Here are some of the blue and purple flowers still blooming in October in zone 3. These are the hardier perennials that have a long flowering time and can still produce colour as most other perennials are fading away for the year. If you’re viewing on a lower resolution, you need to click the picture to see the overflow.
On the top left are the flowers of Geranium ‘Rozanne’ (cranesbill) with five rounded petals, each with a white centre. These have been in bloom since July. ‘Rozanne’ is a terrific plant for a long season of pretty blue flowers. The foliage still looks fresh, too. It is such an easy care perennial, and goes well with many other plants. I like to use them for underplantng shrubs or tall perennials, as they doesn’t mind the shade they make. You can see more pictures of how these hardy geraniums look under a lilac here.
On the upper right of the photo is Phlox paniculata ‘David’s Lavender’ (tall garden phlox), which has soft lavender coloured petals, each with a smaller white bee in the middle than ‘Rozanne’. Mine start flowering at the end of August in zone 3, and continue through until October. They put on a good show, even in part shade. You can see that the white ‘David’ behind finishes a little earlier than the purple flowers.
Campanula poscharskyana (Carpathian bellflower) is on the lower left, with some unopened buds still. These blooms are a pretty lavender blue., and have five narrow petals in a star shape. Many of the plants still have a good number of flowers, but in summer there can be over a hundred blooms on one small 30 cm square (1 foot square) plant. They produce well in the shade. The starry blooms are arranged along long flowering stems that mostly spread out along the ground. This bellflower goes from July until very late Fall. It is another perennial that is very useful for underplanting shrubs or tall perennials with a narrow base. There are more pictures of using this Campanula for underplanting in this article.
Campanula rotundifolia (harebell or bluebell of Scotland) is shown on the bottom right side of the collage. These perennials have been blooming since June, and are still producing many blue flowers, even after the first frost. The flowering stems are about 30 cm tall (1 foot), or a little taller, with many bells arranged all around the stems. There are more photos of Campanula rotundifolia in this post from last year. Another bellflower still blooming is Campanula cochlearifolia (fairy thimble bellflower). The blooms are smaller versions of C. rotundifolia on shorter plants. Both of these Campanula put on a good display in part shade.
You can see from the pictures, that the maple tree has lost all of its leaves, and perennials like lily of the valley have faded to yellow, but some hardy perennials continue to bloom through late Fall. Those two Campanula often flower right through October and sometimes up until December, or the first snowfall which usually comes first. These are all great plants for keeping the garden going in soft shades of blue and lavender, when other perennials are starting to sleep.