How to treat sun scorched plants?

How to Revive Flowers Scorched by the Summer Sun

A common problem with both indoor and outdoor plants is that they can suffer from too much sun. The sun’s rays can stress a plant’s leaves to the point of dehydration, causing the plant to lose much of its green vigor. A sign that your plant has been overexposed to the sun is a collection of dark or bleached spots on the leaves. Often times, the soil beneath the plant will have little or no moisture, causing it to harden. If this happens to be the case with your plants, follow the instructions below for a quick fix. But remember, not all plants are easily revived, so have patience, and keep a good watch over your greenery.

Immediate Help
If your plant is indoors, remove it from direct sunlight and place it in a shadier spot. Changing a plant’s sun exposure can give it needed rest, but you must keep a close eye on its progress to be sure you have not placed it in too much shade. Shade, much like overexposure to sunlight, can easily disintegrate a plant’s health as overexposure to sunlight.

Next, for both indoor and outdoor greenery, you will want to water your plant, thoroughly. For outdoor fauna, this means soaking the ground at the plant’s base multiple times in a day. The soil has been hardened, and will take a few good soaks until it has been properly hydrated. For your potted greenery, or indoor flora, you will want to do the same. Let the soil have a full soak, and if possible, get the entire plant wet in the process, in order to cool it off. To keep your indoor plant’s moisture levels high, place the pot in a tray of water.

You will want to trim the dead or scorched foliage after properly watering. Your plant is expending energy on attempting to keep the burnt parts alive. Clip these areas off so that the energy it produces will go to the areas of the plant that are still healthy.

After you have completed this process, mulch underneath your outdoor plants. The mulch is necessary to keep the roots and soil both hydrated and protected from the sun’s rays. This is a good idea for any plants that seem to dry out in your yard.

Lastly, if you are worried you have a shady house plant in the sun, check the following list. Some plants that you should move away from the window include – moth orchids, flame violets, peace lily, thanksgiving cactus, most palms, coleus, snake plant, zebra plant, philodendron and ferns.

Sunburn in the garden is such a pain. I avoid it with a straw hat so wide of brim it could double as an umbrella, but my plants have no such defences. When the mercury hits 35, something fries. What suffers depends on the calendar. You’ll remember that we had our first 35-plus day in the first week of September. In my garden, the sun snuck through a still-bald frangipani to burn some ferns. Worse, the rays lasered the new foliage on the hibiscus. New leaf buds had just emerged when we endured our next scorcher. The plant is so knocked around it hasn’t produced a single flower so far this summer. (I’ve made a note to prune much earlier this winter so the new growth has a chance to harden off before the heat arrives.)

Now, at summer’s peak, even plants that like to grow in full sun are suffering sunburn. Anita Rayner, who heads the horticulture team responsible for Elizabeth Farm, Rouse Hill Farm, Vaucluse House and the other Sydney Living Museum properties, agrees it’s been a sunburnt summer. “You know it’s bad when the agapanthus burns,” she says. Wedding parties at Vaucluse House have been disappointed to find the lawn sepia rather than green and the top of the plumbago hedge at Rouse Hill has scorched. So what’s the plan? “My advice is to do nothing,” Rayner says. “The lawn will come back when it rains again, the plumbago will grow on.”

Burned leaves offer protection for the unburned leaves beneath themCredit:Simon Letch

Do nothing is good advice. The burned leaves offer protection for the unburned leaves beneath them, and cutting off dead foliage only encourages new growth, which is vulnerable to even more intense damage. Prevention tactics also help. Leave the lawn at least five centimetres long and don’t fertilise lawn or plants through summer to avoid creating soft new growth. Some gardeners also swear by Yates Droughtshield, which is a biodegradable polymer sprayed on leaves to reduce transpiration. It’s especially useful for leaves that wilt easily, like hydrangea. Delicate little treasures can be protected by creating temporary shelter, either with shade cloth or moveable bamboo screens. Patience is a longer-term strategy. Once the weather cools, plants that are too exposed can be moved, and more shelter, in the form of trees, can be planted.

In the short term, Rayner admits there are times when the recommendation to ignore the burn just can’t be followed. “It depends how unsightly it is,” she says. Exactly, which is why I was out this morning trimming burned stuff from my heliconia clump. It is just starting to produce flowers that, once they are fully open, look like hot-pink canoes being paddled by people dressed in yellow. It’s impossible to enjoy the show when the flowers are curtained by crispy brown rags, so I got to work with the secateurs. Now I have my fingers crossed for no more scorchers.

Crop plants soaking up sunlight. Image credit: kuhnmi via Flickr.

If you’ve ever experienced a painful sunburn, you know that ultraviolet light from the sun can be very damaging. So how do plants that bask in sunlight all day long avoid getting sunburn?

It turns out that plants can make their own sunscreen! These chemical sunscreens protect plants from harmful solar radiation while still allowing them to carry out photosynthesis, which is driven by sunlight. The natural sunscreens protect the plants much in the same way that sunscreens from the drugstore protect our skin from the dangerous effects of ultraviolet light exposures.

Back in 2011, a team of scientists reported in the journal Science that they had discovered a photoreceptor in plants that responds to ultraviolet (UV) light. Specifically, following exposure to UV-B light, which is the most harmful of the two forms of UV light (UV-A and UV-B) that reach Earth’s surface, plants start to modify the photoreceptor protein, named UVR8, inside their cells. This then triggers a variety of cellular responses such as the production of chemical sunscreens that absorb harmful UV-B radiation.

Diagram of different types of ultraviolet radiation from the sun. Image via Quora.

Professor Gareth Jenkins of the University of Glasgow, who was a co-author of the above study, commented on their findings. He said:

When a plant detects UV-B light this light stimulates the synthesis of sunscreen compounds that are deposited in the outer tissues and absorb UV-B, minimizing any harmful transmittance to cells below. This is exactly what our sun creams do. In addition, exposure to UV-B stimulates the production of enzymes that repair any damage to DNA. And lastly, genes are switched on that prevent oxidative damage to cells and help to maintain the photosynthetic machinery in the leaves.

Of course, plants can be damaged by the sun if their defenses are overwhelmed, but all in all, they excel at protecting themselves from UV light.

An explosion of research on plant sunscreens followed that initial discovery. For example, we now know that likely all plants, including single-celled green algae, produce these sunscreens. In fact, such sunscreens may have played an important evolutionary role in helping plants make the transition from the sea to land about 700 million years ago, as UV exposures are much more intense on the land than in the sea. Scientists have also shown that while some tropical species of higher plants produce high levels of sunscreens continuously, other plants can increase their production over the course of the day in response to changes in UV light similar to the tanning process.

Presently, scientists have begun searching for plant-based sunscreens that could serve as active ingredients in products intended for human use. There are already a few such products on the market in Europe, including one that contains a UV-A protective agent from marine red algae. Any alternative to current sunscreens should undergo a rigorous review to ensure that it protects equally well against UV exposures. Additionally, new products need to be tested for safety and be cost-effective to extract from plants or manufacture through other means. Scientists are even thinking about adding plant-based sunscreens to conventional sunscreens such as mineral oxides to see if these new compounds can increase the effectiveness of current products. Who knows, within another decade we could be slathering these plant-based compounds on our skin before heading outdoors.

Bottom line: Plants make their own chemical sunscreens that protect them from the harmful effects of ultraviolet light.

Deanna Conners is an Environmental Scientist who holds a Ph.D. in Toxicology and an M.S. in Environmental Studies. Her interest in toxicology stems from having grown up near the Love Canal Superfund Site in New York. Her current work is to provide high-quality scientific information to the public and decision-makers and to help build cross-disciplinary partnerships that help solve environmental problems. She writes about Earth science and nature conservation for EarthSky.

The one fact about plants that most people probably remember from school is that they use sunlight to make their own food. That process, photosynthesis, means that plants are dependent on sunlight. But as anyone who’s forgotten to put suncream on during their day at the beach knows, the sun can also be damaging. So how do plants absorb the light they need while avoiding damage from the sun’s ultraviolet (UV) rays? The short answer is by making their own sunscreen. And new research is helping us to understand exactly how that process works.

We know too much UV can be damaging to human health. In the short-term, excess UV – especially the shortest wavelengths in sunlight, known as UVB – causes sunburn. Repeated skin damage due to UVB exposure over decades can lead to an increased risk of skin cancers. Of course, different people can tolerate different amounts of UV. People with deeply pigmented (darker) skin are well protected all the time, whether they are out in the sun or not. Others need some exposure to sun to induce protective skin pigments by developing a sun tan. And some people barely tan at all, leaving them highly vulnerable to sunburn and other UV damage.

Of course we can all also choose to avoid the sun, wear a hat or use suncream. But what about plants? They have to stay in the sun. Is there a plant equivalent to sunburn or to the protective pigments we have in our skin?

Plant scientists really began to think about those questions when depletion of stratospheric ozone – the hole in the ozone layer – threatened to allow much more UVB to reach the Earth’s surface. Research back in the 1980s and 1990s showed that the high levels of UVB that would result from ozone depletion could directly damage photosynthesis. Other effects of high UV can also reduce growth and crop yields.

But the same body of research showed that plants are well-protected from the worse effects of the UVB levels we experience now. This protection comes from a suite of natural plant chemicals, mostly phenolics. These phenolic compounds act as natural sunscreens, strongly absorbing UV but not the wavelengths needed for photosynthesis.

Danger levels.

Just as with human skin pigments, the amount of these natural sunscreens varies between plants. Some plants, typically those that come from the tropics or from high-altitude mountains, have high levels of protection all the time. Others only produce sunscreens when exposed to higher levels of UVB, equivalent to tanning in humans.

That leads to another question. If plants produce their sunscreens based on their exposure to UV, how do they detect that exposure? And how do plants detect UVB?

UVR8 was first detected in Arabidopsis thaliana Wikimedia Commons, CC BY-SA

It has only been in the last decade or so that plant scientists have shown that plants detect UVB very specifically using a protein known as UVR8 (short for UV resistance locus 8). Plants that lack UVR8 cannot induce protective sunscreens and are severely damaged by the UV present in summer sunlight.

Researchers are still actively investigating the fundamental mechanisms by which UVR8 controls plant response to UVB. We’ve known for some time that UVR8 absorbs UVB, causing changes that ultimately allow the UVR8 protein to accumulate in the nuclei of the plant’s cells. This is a necessary step in the chain of responses that allow plants to protect themselves against UVB damage.

New research from the University of Geneva showed that UVB responses depend on interactions between UVR8 and another protein called COP1 (constitutively photomorphogenic 1). This protein interacts with other various molecules (HY5, SPA and RUP) in a plant’s cells to send a signal controlling the build up of sunscreen phenolics in response to UVB.

More sustainable crops

This might seem like an alphabet soup of abbreviations but the signalling system it represents affects us all through its role in the plants produced by farms as crops. We now know that plants use UVB as a signal to change their chemistry in ways that affects much more than just their UV protection.

UV exposure produces biochemical changes that can increase resistance to pest and disease attack. The UVB in sunlight improves the colour, taste and scent of fruits, vegetables and flowers. UVB exposure also increases levels of plant chemicals that are thought to be valuable in the human diet.

The new research adds to our increasing understanding that the UVB in sunlight shouldn’t be seen just in terms of damage. So long as we keep protecting the ozone layer, the effects of UVB will be just one part of plants’ normal responses to their environment. And the more we understand these responses, the more we can use that knowledge to produce more sustainable crops, improving their quality and reducing the use of pesticides.

Excess Light – Sunburn

Excess Sunlight

  • Some plants grow best in partial sun or shade. When shade-loving plants are exposed to full sun, leaf scorch or sunburn can occur.
  • Strong sun and heat cause the breakdown of chlorophyll in the leaf. Damage appears as pale, bleached or faded areas. These areas eventually become brown and brittle.
  • Symptoms are more severe when strong sun is combined with dry soil conditions.
  • Houseplants can be classified according to their light requirements: low, medium, or high.
  • Important aspects of indoor light are intensity, duration, and quality. Light intensity depends on the distance of the light source from the plant.
  • The brightest light is found in a south facing window, bay window or sun room. The duration is the length of time the plant receives light.
  • Most flowering houseplants are indifferent to duration. However, some houseplants such as Poinsettia, Kalanchoe and Christmas cactus only flower when day length is short, 11 hours or less. Plants need some period of darkness to develop properly; so do not expose them to more than 16 hours of light.
  • Artificial lighting can improve the quality of light the plant receives. Red, far-red and blue wavelengths are most important for plant development. Incandescent plus fluorescent light sources or horticultural grow lights best mimic natural sunlight.

Moving Houseplants Outdoors

  • Sunburn may also occur on houseplants that are adapted to low light conditions and moved directly outdoors without a “hardening off” period. To avoid sun scorch on houseplants, place plants in full sun for 2 hours per day initially and gradually increase the length of sun exposure.

Plants get sunburned, too, so plan to shade some edibles from the sun. From seeds that refuse to germinate in soil temperatures above 85 degrees, to lettuces and greens that bolt and beans that wither, heat can destroy crops, stop fruit production and invite disease.

When nighttime temperatures remain above 75 degrees, tomato blossoms don’t pollinate and drop off plants. As temperatures rise, tomatoes and other vegetables can develop sun scald, a gray scab on skins. And, tomato skins may split.

Some do like it hot. Melons, peppers and corn thrive in the heat, which makes them grow faster and bigger.

Steps You Can Take to Keep Plants Cool:

  • Mulch well. A 2-4” layer of mulch keeps plant roots cool and retains water. Be sure to use a light, natural-colored mulch instead of dark or dyed mulch.
  • Water early or late. Watering in the early morning, before the heat of the day, is best and prevents heat scald on your plants and rapid evaporation. A second watering may be needed in the early evening if heat is extreme.

Sun Protection:

  • Locate new transplants and seedlings in the shadow of taller plants. Look for opportunities to place smaller plants beside taller plants that provide partial shade.
  • Train tomatoes to a cage. Simply growing upright in the cage allows leaves to provide shade for the tomatoes. If sun and heat are extreme, draping a layer of cheesecloth over the cages adds some protection.
  • Protect large beds with hoops covered with shade cloth at least 12” above plants to lower air temperatures up to 15 degrees. For small areas, stretch shade cloth over tall stakes. Repurpose old window screens by staking them 12” above plants.
  • Plant greens, lettuces, bush beans and broccoli in spots where they get only morning sun and afternoon shade to keep them from bolting, or going to seed, so you can harvest longer into the season.


Heat makes lettuce bitter. If this happens, pick and rinse leaves with cool water, wrap in a paper towel and refrigerate overnight; the bitterness will disappear.


  • Cheesecloth
  • Tomato cages
  • Wood stakes
  • Shade cloth
  • Wire for making hoops

Scientists Discover How Plant Sunscreen Works

Plants are sun worshippers; they bask in it all day long, soaking up its rays so that they can generate energy from the process of photosynthesis. But they’re not immune to the damage that UV radiation can cause, and just like humans they need protection from it. Obviously, plants can’t slather themselves in sunscreen like we do, so how do they do it? According to new research, published in the Journal of the American Chemical Society, plants synthesize their own highly efficient biological “sunscreen.”

This sunscreen comes in the form of a group of molecules called sinapate esters which are found near the leaf surface. These chemicals have a dual role: they absorb photons of light for photosynthesis while also protecting against the damaging effects of UV. The most important of these compounds is sinapoyl malate, which provides the majority of the sun shield.

While researchers were aware of sinapoyl malate in plants, they didn’t know how it carried out its UV filtering role. To find out more, a team of scientists led by Purdue University’s Timothy Zwier began intensely probing the compound in the lab

In order to record the spectrum of UV light absorbed by sinapoyl malate, they began by using a laser to transition the molecule from a solid into a gas. Next, they brought the substance to close to absolute zero (-273.15oC or -459.67oF), which makes the spectrum easier to interpret. Absolute zero, or zero Kelvin, is the point where no more energy can be removed to a system. Finally, they used three different lasers to analyze the shapes the molecule adopted as it absorbed different wavelengths of UV-B light, which is known to damage both plant and human DNA.

They found that sinapoyl malate was remarkably efficient at absorbing UV light. In fact, its efficiency was one of the highest that can be achieved, absorbing all wavelengths of UV-B radiation with “no gaps in coverage,” according to Zwier. This broad spectrum, he says, is key to a good sunscreen, because it blocks all the harmful radiation.

“This is about the biggest absorption efficiency you can find in a molecule,” added Zwier. “So it does an excellent job capturing the UV-B light while letting other wavelengths of light necessary to plant life slip right through.”

While this molecule may be incredibly efficient at blocking harmful UV wavelengths, the researchers have no intentions to use it to develop human sunscreens. That’s because other natural substances, called cinnamates, that are already used in sun lotions are just as good. However, they could use this information to produce plants that are even more resistant to UV radiation.

Sunscreen for fruits, veggies? Farmers try it

FRESNO, Calif. — Sunscreen for fruits and vegetables is being tested in Australia and Chile, and now California farmers are checking it out courtesy of a local vendor.

Just like people damage their skin in the sun, produce can also get nasty burns. That’s why farmers are increasingly applying sunscreen to their crops to prevent skin blistering, heat stress and blemishes.

Sunspots on a Granny Smith apple can mean the difference between the lowest price for juice or the more lucrative fresh fruit market. As for nuts, last year buyers paid on average 3-cents a 1 pound more for sunscreen-protected nuts than untreated ones, said grower Ed Lagrutta as stood in the bed of his Chevy Silverado inspecting a San Joaquin Valley walnut grove in its second year of sunscreen tests. With yields topping 2,000 pounds an acre, it adds up, he said.

“With the costs of production going up, growers are looking to increase their margins wherever they can,” said Lagrutta, an adviser for Western Farm Services who farms 20 acres and runs tests on hundreds more.

Climate change and drought in Australia and California’s Central Valley have meant challenging growing conditions for farmers that are affecting the quality, yields and price of produce. Sunscreens alleviate at least one worry for farmers, who lose money with each fruit or vegetable that develops sun damage.

“I spend a lot of time studying drought,” said Eric Wood, Ph.D., a professor of civil and environmental engineering at Princeton University and an expert on hydrology and climate change. “Under climate change, heat stress will become a bigger issue for plants, especially when it creates new heat-released disease. Corn under stress is reflected in smaller ears and lower yields.”

Plants react to sun stress like humans. They perspire — a process called transpiration — which means the more temperatures rise, the more water they need. As drought grips several of the world’s key growing regions, scientists are looking at ways to conserve by helping plants use less.

SPF 45
Liquefied clay has been used for years, but now a California company is finding positive results with an SPF 45 product made of multicrystaline calcium carbonate crystals that are engineered to specifically deflect ultraviolet and infrared light from the plants and trees on which it is sprayed. The product keeps out the bad light, but lets in the good photosynthesis rays that aid ripening.

The sunscreen has been tested in Australia and Chile, where UV rays affect production, and is in the second year of field tests in California.

Tests show its immediate impact is increasing yields by diminishing stress and heat-related defects, but officials at Purfresh in Fremont hope the product also can play a role in water and energy conservation by increasing a plant’s water efficiency.

“We are where Silicon Valley meets the Central Valley,” said Purfresh chief executive David Cope, who left information technology after 25 years for what he describes as “clean technology.”

“We’re using technology to address food and water availability, which affects consumer prices,” he said.

Gary Kazanjian / AP These walnuts seen last Wednesday in Exeter, Calif., were not protected from the sun. The company has gained attention for its ozone sanitation system for water, produce packing and cold storage stabilization.

But it was its new sunscreen Purshade that lured 20 U.S. and international farm product researchers and advisers to a walnut grove near Visalia, Calif., last week.

The product also is being tested on tomatoes, grapes, kiwis and lychees in Australia, said Kerrie Mackay, who works for a company that sells crop protection products in Queensland, which she says is in 140-year drought.

“Sunburning is a big problem for us,” she said watching Lagrutta compare the telltale yellowing on one block of walnuts with a uniformly green plot sprayed with Purfresh. “We have some of the highest UV intensity in the world. With drought and climate change, finding ways to use water more efficiently is always important to us.”

Winery’s been using, too
Amador County’s Shenandoah Valley in the arid Sierra Nevada foothills is far from the temperate Napa Valley, but Dick Cooper of Cooper Vineyards has been growing 100 acres of premium wine grapes since the 1980s by using vine canopies to shade bunches. When vines transpire, they don’t use the water to produce stems, leaves and fruit. In dry years like this one vine vigor is slow and exposed bunches of his pinot grigio shrivel into something resembling an olive pit, he said.

For the second year, he sprayed Purshade sunscreen on several of his blocks of white grape varietals to help protect them. He says that during the crush the calcium carbonate crystals drop to the bottom of the fermentation tanks with the rest of the sediment that comes in on grapes, so taste isn’t affected.

“I’m not an expert on anything, but I’m always interested in trying anything,” he said. “When my vines don’t put up enough canopy, I like to give them a little help.”

Plant Leaves Turning White Or Pale: Learn About Plant Sunburn Damage

Bringing home new plants from the nursery is one of life’s greatest joys for gardeners the world over, but when you’ve only just started in the garden, there are a lot of things that other gardeners assume you already know. They figure you know how to properly water, fertilize and care for your plants and neglect to point out these things that they find obvious – another often overlooked, yet valuable, bit of information can prevent your plants from turning white when the heat of the summer is bearing down.

What Does Plant Sunburn Look Like?

Plant leaves turning white is often the first, and sometimes the only sign of leaf sunscald in plants. You can think of this problem as plant sunburn damage and you won’t be far off from the truth. In a greenhouse, plants are exposed to high levels of filtered or artificial light, so they grow leaves that are good at soaking up those wavelengths. The problem with taking a plant straight from the greenhouse to your full sun garden is that they aren’t prepared for the extra UV rays they’re getting outside.

Just like you turn beet red if you forget the sunscreen on your first long day outside in spring, your plants can experience sun damage to what is essentially their skin. The outer layers of leaf tissue burn up with so much light exposure, causing light tan to white discoloration on the leaves and stems of tender plants. In some instances, established plantings can suffer from this as well, especially during an unexpected and extended heat wave (meaning more intense sunlight and UV rays). Vegetables and fruits can also suffer the same kind of sun damage if something causes your plants to suddenly defoliate, exposing fruits to excessive light.

How to Protect Plants from Sunburn

Sunscald injury of plants is easy to prevent, though there is no cure. Once leaves are damaged, all you can do is support the plant until it manages to grow new, stronger leaves. Slower acclimation to bright sun, known as hardening off, is vital to promoting sun resistant leaf development and preventing plant sunburn damage.

For plants already suffering, use a sunshade to restrict their exposure to UV light. Slowly give them more time each day with the sunshade removed until they are toughened up. This process can take about two weeks, at which time your plant should be ready for the sun. Make sure you properly water and feed plants with sunscald while they’re trying to recover — they’ll need all the support they can get.

This is Part Four of a seven part series on some quirks that can be found with tomatoes. If you are interested in the other Tomato Quirks articles, here are the links:

Tomato Quirks Part 1 – Catfacing

Tomato Quirks Part 2 – Bumpy Stems

Tomato Quirks Part 3 – Green Shoulders

Tomato Quirks Part 5 – Splits & Holes

Tomato Quirks Part 6 – Spotted Tomatoes

Tomato Quirks Part 7 – Leaf Roll

What Is Sunscald?

Sunscald occurs when the green or ripening tomatoes are exposed to direct sunlight for extended periods during very hot weather. This exposure to direct sunlight can cause hard and discolored patches on the ripening tomatoes. These patches will then blister over time and eventually become sunken. Once the area has begun to sink on the tomato, it will grow a paper-like, thin, grayish-white substance. The sunscalded area may also begin growing black mold which will rot the tomato, and render it inedible.

How Can I Prevent Sunscald?

Sunscald can be prevented and controlled in many ways. Try not to remove too much foliage from the tomato plant when pruning. The extra foliage can help shade the fruit during extremely hot weather, and block the direct rays from the sun.

You can also use a shade cloth to shade the plants during the hottest part of the day. Use the shade cloth to build a tent over your tomato plants.

Growing the tomato plants upside down can also help to prevent sunscald. The leaves of the plant, and the container that houses the plant, will shade the fruit much better.

If you feel that sunscald might be an issue, or is an issue with your tomatoes, you can pick the fruit when it is still green, and allow them to fully ripen indoors. Place the tomatoes in a window sill, or under a skylight if possible. Just as long as the tomato receives some indirect light, it should ripen just fine.

When sunscald is in the early stages of development, it is best to pick the tomato and let it finish ripening indoors. The tomato is still probably edible – just cut away the affected areas. If the tomato shows any signs of black mold or rot discard it immediately, or add to a compost pile.

Part Five of Tomato Quirks will be on tomato splits and holes. Be sure you don’t miss it by subscribing to our RSS feed, or by bookmarking us.

Grow Fantastic Tomatoes

Leave a Reply

Your email address will not be published. Required fields are marked *