Clematis 'Zo23020' (GLORIOUS DAY) belongs to the Viticella group and blooms from July to September. The flowers are about 6 to 8 cm in diameter and are dark violet in color. The plant can reach a height of about 300 cm. GLORIOUS DAY is moderately winter-hardy (zone 6) and is best pruned in March to a height of about 25 cm. This Clematis was bred by J. van Zoest Beheer BV from Boskoop. Plant breeder's rights have been applied for. The plant will be available on the market from August 2023 through J. van Zoest BV, which has also submitted the plant for novelty evaluation.