What's Blooming in August: Zone-by-Zone Guide

August is a turning point. The garden does not look like June anymore, and it should not. Some plants are spent. Others are just getting started. The gardeners who planned for this transition are the ones with borders that still look alive right now. If your garden has an August slump, take notes. You can fix it. But first, here is everything that is blooming this month.

Zones 3-5: Every bloom counts

August in cold zones has a bittersweet edge. The garden is still full, but you can feel fall approaching. First frost could arrive in September, so every bloom matters. This is the time to appreciate what is still going and to notice what is just beginning.

Coneflower and black-eyed Susan are still the workhorses, blooming reliably through the month. Do not deadhead all of them. Leave some spent flower heads for the goldfinches, which start feeding on the seeds in late August. Garden phlox keeps blooming in dense, fragrant clusters. Cut spent stems to the base and side shoots will keep producing flowers.

Joe-Pye weed is finishing its spectacular run. Those enormous mauve-pink domes look stunning against the late summer sky and are covered in butterflies making the most of the season. Hostas are sending up their flower spikes now. People grow hostas for the foliage, but those lavender or white bell flowers are genuinely pretty and worth noticing.

Here is the exciting part: asters are starting. Early varieties begin opening in late August, and they will carry the garden straight through October in these zones. Sedum flower heads are fattening up and beginning to turn pink. Goldenrod is just starting to show color. These three plants together are the foundation of a great fall garden in cold zones.

Zones 6-7: Managing the transition

August in zones 6 and 7 is where you see the gap between gardens that were planned for continuous bloom and gardens that were not. A lot of the early and midsummer perennials are winding down. The smart move is to lean into the plants that peak right now.

Dahlias are the August headliners. From dinner-plate sized blooms to tight pompons, from deep burgundy to bright coral, dahlias hit their absolute peak this month. If you are not growing dahlias, August is the month that will convince you to start. They are extraordinary cut flowers too. Pick them in the morning and they last a week in a vase.

Russian sage is in full bloom, its silvery stems and lavender-blue flowers creating a haze of color that holds up beautifully in the heat. Butterfly bush is still loaded with flowers and covered in swallowtails. Cardinal flower is blazing scarlet in moist, shady spots.

Japanese anemone starts blooming in late August, and it is one of the most elegant flowers in the garden. Simple pink or white blooms on tall, wiry stems that sway in the slightest breeze. It bridges the gap between summer and fall perfectly. Toad lily begins opening its exotic, orchid-like spotted flowers in shady spots. Both of these plants solve the late-summer shade problem that frustrates so many gardeners.

Zinnias are still going hard. Cosmos looks better in August than it did in July, taller and more floriferous. Sunflowers are at their peak, turning entire gardens into something cheerful and generous. Knock Out roses are on their second or third flush, proving again why they are the most reliable flowering shrub in American gardens.

Zones 8-10: The heat finally breaks

August in warm zones is when you can start to see the end of the worst heat. Not yet, but soon. The garden has been grinding through summer, and the tough plants that made it this far deserve respect.

Crape myrtle is still blooming magnificently. It will keep going into September. Lantana has not slowed down at all and will not until frost. Salvia keeps its intense blue spikes going. Blanket flower is still producing its fiery pinwheels without any extra water or attention.

Zinnias planted in succession are providing the best cut flowers of the year. Cosmos self-sows freely in warm zones, so you may have volunteer plants blooming in spots you did not expect. Dahlias perform well in zones 8-9 with afternoon shade and consistent moisture. In zone 10, they struggle unless you have a cooler microclimate.

The big news in warm-zone August is that fall planting season is approaching. Start making your lists now. Perennials, shrubs, and trees planted in October and November will establish roots through the mild winter and hit the ground running next spring.

What to do in August

Order spring-blooming bulbs now. Tulips, daffodils, crocuses, and alliums sell out fast, and you want first pick. They will not go in the ground until fall, but ordering early guarantees you get what you want.

Plant asters and sedums now if you do not already have them. They are available at every nursery this time of year, often already in bloom, and they will establish quickly in the warm soil. This is the fastest way to fix an August slump for next year.

Keep deadheading dahlias, zinnias, and cosmos. The more you cut, the more they bloom. Give roses a light feeding to push that fall flush. In cold zones, stop fertilizing perennials and shrubs by mid-August so they can start hardening off for winter.

August is the best month to evaluate your garden honestly. What peaked? What flopped? Where are the gaps? Take photos now and compare them to your June and July garden. The differences will tell you exactly what to add this fall. Browse our Nonstop Color collection for plants that bridge the summer-to-fall gap, or explore the Fragrant Flowers collection for plants that make late summer evenings memorable.

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