David Kuchta, Ph.D. has 10 years of experience in gardening and extensive reading of environmental history and energy transition. Since the 1970s, he has been an environmental activist, as well as a historian, writer, gardener, and educator.
In a world of increasing heat, drought and heat waves, sunburn is becoming an increasing threat to plant health. Whether indoors or outdoors, sunburn is fatal to plants, and it is easy to mistake it for something else.
But correctly identified and handled, your plants can survive. An ounce of prevention is better than a pound of treatment: first, there are some ways to prevent plants from sunburning.
Sunburn and sunburn are two different ways that excessive exposure to the sun can harm plants. When the leaves begin to lose their color, sunburn will appear, turning pale green or even white in some cases, or yellow and brown in other cases. Withering first appeared in the leaf veins, and then gradually spread to the tip of the leaf.
It is often mistaken for sunburn, which affects the bark and fruit. Like dehydrated skin, the bark and fruit will crack, which can cause insects and diseases. The bark may develop ulcers and destroy the cambium directly below the bark, where water and nutrients flow through the tree. Without this flow, the leaves above the damaged area would die, exposing more trees to the sun.
Among commercial fruit growers, sunburn is considered to be one of the more important physiological stresses on plants because it can cause crop damage and consumer rejection of the fruit.
As we all know, in humans, prolonged exposure to ultraviolet (UV) light is the cause of sunburn. However, in plants, excessive sun exposure may be the direct cause, but for indoor and outdoor plants, insufficient soil moisture is the ultimate cause of sunburn. This is why ordinary sunlight and ultraviolet rays can cause sunburn on plants. Dry plants cannot withstand the extra pressure of strong sunlight.
In response to the long-held belief that watering plants at noon will cause sunburn, researchers have proven that water falling on plants with smooth, hairless leaves (such as maples) will not damage the leaves, while watering at noon will cause sunburn. Damage to plants (trichomes) whose leaves contain plant hair, such as ferns. In general, trichomes can effectively absorb UV-B radiation and limit its damage, but the water suspended in the hair of plants can intensify sunlight and cause burns.
Other stress factors include low humidity, low night temperature and strong noon sun, as well as various gardening practices, such as the way of pruning or shaping trees or shrubs. For example, excessive pruning exposes lower branches and bark to excessive solar radiation, while heat and light radiated from walls (especially concrete or brightly colored surfaces) can cause plants that are not suitable for these areas to burn.
Proper care of plants can reduce the risk of sunburn. For indoor plants, be sure to read the label. Indoor plants are generally more suitable for weak sunlight than outdoor plants, and they are more prone to sunburn if placed in the wrong location. For example, the emerald plants on the windowsill are easily sunburned during the hottest part of the day. For jade and many other plants that like strong light but don't like direct light, a radiation screen on sunny days can block ultraviolet rays and reduce the risk of sunburn.
When moving indoor plants outside, place the plants in the greenhouse until they mature, because the greenhouse filters ultraviolet rays. If there is no greenhouse, gardeners will usually "harden" their plants by gradually introducing them into more direct sunlight. It is common practice to expose indoor plants outside for one hour a day for two weeks.
Unless the damage is extensive, plants can recover from sunburn. Just remove any damaged leaves, protect the plant with a shading cloth until you see new growth, and water heavily.
The risk of sunburn is just one of the many reasons for choosing native plants, especially those suitable for the USDA plant hardiness zone. Native plants have been adapted to your climate for thousands of years. In areas prone to periodic drought, consider dry farming. Desert-friendly trees and shrubs have thicker, waxier flesh and thinner leaves, thorns or needles, which can reduce water loss and provide a protective layer against strong sunlight.
If soil moisture is the ultimate cause of sunburn on plants, then the best advice to prevent sunburn is watering, watering, watering-and then using compost mulch to protect soil moisture. Keep the mulch away from the base of the plant to reduce the possibility of disease spreading to the dry, cracked bark.
In addition, make sure that nothing hinders root growth (and water absorption). The root growth on a tree or shrub is usually the same as the width of its canopy, so planting widely distributed trees or shrubs next to deep foundations means that plants can only extend their roots in three directions instead of four.
The link between sunburn and climate change is obvious. Rising temperatures, droughts and heat waves are the main sources of water stress that cause sunburns and sunburns. In cash crops, sunburn can cause millions of dollars in damages. Therefore, the main but indirect way to prevent plants from sunburn is to deal with climate change. This will require more than an ounce of prevention, but it will bring more than a pound of treatment.
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Munné-Bosch, S. and C. Vincent. "The physiological mechanism of fruit sunburn." Critical Review of Plant Science 38:2 (2019), 140–157. https://doi.org/10.1080/07352689.2019.1613320.
World Health Organization. Prevent exposure to ultraviolet radiation. Geneva: World Health Organization, 2001.
Severino, V. etc. "Climatic and physiological parameters related to the progress and prediction of apple sunburn in the neotropical climate." Advances in Horticultural Science 34:4 (2020), 431–440. DOI: 10.13128/ahsc9764; Makereza, Brian, etc. "Water stress can increase sunburn on'Cripps' pink' apples." Horticultural Science 48:4 (April 2013), 444-447. https://doi.org/10.21273/HORTSCI.48.4.444.
Ray, Ray. "Prevent sunburn." Nature Plant 3 (March 1, 2017), 17026. http://doi.org/bzj2.
Egri, Adamu and others. "The optical effect of water droplets on leaves under sunlight: conditions that may be sunburned." New Botanist 185:4 (March 2010), 979-987. https://doi-org.une.idm.oclc.org/10.1111/j.1469-8137.2009.03150.x.
Liakoura, V. etc. "The trichome density and its UV-B protection potential are affected by the shadow on the canopy and the position of the leaves." Environmental and Experimental Botany 38:3 (December 1997), 223-229. https://doi.org/10.1016/S0098-8472(97)00005-1.
Makereza, ibid. Quote; Xue Xiaomin et al. "The interaction between night temperature and sunlight intensity affects the anthocyanin biosynthesis and photooxidative sunburn of the'Fuji' apple." Frontiers in Plant Science (July 23, 2021). https://doi.org/10.3389/fpls.2021.694954.
Holstein, Christoph, etc. "The effect of low-haze diffuse glass on the production and light distribution characteristics of greenhouse tomatoes and sweet peppers." Plant 9 (2020), 806. doi:10.3390/plants9070806.
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