The timepiece, located in Princes Street Gardens, was completed last week following more than a month of work by parks staff to plant over 35,000 individual flowers and plants.
The floral clock was first created in 1903 by the Edinburgh parks superintendent John McHattie. Each year it celebrates a different individual, organisation or anniversary. Past inspirations have included the Girl Guides Association, the 100th anniversary of Robert Louis Stevenson's death and the clock's own centenary.
The clock takes two gardeners five weeks to produce, and is trimmed, weeded and watered by one gardener for the rest of the season.
Plants vary each year but some of the more commonly used varieties include lobelia, pyrethrum, golden moss and succulents such as echeveria and sedum. It is timed to flower from July through until October.
It is 3.6m wide, with a circumference of 11m. The minute and hour hands measure approximately 2.4m and 1.5m respectively and when filled with plants, the large hand weighs around 36kg while the small weighs 22.7kg.
Until 1972 the clock was operated mechanically, and had to be wound daily. From 1973 it was electrically driven.
Neil Baxter, secretary of RIAS, said: "For many Scots, Edinburgh's floral clock is a very special childhood memory. Visits to the Capital were always sure to have the clock on the itinerary.
"This clock represents the very best of Scottish horticulture, just as the RIAS promotes excellence in our architecture. It is a tremendous honour that this year's clock marks the RIAS' centenary."
The Lord Provost, Donald Wilson, and environment convener Councillor Lesley Hinds, watched gardeners make the finishing touches.
Lord Wilson called the clock a "longstanding and popular addition to the city's summer attractions" and said it was as popular today as when it was first created in 1903.