What is the best fertiliser for roses to promote bigger blooms?

rose fanciers that show their prize roses don't feed to get bigger blooms, they select a bud and remove all the others.... so the plant has only the one flower to push..... but that only works with roses that have large-ish blooms to start with...... nothing you can do would make a Lady Banks rose bloom larger!!.... the best you can do is feed with a bloom booster fertilizer where the middle number is largest, like 10-20-10..... keep it happy with full sun, great air flow, in a slightly acidic soil, use compost and mulch and make sure it is watered to its needs and draining well.... if it's happy, it makes nice flowers.....