These 6 Classic Plants Aren't Standing Up to Modern Heat Waves – Here's What to Plant Instead
Heat waves are cooking traditional garden favorites. Here are the classic plants that fail in the heat and the tough, beautiful swaps to plant instead.
“Here comes the sun,” goes the classic Beatles song. “Here comes the sun, and I say, ‘It’s all right.’” But some 60 years later, the summer sun is not always a sign of hope, and it can cause issues in the garden.
I just got back to San Francisco after some months in France. April and May were a delight but late June and early July brought a heat wave – with the highest temperatures ever recorded in the country (think 107 degrees F).
These temperatures killed off some of my favorite garden shrubs and made me rethink what to plant in the future. Let’s take stock of some traditional garden plants that struggle (or give up the ghost) in extreme heat as well as some great, heat-tolerant replacements.
1. Hydrangea (Hydrangea spp.)
I have never seen my hydrangeas looking better than they did in April and May. I have three bigleafs, (Hydrangea macrophylla) two mopheads and one lacecap variety. They were stunning in spring, totally covered with the huge flowers, and even the leaves were starting to look baked.
Hydrangeas generally prefer morning sun and afternoon shade, so I have all of my plants planted where they don’t get much direct afternoon sun, but that did not save them. After one week of 100-plus temperatures, the pink and blue flowers had turned brown or green and when I left, they were beginning to drop.
Plant instead: Pentas (Pentas lanceolata)
We’ve found the perfect, heat-proof alternative. Pentas love intense sunshine and thrive in high heat. That’s why they are so popular in Florida. And they look a bit like hydrangeas with their blossom clusters. Their star-shaped flowers are a target for hummingbirds and butterflies.
2. Peonies (Paeonia spp.)
With large, fragrant, long-flowering blooms, peonies are one of those shrubs that grace many a garden. These classic flowers need a site with mucho sunshine - at least 6 hours a day! But that doesn’t mean they will thrive in heatwaves.
The type of intense, direct hot sunshine we saw this summer does not make a peony happy. I saw my peony leaves scorch in two days, and the third day, the gorgeous petals began to fade and wilt. It’s enough to make a grown gardener weep!
Plant instead: Heat Tolerant Roses (Rosa spp.)
Most rose plants need some direct sun, but only a few, heat-tolerant roses survive temperatures of 100 degrees F for more than a few minutes. The ones that do share these traits: thick, leathery foliage; lots and lots of petals; and their own roots rather than grafted roots.
We recommend "Belinda’s Dream," said to be the top pick for the Deep South. Its huge pink flowers are intensely fragrant and don’t blink in 100-degree weather. "Julia Child" comes in next, with its continuous clusters of buttery yellow, licorice-scented blooms, even when summer heat hits news highs. Roses in the "Knock Out" family are also amazingly heat resistant. heat, their blooms may temporarily shrink or fade.
3. Astilbe (Astilbe spp.)
Many of us have astilbes in the garden since they are known to be one of the easiest perennial flowers to grow. Their flowers are unusual as well, plume-like blooms in soft shades of white, pink, purple, and red. They rise above the airy foliage on stiff stocks. I can tell you from personal knowledge that these are extremely low maintenance additions to the shade garden, requiring only moisture and damp, loamy soil.
All these positive features are negatives as the summer temperatures rise. As summers turn hotter and drier, the feathery foliage actually burns - look for brown, crispy edges on the leaves - and wilting, browning blossoms. The plants just can’t uptake water fast enough to keep its flowers looking good.
Plant instead: Russian Sage (Salvia yangii)
With its soft but dramatic spikes of lavender flowers lasting for up to four months, Russian sage offers the same type of unusual eye candy to the garden that makes astilbe stand out. But as summers swelter, Russian sage just keeps getting prettier while astilbe just cooks. Don’t even think of planting this salvia in shade! It will cause the stems to become weak, lax, and prone to flopping.
4. Bleeding Heart (Lamprocapnos spectabilis)
Old-fashioned bleeding heart is both stunning and darling, with its unique, dangling heart-shaped flowers and finely divided foliage. It just makes you happy to see it in the garden - and that’s why it is so popular with gardeners.
But a bleeding heart plant needs shade - partial to full - and also moist soil. They work well in woodland settings and require consistent moisture and full protection from hot afternoon sun. Obviously, sizzling summer temperatures will not do any favors for these favorites. They won’t survive anything hotter than 75 degrees F.
Plant instead: Foamy Bells (Heucherella spp.)
Heucherella is a plant that does double duty. It displays fabulous foliage as well as darling little blossoms. Known as foamy bells, this perennial is a hybrid of Heuchera (coral bells) and Tiarella (foamflower), carrying the best traits of both. Like Heuchera, the leaves come in a wild variety of colors, sometimes streaked with intricate veining. Like its other parent foamflower, Heucherella grows tall stems with delicate frothy flowers on tall stems that dance in a gentle breeze.
Plant Heucherella foamy bells in filtered, dappled shade. Once installed, they tolerate heat and humidity, thriving in southern regions. If you choose Heucherella (foamy bells) varieties with Heuchera villosa parentage - like Heucherella ‘Sweet Tea’ - your plants have superior heat and humidity tolerance.
5. Lily of the Valley (Convallaria majalis)
Lily of the valley is a woodland flowering plant , known for its pure white, bell-shaped pendant flowers and unforgettable perfume. It is often used as a shade-loving ground cover since it has a dense root system that will eventually crowd out weeds and create a lush carpet of green.
These plants do not do well in hot, dry areas. Harsh sun and high heat dry out their shallow root systems and kill the plants.
Plant instead: Creeping Lilyturf (Liriope spicata)
For hotter, drier summers, replace lily of the valley with hardy, heat-tolerant ground cover creeping lilyturf. These plants create a dense mat with long, grass-like leaves and pale violet or off-white flowers on short rachis. It suppresses weeds like lilies of the valley but survives intense heat waves while staying green.
6. Cosmos (Cosmos bipinnatus)
Cosmos are native to Mexico, which means that they generally like warm weather and direct sun. This extremely popular showy annual can grow to 2-4 feet (1m) tall on erect stems, carrying saucer-shaped, daisy-like flowers with red, pink or white petals and yellow centers. They bloom constantly from early summer to frost.
However, cosmos plants suffer in hot and humid summer climates. The flowers simply stop opening and the lovely colors fade. As temperatures climb, the plants can even wilt.
Plant instead: Purple Coneflower (Echinacea purpurea)
Looking for a flower that will thrive in soaring temperatures and dry soil? Look at the purple coneflowers. These North American natives also grow large, daisy-like petals with prominent, spiky center cones. But they are hardy perennials that have evolved to grow in extreme temperatures and lean, dry soil.
