No mater how much work we put into our roses to sustain bloom all through the season, and not matter how successful we are with that endeavor, the first spring bloom is always the best. Some roses continue to bloom in floriferous phases afterward, while others bloom sporadically but continually; but there is nothing like the first bloom phase. The last blooms are just waiting for autumn.
Of course, concentrating resources into early bloom is very sensible. That is why so many plants bloom only once in spring. It gives them time to get pollinated, develop seed and fruit structures, and finally disperse their seed or fruit structures, all before winter. Plants that bloom in summer or autumn are either from regions where winters are not too harsh, or where summers are harsher.
Because summer weather in most regions tends to be warmer and drier than spring weather, flowers that prefer to bloom in summer tend to be more prolific but smaller and less colorful. By this time of year, they are more reliant on wind for pollination rather than insects anyway. Therefore, they do not need to be big and colorful to attract pollinators, although some are fragrant just in case.
Sunflower, blanket flower, cone flower, zinnia, cosmos, delphinium, dahlia and of course rose, are some of the favorite flowers in the garden as well as for cutting in late summer and into autumn. Cut dahlia flowers should get their water changed daily so that they do not rot and smell bad so soon. Canna blooms about now, but does not last so well as cut flowers. Lily-of-the-Nile is finished.
Believe it or not, lemon bottlebrush is a delightful cut flower for those who are not allergic to it or repelled by the aromatic foliage. So are some of the showier eucalyptus, such as the red flowering gum, Eucalyptus ficifolia. Mexican blue sage that was cut back to the ground over winter blooms a bit in spring, takes a bit of time off through summer, and then starts to bloom as summer ends, ultimately blooming spectacularly early in autumn. A few other sages bloom as late, but few are good for cutting.