The Queen has granted a royal charter to the IoH that will come into legal effect when it is sealed by the Crown Office at the House of Lords in the new year.
IoH president Leigh Morris said: "What a fantastic landmark moment for the institute, its members, officers and for all horticulturists in the UK and Ireland.
"Chartership should give our members a higher status, stimulate more to join us and give the IoH much greater gravitas in our advocacy for the industry."
He added: "I hope to see many more designers, landscapers, groundsmen, nursery propagators, greenkeepers, commercial growers and professional gardeners joining us.
"The granting of the royal charter to the institute has undoubtedly raised the bar for professional horticulture in the UK and Ireland and exciting times lie ahead."