5 signs your plants are suffering from heat stress – and expert tips to help revive them again

Summer is well and truly here as the temperatures continue to soar across the US. While we usually welcome plenty of sunlight and warmth for our plants, experts warn that too much heat can cause stress for plants and have a negative impact on their growth and appearance.

That's why it's important to protect plants in a heatwave - both for garden plants and even indoor plants that like direct sun. Too much exposure to high temperatures can set your plants off track, as they're not climatized to these growing conditions. This is especially true if you have a collection of plants that aren't native to hotter climates.

If your plants are looking a little droopier, aren't growing much or are simply reacting to the warmer temperatures in a negative way, they might be suffering from heat stress. Here are five common signs of plant heat stress and what experts advise to do if your plants are suffering this summer.

5 signs your plants are suffering from heat stress

Heat stress refers to when a plant is exposed to extreme high temperatures and their ability to grow happily is depleted, often harming their appearance. But your plant will start to tell you that it's suffering from heat stress long before it's too late to save it. Discover five common signs of heat stress below.

1. Wilted flowers

Just as we become thirsty in hotter temperatures, plants can also become dehydrated in extreme heat. For flowering shrubs and plants, and even the best indoor flowering plants, this can lead to witling blooms.

'Wilting happens when moisture levels in the plant are low,' says Thom Rutter, former professional gardener and content editor at Homes & Gardens. 'In extreme heat, moisture is drying up and evaporating more quickly so the plant isn't able to absorb sufficient water levels to support flowers,' he adds.

Typically, flowering plants that are otherwise healthy will bounce back as temperatures drop again. However, wilting is a sign that your plant is struggling in the heat and it may be time to water you plant.

So, if you find your hydrangeas are wilting or other blooms are wilting in the the summer sun, it can be wise to keep topping up their water levels. Just take care not to overwater outdoor plants. Try using this moisture meter from Amazon to help monitor and identify when your soil is too dry.

Thom Rutter

Thom is a Content Editor within the Gardens Team at Homes and Gardens. He has been working as a gardener and garden writer for several years. Whilst completing his Horticultural Traineeship at the Garden Museum, London, he was able to gain experience at many of the UK's world-famous gardens, including Sissinghurst, Lowther Castle, and Iford Manor. Following this, he worked for two private estates in Tuscany, Italy.

2. Yellow foliage

Whether you're caring for indoor plants or outdoor plants, all are at risk of yellowing foliage from heat stress. Similar to wilting, discolored foliage is another sign of a lack of moisture.

'When plants don't receive enough moisture, they are unable to pull water up through the roots to support healthy growth of foliage,' says Thom.

Plants need plenty of nutrients to grow well, which is why good soil health is vital. Watering helps to draw up nutrients from the soil to feed the plant and keep its foliage looking luscious. As heat dries plants out more quickly, roots aren't able to pull up water and provide those essential nutrients - making watering plants in a heatwave correctly a key part of summer care.

You might also find it helpful to use this soil test kit from Amazon to see which nutrients are present in your soil and if a deficiency is also causing discoloring foliage.

3. Scorched leaves

Alongside intense temperatures, too much exposure to the sun can cause foliage to become scorched and burned. While this is less likely to happen to indoor plants protected by windows, it can affect both houseplants and garden plants.

'Scorched leaves have crispy edges (kind of like overcooked pizza) and in severe cases, entire leaves can turn brown and die,' says Donna Letier, plant expert and CEO of Gardenuity.

Not only will plants suffering heat stress become scorched by overexposure to sunlight, but watering plants in hot weather incorrectly can also lead to leaf scorch. It's best to avoid getting foliage wet under extreme heat to prevent damage to leaves.

You may also find that some leaves are scarred by extreme heat and sun exposure. 'Sunburn on leaves will appear as white spots on leaves that are exposed to extended intense sunlight,' Donna adds.

Donna Letier

Donna Letier is the CEO and co-founder of Gardenuity, a company merging gardening with the wellness sector through personalized container gardens and gardening experiences.

4. Fruit and blossom drop

If you have a kitchen garden filled with beautiful fruit trees that offer a dazzling display of blossom in spring, you may find that heat stress causes both fruit and blossom drop. This is when plants drop their flowers and fruit before it is time to do so.

'Fruiting plants will have premature drop where flowers and new fruits may drop early as the plant prioritizes survival of reproduction,' notes Donna.

When plants are under stress from heat, energy and available water sources will be used to keep the plant alive rather than produce an abundant display of flowers and fruit. As a result, blooms and crops aren't being supported and will drop early.

This is also true if you are growing food in a greenhouse, so it's best to keep your greenhouse ventilated in summer to keep temperatures down and increase chances of a successful harvest. Using this fan from Walmart can help with ventilation.

5. No new growth

With all the stress of high temperatures and affected foliage, it's no surprise that heat stress can prevent plants growing well. If your plants have stopped growing right during their active growth season in summer, it's an indication that they aren't dealing with the hot weather very well.

'Heat stress puts plants into survival mode, so they won't direct any resources to new growth,' says Drew Swainston, former professional gardener and gardens content editor at Homes & Gardens. 'It's likely that you'll observe a lack of new shoots and leaves from plants under stress of extreme heat where they otherwise would at this time of year,' he adds.

This can also occur from other summer gardening mistakes, like over-fertilizing plants during their active growth season and causing root burn.

Drew Swainston

Drew qualified as a journalist and wrote for many websites and publications, before studying for a horticulture qualification. He worked as a professional gardener for several years, specializing in kitchen gardening. He's now bringing his expertise and passion to Homes & Gardens as a member of our team. 

How to revive plants from heat damage

Just because your plants are showing one or all signs of heat stress doesn't mean it's time to give up on them. Experts say there are a few things you can do to get them in fit shape again and protect them from further heat damage.

'To help your plant recover from heat stress you should first move them to a shaded area, if possible,' says Donna. It can be a good idea to move container garden plants suffering from extreme heat to somewhere with more garden shade, and you can even help protect plants in a more permanent position by using something like this patio umbrella from Amazon to cast shade over them.

'You should also water your plants deeply and thoroughly to ensure the roots receive adequate hydration, and trim off scorched or dead leaves and stems to reduce the plants' stress and encourage new growth,' Donna adds.

By taking away damaged plant matter, you allow the plant to direct more energy to new growth. Use essential gardening tools to do this successfully, like these Fiskars bypass pruners from Amazon.

FAQs

What temperature is too hot for plants?

The highest temperature plants can withstand will depend on their individual needs. For example, Mediterranean plants thrive in much higher temperatures than those native to the UK. That's why it's important to take some time to understand the US hardiness zone you live in and what plants grow best there during the highest temperatures of summer. If you are experiencing unprecedented high temperatures for your area, it's wise to put some precautions in place to protect your plants from heat stress and provide extra support until temperatures start to drop again.

It pays to take some extra care with plants during high summer heat because failing to do so could cause them to suffer from heat stress. If you notice some of these signs, it might mean your plant is in need of some help to get through the hot summer months.

Make sure to also keep on top of other essential care tasks and tick off everything on your summer gardening checklist.