The party, hosted by the Roof Gardens in London, was held exactly 175 years after the Gardeners' Benevolent Institution was formed by landowners as a pension fund for their head gardeners. The charity's patron HRH Princess Alexandra joined Titchmarsh, its president and guests from the horticulture industry at the event.
Pledging an undisclosed sum to the charity, Titchmarsh said: "Today I want to demonstrate that gardeners are different in another way. They put their money where their spade is. I ask you all to make your pledge today to do your bit for your profession - and those of you who are supporters to do the same."
He added: "Gardeners can be struck down with terminal illness, the incapacity of close relatives, the loss of mobility, disability, depression, poverty and homelessness. These are tragedies that affect people in all walks of life but those on the lowest of incomes are more deeply affected than most."
To mark its anniversary, Perennial is asking people to try to raise £175 each for its 175th year.