The objectives of this study were to examine the effects of a horticultural activity program on the emotional intelligence, prosocial behavior, and scientific investigation abilities and attitudes of kindergarteners. A total of 336 children aged 5 to 7 years in public and private kindergartens and day care centers in Incheon, South Korea, participated in a 24-session horticultural activity program. This program included indoor and outdoor activities such as planting seeds, transplanting plants, making and applying eco-friendly fertilizer, watering, harvesting, using plants to make crafts, and cooking with produce. It was designed to improve the emotional intelligence, prosocial behavior, and scientific investigation abilities and attitudes of kindergarteners. Each session lasted an average of 50 minutes and was held once per week. The results of the study showed that the 24-session horticultural activity program improved the emotional intelligence, prosocial behavior, and scientific investigation abilities and attitudes of the children (P < 0.05). Satisfaction with the program was very high among both the children and their teachers and parents. Future studies should consider exploring the effects of horticultural activity programs on children in different age groups.