 vs 2.4 ± 2.7, p = 0.03). Mean increase in anxiety symptom scores was not significantly different between groups (mITT 2.8/21 vs 2.5/21, p = 0.86; PP 3.3/21 vs 3.6/21, p = 0.67). Flowering plants during index hospitalisation for ACS reduced depressive symptoms in a per-protocol analysis but did not have a significant impact on anxiety symptoms. Increases in depression symptom scores were significantly smaller at 3 months post exposure to flowers compared to anxiety symptom scores.