'Radpastel' originated from a hybrid cross conducted by the breeder in July 2002 in Greenfield, Wisconsin, USA. The hybrid cross was made between the variety 'Radquid', as the female parent, and the variety 'Radcor', as the the male parent. The final selection of 'Radpastel' was made in January 2013 based on its yellow flowers, bushy, rounded growth habit, attractive foliage and resistance to black spot, powdery mildew and rust.

The female parent (i.e., seed parent) was the ‘Radquid’ variety (non-patented in the United States), and the male parent (i.e., pollen parent) was the ‘Radcor’ variety (U.S. Plant Pat. No. 17,346).