The Best Late-Summer Flowers For A Beautiful Garden

By August, a garden can start looking a little tired. It may be tempting to throw in the trowel. But that would be a shame with so many late-summer flowers just coming into bloom. All it takes is a little advance planning and some careful pruning, and you can maintain a gorgeous garden all the way until fall.

I know what I’m talking about, not only as a designer, but also as co-chair of a demo garden in Maryland that must be in peak flower in August for the County Fair. The garden is funded by the Master Gardener program and plays a key role in educating the public. The Fair falls at a time of year, however, that can be hard on flowers. Not only is it late in the season, but there are also wide swings in weather.

A view of our demo garden with the cow ‘show barn’ in the back

Indeed, in late July, I often lay awake at night worrying about how to keep the plants blooming. And this year, our garden encountered more challenges than usual. These included wild swings in temperature, a prolonged period of drought, and a 10-day deluge of rain. It was a perfect storm of horticultural disasters. 

It was a miracle then, that when we opened to the public yesterday, our garden looked better than ever.

Blanket Flower (Gaillardia) 

How did we do this? Upon reflection, I think our success hinged on four key elements:

CHOOSING LATE-SUMMER FLOWERS

If you want blooms in late summer, it helps to choose the right species. Following are the perennials that are in full flower today in our August garden, many of which started blooming in early July.

Other late-summer flowers like Japanese anemones, goldenrod, Joe Pye weed, physostegia (Obedient Plant), dahlias, zinnias and many plants in the aster family waited until mid month to begin blossoming.

But flowers alone are not often enough. We supplemented these perennials with dependable, late-flowering shrubs like abelias, ‘Annabelle’ and ‘Limelight’ hydrangeas and Knock-Out roses.

Hydrangea arborescens ‘Annabelle’

If you plant late-summer flowers in the right places (sun or shade, back or front of the border), you set the August/September garden up for success right from the start. It pays to educate yourself on what species bloom when and then design your garden around the seasons in which you most like to enjoy it.

PRUNING TO INCREASE OR DELAY BLOOMS

I’ve written a lot about the importance of deadheading and why it encourages a plant to produce more flowers. But there’s another secret to pruning. Early removal of blooms can not only cause a plant to bush out, but it can also delay flowering. Depending on what time of the season you make your cuts and by how much, you can coax your plants to flower later than they are naturally programmed to do.

Red hibiscus

My go-to reference for pruning is The Well-Tended Perennial Garden by Tracy DiSabato-Aust. I’ve used DiSabato’s techniques for years in my own gardens to get plants to flower later and longer. This in turn has helped our Master Gardener team create unique color combinations in our garden. And it’s helped ensure our plants are in peak flower at Fair-time.

New Dawn climbing rose with balloon flower in the background

Accordingly, starting in mid June, we hard prune many of our flowers, sometimes removing as much as a third of the plant. This encourages the plant to branch out instead of becoming leggy. And, if we get our timing right, the flowers are delayed until the beginning of August, or just in time for the Fair.

Here are two examples:

DAYLILIES

In addition to snapping off dead blooms, we make sure to immediately remove any seed heads that start to develop. In the plant world, once the seedpods appear, the plant thinks it’s done for the season and stops flowering.

Removing spent blooms as often as possible will prolong daylily flowering

But by diligently removing the dead flowers and pods (as well as cutting all spent stalks down to the ground), the plant gets the message to keep on blooming. Using this technique, we’ve kept some of our daylilies blooming for a week or two longer than they usually do.

ECHINACEAS

These sturdy flowers start blooming in our garden in July but get leggy by August without some prudent intervention. To keep them flowering, we continuously remove spent blooms, making our cuts down along the stem where we see the newest flower just starting to develop.

Echinacea purpurea, sneezeweed and salvia ‘Victory Blue’

By continuous pruning, we keep our coneflowers thick and blooming pretty much until the end of summer.

PROPER IRRIGATION BOOSTS LATE-SUMMER FLOWERS

At the demo garden, we use a drip system of irrigation. It works relatively well until someone at the fairgrounds decides to turn off the main water source. This year we installed a timer and spoke with the staff to coordinate. Still, there were many times, especially with new plantings, that we needed to ask our team to hand water.

Purple physostegia and artemisia ‘Powis Castle’ make a great combination

Although it seems obvious, I cannot emphasize enough the need to water. Drip irrigation alone is rarely sufficient in hot climates to get new plants to establish properly. We always supplement our drip system with hand watering during dry spells, making sure to water long and deep. Deep root watering is always better than a short surface spritz, which only teases the roots before quickly evaporating.

ANNUALS AND BULBS MAKE GREAT LATE-SUMMER FLOWERS

Finally, nothing beats zinnias and dahlias for dependable late-summer flowers. Zinnias come into their own by late August and my own dahlias at home keep flowering until well into October. It’s a great pick-me-up to see all these happy, bright flowers appear suddenly at the end of the season.

Zinnia mix in the late summer garden

We plant our (potted) zinnias in the garden in July and prune them down as they grow. This encourages them to thicken up before blooming. The dahlias go in the ground in June. And both will continue to brighten our demo garden until long after the Fair has ended.

Looking for late-season annuals you can grow from seed? Check out ButterBee Farm’s top recommendations for the cutting garden. 

 

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About carole funger

I'm a garden designer and Maryland Master Gardener living in the Washington, DC area. I blog about new trends in horticulture, inspiring gardens to visit and the latest tips and ideas for how to nurture your own beautiful garden. Every garden tells a story. What's yours?

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