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Allan designs and plants flowering gardens in Montreal, Zone 5 [USDA Zone 4] .

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Late Blooming Perennials

Some of my garden blogging friends who live in hot growing zones, report that their perennial flowers are spent by July due to the brutal heat of summer. I have had a different challenge. Historically, July was the month when I would leave town for vacation. Planning a late summer garden did not seem to be that important if there was no one at home to appreciate or tend to it. However, upon my return in August, I would be greeted by desolate flowerbeds and that was disappointing. This depressing situation became my inspiration to plan a colorful garden for late summer.

August in Canadian Zone 5 or US Zone 4 can be temperate. The days are usually hot and evenings are comfortable, sometimes cool. Flowers bloom nicely throughout the month; many will even flourish in September. With some planning, gardeners in this growing zone can have very colorful and interesting flowerbeds to finish off the season. Here are some of the perennials that I grow in August and September. I am certain that there are more than I have listed here. These are the old faithfuls that have worked for me.

Blue flowers for Late Summer:- Agastache, Campanula Samantha, Campanula porscharskyana, Campanula portenschlagiana, Clematis, Geranium Rozanne, Nepeta, Perovskia, Phlox paniculata , Platycodon, Scabiosa, Salvia, Verbena hastate, Veronica.

Pink flowers for Late Summer:- Aster Alma Potchke, Astilbe chinensis pumila, Astilbe taqueta superba, Clematis, Chrysanthemum  rubelum X Clara Curtis, Chelone oblique, Dianthus Deltoids and gratianopolitanis, Eupatorium, Geranium Sweet Heidi, Geranium Orkney Cherry, Geranium Max Frei, Phliox paniculata, Vernonia.

Hot Colored flowers for Late Summer:- Coreopsis, Echinacea, Gaillardia, Helenium, late blooming Hemerocallis, Knautia, Kniphofia, Papaver nudicale, Phlox paniculata, Sedum.

Flowering Shrubs for late summer:- Rainbow Knock Out Rose, Knock Out Rose, Rose Carefree Wonder, Rose Bonica, Hydrangea.

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Reader Comments (4)


This couldn't have come at a better time. My garden might look great for a couple of months, but by this time of year, it’s pretty ragged. My Jacob Cline bee balm and hyssop is doing well, along with my knockout roses, cannas, snapdragons, penstemon and a few other things, but we've gotten so much rain that I haven't been deadheading as much as I normally would, and now that it's finally dried out a bit, everything is going to seed. That along with the gaping empty hole leftover after the oriental poppies die back has left it pretty pathetic. I love the look of the knautia, a fun new plant to try for next year.

August 6, 2010 | Unregistered CommenterLisa

Allan, I agree with all of these. I also have Euputorium Chocolate and Boltonia. There are also many late daylilies which I am just learning about.


August 6, 2010 | Unregistered CommenterEileen

My quest has always been for blooms for absolutely as long as possible. Sure, the Spring and early Summer rush is always spectacular and well worth planting heavily, but there are other months of the year. I began really supporting later-blooming things, the more I thought about it - the Coreopsis, Campanula's, Black Eyed Susan's all made the list. And I also began planting the heck out of Rose of Sharon - in all the bloom colors. Late-blooming things are very under rated in our rush to "Bloom Up".

August 9, 2010 | Unregistered CommenterSteve

Wow! Great tips and informative post for all landscape designers

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