Smokers are ignoring attempts to ban tobacco use from the Royal Cornwall Hospital site in Truro.
The hospital said the problem was highlighted by smokers stubbing out their cigarette ends in a new floral display.
The flower display had been planted at the entrance to the hospital to celebrate the Phoenix Stroke Appeal reaching the final stage of fundraising.
The hospital said grounds staff have had to spend time cleaning up cigarette butts when they should be concentrating on tending the plants and shrubs on the site.
The Royal Cornwall Hospital Trust (RCHT) sites have been supposed to be smoke-free since 2007 but hard-core smokers ignore the rules.
Greg Smith from the estates team at RCHT said: "It is demoralising for those who have given up their own time to help make our hospital entrances more welcoming to see their work spoilt in this way.
"If the plants get a chance to thrive our hope was to see a colourful display for the summer."
This Friday is World No Tobacco Day and throughout this week RCHT is making a plea to everyone to help discourage anyone smoking on the hospital sites by asking them to put out their cigarettes.
The Estates Team is also looking for local businesses or individuals who would be willing to sponsor more troughs and planters for the hospital entrances. For more information email gregory.smith@rcht.cornwall.nhs.uk.
