Clematis flower seed takes about 21 - 28 days to germinate. You can sow the flower seeds in trays indoors and transplant the seedlings after frost season, or sow the flower seeds directly outside after the danger of frost has passed.
Before sowing Clematis seed, refrigerate the seed for 2 - 3 weeks. Some gardeners prefer to start the flower seed outdoors in the late fall or in the winter in a cold frame. The cold helps to break the dormancy.