One other way is to buy large-ish plug plants of something you fancy and plant them out. Cosmos are readily available and make excellent cut flowers, for example
This year we have a range of dahlias (an increasing range every year it seems) verbena bonariensis, alchemilla, zinnias, roses, delphiniums, hardy fuchsias, large white daisies, crocosmias of various colours, pansies, alstromeria, lavender,alliums, irises, spring flowers from bulbs, plus primroses and violets, and from seed: cosmos, zinnias, tangerine tagetes, cerinthe, bupleurum, calendula, sweet William (biennial), small flowered begonias. Flowering shrubs are useful too.
Hope that gives you a few ideas. I am sure people will have many more to add to the list (as Sragh raven does of course
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