The multi-billion dollar ornamental plant trade benefits economies worldwide but shifting and more streamlined globalised supply chains have exacerbated complex environmental, sustainability, and biosecurity risks. We review environmental and social costs of this international legal trade, and complement this with analyses of illegal plant trade seizures and plant contaminant interception data from the Netherlands and the UK. We show global increases in ornamental plant trade, with notable supply expansions in East Africa and South America and issues including biodiversity loss, aquifer depletion, pollution, and undermining of access-and-benefit-sharing and food security. Despite risk mitigation, interception data showed considerable volumes of contaminants in ornamental plant shipments, yet taxonomic identification was not always possible, highlighting uncertainties in assessing biosecurity risks. With high-volume and fast-moving transit of ornamental plants around the world, it is essential that standards are improved, and data on specific risks from trade are collected and shared to allow for mitigation.