Network Rail said it hopes the installation will "lift people's spirits" during their journeys.
The Brighter Journeys initiative aims to raise awareness of the free Hub of Hope app, which helps users access support if they are struggling with mental health.
The flowers will initially go on display at London Liverpool Street station between today (May 9) and Wednesday (May 11) to mark Mental Health Awareness Week.
The installation will then be moved to Leeds City Station as well as Edinburgh Waverley, Birmingham New Street, Stevenage, East Croydon and Cardiff.
A survey of 5,136 UK adults by the British Association for Counselling and Psychotherapy indicated that 70% of people say their mental health has been negatively impacted by the coronavirus pandemic.
Nearly a fifth of respondents (19 per cent) described their mental health as "poor".
Brighter Journeys is a joint campaign between the rail industry and mental health charity Chasing the Stigma.
Rupert Lown, chief health and safety officer at Network Rail, said: "We recognise that life since the pandemic is difficult for many people, with many challenges yet to be overcome.
"We hope that by running this campaign, we are bringing happiness and cheer to many passengers as they go about their daily lives, reminding them to take a pause and have a moment to connect with nature."
Jake Mills, founder of Chasing the Stigma and Hub of Hope, said: "Nature is really important for mental health, so we hope commuters enjoy seeing these floral installations and they put a smile on people's faces.
"We also hope that this acts as a reminder that no-one is ever alone, and mental health support is available at any time.
"You don't have to be in crisis to get help. If anyone is struggling or knows someone who needs help, please download the Hub of Hope app."