I want to grow an annual flower that is good for cutting and also blooms in July or August for zone 3. I can start seedlings indoors. They would be transplanted to the garden end of May.
Zinnias Benary's Giant Blue Point Series
Perhaps the best cut flower I have ever met (and I have met a lot) is clary sage, or more specifically Salvia horminum. It's an annual which reseeds itself, and bears coloured bracts of deep pink, blue-violet or white with deeper colour striations. Plants will last at least one week in a vase (two weeks not unusual) and are easy to start, will grow almost anywhere. They perform beautifully in full sun and moist soil, but I have also grown them in varying degrees of shade and sunny, xeric conditions with excellent results. They usually begin flowering in June and will continue into about the third frost. Best flowering time is probably July-Sept. They are come and cut again plants.
Seeds available from Ontario Seed Company and William Dam.
Also consider larkspur. It's much easier to direct sow, but needs an early sowing to prosper (usually with the peas.) I have sometimes sown the seed on melting snow with good results.
Peak bloom is June through August. The more you cut, the better they bloom. They will go to seed if not picked or deadheaded.
Hope this helps.
Thanks for the ideas.