The Best Late-Summer Flowers For Your August/September Garden

In mid August, it’s sometimes hard not to look at your garden and throw in the towel. By that, I mean take out the pruners and cut down all the moldy, dried out stems or simply turn a blind eye to the whole debacle. But that would be a shame with so many late-summer flowers just now coming into their own. It just takes a little advance planning and some careful pruning and you can have a garden that keeps flowering all the way until fall.

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

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

Come late July, I often lay awake at night wondering just how the garden will remain in flower. And this year, our demo garden endured more challenges than usual, including extremes in temperature, a prolonged period of drought and a 10-day deluge of rain. Additionally, a cold spring led us to plant later than usual (every year we add or replace some flowers) only to watch the the temperatures soar 20 degrees above normal the following day. It was a perfect storm of garden-related disasters that made us all wonder what would possibly be left for the Fair.

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

Blanket Flower (Gaillardia) is a member of the sunflower family

How did we do it? Upon reflection, I think our success hinged on four important things: 1) Choosing late-summer flowers; 2) Diligent pruning to increase or delay blooms; 3) Proper irrigation; and 4) Planting annuals and bulbs to fill out bare spaces.

CHOOSING LATE-SUMMER FLOWERS

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, dahlias, zinnias and many plants in the aster family waited until August to begin putting on a show.

We supplemented these flowers with such dependable late-flowering shrubs as abelia, hydrangeas ‘Annabelle’ and ‘Limelight’ and Knock-Out Rose.

Hydrangea arborescens ‘Annabelle’

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

PRUNING TO INCREASE OR DELAY BLOOMS

I’ve written a lot previously about the importance of deadheading and why it encourages a plant to produce more flowers. But there’s another secret to pruning: judicious and early removal of blooms can also cause a plant to bush out and most importantly, it can delay flowering. Depending on what time of the season you make your cuts and by how much, you can coax plants to bloom at times later than they are naturally programmed to do.

Red hibiscus

My go-to reference for all types of pruning is The Well-Tended Perennial Garden by Tracy DiSabato-Aust. I’ve used it for years to get plants to bloom longer and at times they aren’t accustomed to. This in turn has helped our Master Gardener team create unique color combinations in our demo garden and orchestrate things so that our plants are in peak flower come Fair-time.

New Dawn climbing rose with balloon flower in the background

Starting in mid June, we hard prune many of our flowers, lopping off sometimes as much as a third of the plant. This encourages the plant to bush 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 the daily dead blooms (daylilies are called daylilies for a reason), we make sure to immediately remove any of the bulbous seed heads that start to develop. In the plant world, once the seedpods start to develop, the plant thinks it’s done for the season and stops flowering.

Removing spent blooms as often as possible will prolong daylily flowering

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 twice as long as they usually do.

Echinaceas. These sturdy flowers start blooming in our garden in July but can get long and leggy by August without some prudent intervention. We continuously remove the flowers as soon as they start to dry out, making our cuts down along the stem where we see the newest flower just starting to develop.

Echinacea purpurea, sneezweed and salvia ‘Victory Blue’

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

PROPER IRRIGATION

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 fairgrounds staff to get everyone on the same page. Still, there were many times, especially with new plantings, that we needed to call on 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.

THE IMPORTANCE OF ANNUALS AND BULBS

Finally, nothing beats zinnias and dahlias for filling in bare spaces in the late summer garden. 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 to encourage them to thicken up before blooming. The dahlias go in the ground in June. And both will be continuing to brighten our demo garden well after the Fair has ended.

 

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