How Long Can Plants and Flowers Survive in a Hot Car?

By Richard Flowers, ACCNP, Green Thumb Nursery, Ventura

Most people know that leaving your child, other humans, or dogs in a hot car for any length of time can have catastrophic consequences. You should not forget your plants, either — they can suffer from sunburn and heat damage just as badly.

It’s a beautiful Saturday, the sun is shining, and the temperature is warm. You pop into your favorite Green Thumb Nursery, pick out the plants you adore, and can’t wait to get home. On the way, you run a few errands and go shopping. You arrive home a few hours later and, to your surprise, the plants you bought look horrible. What was once vibrant and healthy is now wilted, burned, and withered; the flowers have faded, leaves are dropping, and the foliage has necrotic (dead, brown) areas. You ask yourself: what happened?

How Hot Does a Parked Car Really Get?

Hotter, and faster, than almost anyone expects. According to the National Highway Traffic Safety Administration, the inside of a car heats up by nearly 20°F in just the first 10 minutes. The classic San Jose State University vehicle-heating study (Jan Null) found an average rise of about 19°F at 10 minutes, 29°F at 20 minutes, 34°F at 30 minutes, and 43°F at an hour — and the National Weather Service notes that cracking the windows barely slows it down, because sunlight heats the dashboard and seats to 180–200°F and they radiate heat into the trapped air.

Interior temperature rise based on the San Jose State University / Jan Null vehicle-heating data. On an 86°F day, a closed car reaches roughly 120°F within half an hour — which matches what I measured myself (below).

What Heat Does to Plants

Most plants are happiest between about 68°F and 86°F; above that, heat stress sets in, and the 120°F-plus of a closed car is far past what soft tissue can take. High heat pulls water out of flowers, leaves, and stems faster than the roots can replace it, which causes wilting and leaf scorch — the outer leaf margins dry and burn first, and in severe cases the cells die, leaving the brown necrotic patches you see on a cooked plant. The effect is worst on houseplants, cut flowers, and other soft-tissue, tropical material.

Heat is not the only problem. A closed car has low humidity and stagnant air, and that combination stresses plants further — many flowers need a certain humidity to stay fresh, and stagnant air around cut stems can encourage bacterial growth that shortens vase life.

My Firsthand Car-Temperature Test (March 2026)

I documented the effects of car heat on plant material myself during a strong March 2026 heat wave. The temperature outside was 86°F. The temperature inside the car, sitting in the sun with the windows up, was a whopping 120°F at 20% humidity. I moved the car into the shade and recorded it again a little while later: 106°F and 21% humidity — still far too hot for plants in an enclosed car. The glass acts like a magnifying glass, the car’s dark color absorbs heat, and the heat is trapped with nowhere to go. This microclimate really did a number on the tropical plants.

After that episode, I moved the plants into the shade, watered them thoroughly right away, and trimmed off the badly affected parts. Weeks later, in early May, the tropical houseplants still looked rough — the brown, scorched areas never turned green again — but a little new growth was emerging at the top, a sign of slow recovery. Heat waves are becoming more common and can hit any time of year, so any time in a hot car is too long for our plant friends.

What to Do If You Left a Plant in the Car

It happens. If you catch it in time, you can often save the plant:

• Get it into cool shade first — out of direct sun before you do anything else.
• Water deeply, but don’t drown it. Give the roots a thorough soak; heat-stressed plants should not be overwatered — keep the soil moist, not soggy, and skip fertilizer until it recovers.
• Trim the dead parts. Remove crispy, scorched leaves and stems so the plant can put its energy into new growth.
• Be patient. Keep it out of direct sun for a few days and give it time — many plants come back if the roots are healthy.
• For cut flowers, re-cut the stems at an angle and place them in cool water.

Better yet, prevent it: water plants before a hot trip, run the A/C for a few minutes before the plants go in, park in shade and use window sunshades, and keep travel time short — do your other errands first, then pick up your plants last.

Wait. Only time will tell whether a cooked plant will recover and push out new growth. Some plants regrow from their roots or stems and go into survival mode; others are less resilient, as every plant is different. From my own experience, most plants will come back — they just need some time, love, and care. Stop by your favorite Green Thumb Nursery and we’re happy to advise you.

Richard Flowers is an Advanced California Certified Nursery Professional (ACCNP) at Green Thumb Nursery in Ventura, California.

Plants and Flowers in a Hot Car: FAQs

Can flowers survive in a hot car?

For a short time, but not long. Cut flowers and potted plants are very sensitive to heat — a parked car can reach 120 to 140°F within an hour on a warm day, which wilts blooms and scorches leaves fast. Flowers often show damage within 20 to 30 minutes in a hot car, so keep the car cool, park in shade, and get them inside quickly.

How long can plants or flowers last in a hot car?

Not long on a hot day — usually under 30 minutes before heat stress begins and under an hour before serious damage. The hotter the day and the more direct sun on the car, the faster it happens. On a mild day parked in shade, an hour or two may be fine. Never leave a plant or flowers in a closed car overnight in warm weather.

Can you leave a plant in the car overnight?

Avoid it in both hot and cold weather. Overnight heat, or a cold snap, in a closed car can kill a plant through heat stress, dehydration, or frost. If you must transport a plant and cannot bring it inside, crack the windows, park in shade, and move it indoors as soon as possible.

Will plants die in a hot car?

They can. Extreme heat causes wilting, leaf scorch, and dehydration, and a few hours in a hot, sunny car can be fatal — especially for tender new growth, flowers, and tropical plants. Caught early, many plants recover (see above for what to do).

What should you do if your plant or flowers wilted in the car?

Move them into cool shade right away, give the roots a deep drink (soak a potted plant for about 30 minutes), mist the foliage, and remove any crispy or badly scorched leaves. Keep the plant out of direct sun for a few days while it recovers. For cut flowers, re-cut the stems at an angle and place them in cool water. Many plants bounce back within a week if the roots are still healthy.

Did a plant not survive the ride home? Green Thumb Nursery stocks healthy indoor plants and outdoor plants at our five Southern California garden centers — and our Certified Garden Experts can help you pick a replacement and get it home safely.

Sources

• Child Safety / Heatstroke, NHTSA
• Vehicle Heating Dynamics, Jan Null, San Jose State University
• Children, Pets and Vehicles, National Weather Service
• Heat Stress on Plants, University of Maryland Extension
• How to Recognize Plant Heat Stress, Utah State University Extension
• Don’t Overwater Heat-Stressed Plants, University of Missouri Extension

Sources:

• National Highway Traffic Safety Administration
• San Jose State University vehicle-heating study (Jan Null)
• the National Weather Service notes
• about 68°F and 86°F
• wilting and leaf scorch
• heat-stressed plants should not be overwatered