How Hot Is Too Hot For Plants

Perennial Garden in Summer Heat

Caring For Plants During A Heat Wave

Summer is here and once again it’s delivering a one-two punch of brutal heat waves. Temps are skyrocketing for long periods of time and we humans must remember to keep hydrated and find clever ways to cool down.

But what about our plants?

Plants can’t dive into a nice cool lake or drive over to the mall to enjoy the free AC. They’re stuck dealing with heat and blaring sunlight, like it or not. And while they have some temperature-regulating tools built into their biology, there’s only so much heat they can take.

So, how hot IS too hot for plants?

The general answer is around 90 degrees F, with some exceptions to the rule. This means that when temps rise above 90 and remain there for a lengthy spell:

  • Leaves wilt. Water evaporates into the atmosphere more quickly in high heat, draining a plant’s reserves. This is especially true in dry heat.
  •  
  • Flowers, especially young blossoms, drop. Some plants need to forfeit their reproductive goals in order to use their available energy to manage their own cooling systems. Heat waves can mean fewer flowers.
  •  
  • They stop breathing to prevent water loss. Harder to see, but some plants will close their leaf pores (stomata) to keep water from evaporating. This comes at a high price, as the pores must remain open to take up carbon dioxide, which is critical to photosynthesis. Plants with limited CO2 are slower to grow and may attract pests due to a weakened immune system.
Watering Perennials on a Hot Day

What can we gardeners do about it?

Plant the right kind of heat-loving plants for your environment, be it dry or humid. Tropical plants like hot, sticky weather while xeriscaping (drough-tolerant) plants thrive in high-temperature climates that see little rain fall. Both sets of plants are standout choices for enduring heat waves, as they're already adapted to those conditions.

Water and Mulch. Whenever it's over 90, be sure to give your plants plenty of water. This will prevent wilt and give them the freedom to manage their internal systems without worrying about losing too much moisture. By mulching your plants early on (and refreshing the mulch 1-2 times throughout the season) you'll help to keep the surrounding soil cool and limit water loss.

Build healthy soil. Good soils mean more water-holding capacity and less evaporation. Perennial plants are best-positioned to survive extreme temps when their roots run deep and wide and healthy soils make this type of self-care possible.

Plant Defensively. Create some shade, especially from afternoon sun. This may mean planting a large shrub, bush, or structure on the western side of your favorite perennials, or it may mean intentionally revamping a large area, making it a Shade Garden. With the ability to lower temps in your yard by fifteen degrees, you and your plants will appreciate a shady retreat.

  1. Hameln Fountain Grass, Pennisetum alopecuroides

    'Hameln' Fountain Grass is a smaller variety with three distinctive seasons of stunning displays in full sun or part shade gardens. First, fine-textured green grass blades up to 3 fe...

    Learn More
    Hameln Fountain Grass Hameln Dwarf Fountain Grass Pennisetum alopecuroides Hameln
    As low as $12.65 Sale $9.49
    Per Plant - 3.5" Pot
    'Hameln' Fountain Grass is a smaller variety with three distinctive seasons of stunning displays in full sun or part shade gardens. First, fine-textured green grass blades up to 3 feet tall are tipped with soft, wheat-shaped seed heads. Foliage turns rust gold in autumn, and finally, pale blonde in winter. 'Hameln' is a favorite for birds and resists hungry deer. A great match for late-season perennials and colorful shrubs in the mixed border, as well as cut or dried flower arrangements. (Pennisetum alopecuroides)
  2. Blue Spruce Sedum, Sedum reflexum Blue Spruce

    This Sedum gets its name from small, blue leaves that resemble the needles of a blue Spruce. Cheerful yellow flowers emerge in the early summer. (Sedum reflexum)...

    Learn More
    Blue Spruce Sedum Blue Spruce Stonecrop Sedum reflexum Blue Spruce
    As low as $9.32 Sale $6.99
    Per Plant - 3" Pot
    This Sedum gets its name from small, blue leaves that resemble the needles of a blue Spruce. Cheerful yellow flowers emerge in the early summer. (Sedum reflexum)
  3. Sensational!™ Lavender, Lavandula x intermedia Sensational!™ harvested in a baskest

    Sensational!™ Lavender is an improved, easy-to-grow variety that makes growing lavender accessible to more gardeners than ever! Silvery foliage is topped by large, dense purple flo...

    Learn More
    Sensational!™ Lavender Sensational!™ Lavender Lavandula x intermedia Sensational!™
    As low as $9.99 Sale $8.99
    Per Plant - 3" Pot
    Sensational!™ Lavender is an improved, easy-to-grow variety that makes growing lavender accessible to more gardeners than ever! Silvery foliage is topped by large, dense purple flower spikes. With a compact, dense habit and notable durability for sun, heat, and humidity, as well as cold tolerance, Sensational stands apart from many traditional Lavender varieties. A favorite of honeybees, these fragrant flowers will attract a wide range of pollinators. (Lavandula x intermedia)
  4. Mini Pollinator Pit Stop Plant Collection

    Give bees, butterflies, and hummingbirds what they need with our Mini Pollinator Pit Stop Plant Collection. Compact varieties of Butterfly Weed, Bee Balm, and Salvia are ideal for...

    Learn More
    Mini Pollinator Pit Stop Plant Collection Mini Pollinator Pit Stop Plant Collection
    $26.65 Sale $23.99
    Per Collection of 3
    Give bees, butterflies, and hummingbirds what they need with our Mini Pollinator Pit Stop Plant Collection. Compact varieties of Butterfly Weed, Bee Balm, and Salvia are ideal for small-space gardens and patio planters, supplying a consistent supply of nectar. A mix of popular, easy-to-grow perennials, these showy pollinator plants will delight with bright colors for years to come. Collection of 3 plants.

To learn more about the plants we sell and how to grow them in your garden beds and patio containers, sign up for our inspiring emails.

© 2021 AmericanMeadows.com All rights reserved