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The sudden heat and humidity of summer has gardeners dancing a seasonal salsa

The mophead hydrangea signals a transition to a more challenging moment in the garden’s year. (Adrian Higgins/The Washington Post)
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The hydrangeas that came through the late spring frost unscathed are beginning to bloom. For many folks, hydrangeas are as timeless and carefree as summer itself. Big, blue or pink mopheads evoke notions of vacation at the beach, the whiff of sun lotion and the dulcet beat of crashing waves.

That’s the ideal, and it may still hold true in more northern, cooler climes. In the Mid-Atlantic, though, the summer garden is a far more complicated affair. This is because the climate shifts abruptly in June from something temperate to one far more tropical in its heat, humidity and unwillingness to cool off much at night. It might be that last aspect that is so trying for plant and gardener alike.

This climatic dichotomy presents real challenges, because our permanent plantings of hardy plants — including hydrangeas — are driven by their tolerance for winter cold, not summer heat.

One effect of this is that plants that are quintessential summer bloomers in other regions are compressed into our uneasy June zone between spring and summer. I’m thinking of roses, clematis, lavender and, yes, hydrangeas.

For that reason, I view the flowering of the hydrangeas more as signaling the end of spring than the beginning of summer, even if the faded flower heads remain decorative for months.

An uplifting model for something we could all use: Refuge

This is not to say that the Washington summer is a bust — some people actually like the clinging heat, though I doubt they are the ones toiling outside in the midafternoon.

And I shouldn’t be so petulant; the warmth here produces the kind of vigorous growth that gardeners in other places can only dream about. European visitors swoon with desire and disbelief at the sight of the hyacinth bean, a purple-leafed vine resplendent in August with striking purple stems, flowers and seedpods. This would be a feeble thing in the grand palace gardens of France, but in my lowly vegetable garden, it appears automatically from the warming earth and grows quickly.

There are places where tomatoes and peppers must be raised in little home greenhouses. Here, we scramble for a stake or cage large enough to tame the monsters.

So we deal with this heat and humidity. Perhaps the best way to tackle it is to plant a shade tree and wait 20 years, but where’s the instant gratification in that?

As summers seem to have become longer and hotter, gardeners have turned more to using tropical plants so that by midsummer, the deck or patio resembles a dreamy jungle of banana “trees,” cannas, coleus and other leafy exotica.

What was once just something we called elephant ears is now a high-falutin cultivar of alocasia or colocasia, truly stunning in size, leaf venation and sheer presence. I have never grown tired of the Abyssinian banana with its red-tinged stems and leaves.

The greater challenge is to find hardy plants that will handle the next few weeks, and this takes some homework. Black-eyed Susans, Russian sage and purple coneflowers are agreeable stalwarts, but they benefit from more inventive company. I used to like adding towering, fragrant and big-bloomed longiflorum lilies to the mix, if only because I find many of the Asiatic lilies so stiff and garish. But there are other, more natural-looking lilies worth trying, including the Citronella lily, the variety Casa Blanca and Lilium leichtlinii, found in orange or yellow forms. Alone, they are spindly, but interplanted with other perennials, they add a real floral punch.

If you are drawn to native plants, the blazing star of the American grassland deserves greater use in our gardens. Its purple flowers, born on long stems, arise from feathery clumps. The common version is Liatris spicata, which blooms now, but others vary by size, flowering period and the structure of their blossoms (although all share a family resemblance). The species L. squarrosa is a shorter plant with larger flowers, and blooms later. L. microcephala has a profusion of smaller flower spikes emerging from handsome, fine-textured clumps. L. aspera flowers in late summer into fall.

Thistlelike eryngiums help to carry the garden through the season; who could resist one named Miss Willmott’s ghost (Eryngium giganteum), after a gardener who surreptitiously scattered seeds in friends’ gardens, or the native prairie plant known as rattlesnake master (E. yuccifolium)? The latter will take drier soils than the former.

I like large perennials in the hot summer. There is something defiant about them. In early summer, that might be the Rudbeckia maxima, and later, the New York ironweed (Vernonia noveboracensis). For decades, Joe Pye weed has been an extremely valuable shrublike perennial for the summer garden, because it adds structural mass, and its purple-domed flowers are powerful magnets for pollinators. The challenge is to keep a stand from splaying by August. This is achieved by cutting it back by about a half in June to promote a bushier regrowth, or by picking one of the more relatively compact varieties, such as Gateway and Purple Bush.

Most asters are for September and October, but the flat-topped white aster, which grows to about two feet, is a summer bloomer.

The truly redeeming players in the summer garden are ornamental grasses. I have moved away from the massive miscanthus grass, not only for its invasiveness but also because it lacks the elegance of grasses such as switch grass, molinia, prairie dropseed and little bluestem.

The real value of these grasses is their promise of the best period of the year, which lies beyond the dog days. From late August to early November, the so-called Fifth Season offers the deep satisfaction of mellow decline, when the herbaceous garden is replete, the sun is lower and kinder, and the nights are cooler.

Marking this more-welcome transition will be, well, the hydrangea. Not the varieties now in flower (of Hydrangea macrophylla and serrata), but the lingering flower heads of Annabelle types and, more imposingly, of the shrubby panicle hydrangea. Grandiflora is the classic and hulking variety, but others have been developed for a more refined habit and attractive flower panicles. Limelight is one, valued for its greenish tinge. Phantom has strikingly large white panicles on a compact bush. For the full autumn effect, the one to plant is Tardiva, which arrives late to the party but then stops the guests from leaving.

@adrian_higgins on Twitter

Tip of the Week

Find a sunny corner of the garden to sow sunflower seeds. Short, multibranched varieties are perfect for cutting, or filling holes in the summer border. Tall, single-stemmed varieties make a statement while providing food for pollinators and birds.

— Adrian Higgins

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