More than 10,000 individual rose bushes bloom in the International Rose Test Garden (IRTG) from late May through October, representing over 610 different rose varieties. The majority of roses in the Garden are commercially available. About 10 to 20 varieties are replaced each year with some of the best new roses released onto the market. Roses bloom from late May to October depending on the weather.

The primary purpose of the Garden is to serve as a testing ground for new rose varieties. In the beginning, while World War I was raging, hybridists sent roses from around the world to Portland’s garden for testing.