How to Fertilize clematis 'Sunset'?
High-potassium blooming fertilizer every three weeks pre-bloom season

clematis 'Sunset' · Clematis 'Sunset'
Plant in a moisture-retentive, well-drained soil, with the roots and base of the plant kept cool and shaded by other plants or a layer of pebbles at the base. Plant with the crown 5-8cm (2-3in) deep to encourage new shoots to grow from below ground level. Can be grown in containers at least 45cm (18in) deep and wide in a soil based potting compost. See clematis cultivation for more advice
High-potassium blooming fertilizer every three weeks pre-bloom season