Every leaf on a tree or plant has a lifespan, even in evergreens. After which, you might notice tree leaves turning yellow (chlorosis) and fall onto the ground. In evergreen trees such as conifers, the average lifespan of leaves is three years. In contrast, deciduous trees drop their leaves in the fall and produce new buds each spring.
As these leaves mature, bring the dense and lustrous greenery on trees—one hallmark of summer. However, in less-than-perfect conditions, the leaves on trees and indoor plants turn yellow, weak, and translucent. This leaf yellowing is due to chlorosis—a condition associated with a lack of chlorophyll.
Besides chlorosis, several factors lead to tree leaves turning yellow, such as diseases, pest invasions, and the plant’s aging process. Continue reading to learn more about why tree leaves turn yellow and how to treat them.
10 Reasons Why Tree Leaves Turning Yellow
One of the leading causes of tree leaves turning yellow, particularly in summer, is a lack of chlorophyll ( also known as chlorosis). It involves leaf yellowing the entire surface while the veins remain green.
The reason for this chlorophyll lacking or washing is not pathogenic but the deficiency of iron and manganese in foliage. Such nutrient deficiency is prevalent in alkaline soils (having a pH value above 7.2), which makes these nutrients unavailable to plant roots.
Under severe nutrient unavailability, the foliage turns pale green and falls to the ground prematurely, thus leaving the tree bare before autumn. This condition is more common in grapevine, eastern pin oak, river birch, and red maple leaves.
Note: Chlorophyll is an essential molecule in leaves for photosynthesis and their green color.
Lack of Enough Light
Sunlight is critical in plants’ healthy growth and development because it ensures food production through photosynthesis. It also assists the plant in water and nutrient absorption, and when your plants are not receiving enough light (not planted in full sun locations), their foliage begins turning yellow.
Note: For potted plants, it is much easier to cure the yellowing leaves by positioning the planter in a sunnier location. In the case of inground plants, providing them with ideal sunlight locations becomes challenging. Therefore, it is best to choose a garden or landscape site where they receive perfect sunlight.
Too Much Sunlight
Too intense sunlight also causes chlorophyll breakdown, which leads to leaf yellowing. It also dries the soil through evapotranspiration by warming the surfaces, making it difficult for the plant root systems to absorb water properly.
For plants that do not need much sunlight for healthy growth, this intense sunlight can burn their full foliage and plants. So it is best to grow plants in sites that provide ideal sunlight locations. Such as tropical plants can take full sun for more than six hours per day compared to hostas.
Too much watering of potted plants and landscape trees turns their foliage yellow and brown. It is because excessive soil moisture blocks the oxygen supply to roots. This also negatively impacts nutrient and water absorption, leading to the complete yellowing of the aboveground plant parts.
Note: Poor drainage and overly wet soil promote root rot and the growth of soil-borne fungal pathogens. Such conditions also turn the tree leaves yellow.
Yellow leaves are also a sign of water scarcity of potted and garden plants. Because plants need water to carry out the food-making process correctly, and in underwatered soils, they cannot photosynthesize (sometimes, it gets worse when there is not enough light).
Improper nutrient supply in plants also leads to the yellowing of leaves. Nitrogen, iron, magnesium, and manganese are the main culprits the turning tree leaves yellow when not abundantly present in the soil. The only reliable way to treat these nutrient deficiencies is to perform a soil test and maintain optimum pH levels.
Yellow Leaves due to Pest Invasions
Insect pests such as spider mites, aphids, whiteflies, and mealybugs cause the yellowing of leaves. The damage to their feeding is more common in indoor houseplants and vegetables, leading to no flower production.
These bugs rarely kill the plant in vegetables but majorly reduce production due to severe foliage damage. They lead to premature foliage dropping and prevent leaf buds from opening. The only and best solution to avoid leaf yellowing is spotting pest infestation and employing proper management practices. Such as the use of neem oil and insecticidal soap spray.
Tree Leaves Turning Yellow due to Microbial Infections
Many microbial agents, such as fungi and bacteria, turn the tree leaves yellow and brown (necrotic lesions). The fungal infections start with yellow spots surrounded by dark brown rings or dead cells. It is caused by an early blight pathogen (Alternaria solani).
Another fungal pathogen that causes leaf yellowing is Fusarium wilt. In this disease, one side of the leaves turns yellow and curls downward. During severe disease infection combined with underwatering, plants dieback due to little to no photosynthesis and nutrient absorption.
Pesticide or Herbicide Injury
Pesticide or insecticide applications during warm, windy days injure the plants and their top leaves, thus leading to yellowing and premature drooping of leaves. Also, insecticide applications during drought and excessive flooding promote foliage burning and yellowing. With such damage, there is nothing to do with yellow and burned leaves except pruning them to boost the plant’s new leaf bud production.
High Soil pH
Chlorotic leaves indicate improper soil pH because highly acidic and alkaline soils impact nutrient availability. For example, alkaline soils influence the absorption of iron, zinc, and magnesium through roots. Similarly, boron and calcium-deficient soils turn the tree leaves yellow and cause deformities.
Sudden Temperature Change
High temperature causes heat stress and evapotranspiration, leading to the yellowing of trees. It leads to the dropping of leaves for extended exposure to temperatures above 95 degrees Fahrenheit.
Note: If a plant is exposed to sudden temperature changes (high and cold), its foliage turns yellow with brown tips, appearing similar to an underwatered plant.
The best and main way to treat tree leaves turning yellow is to provide them with ideal growing conditions. It includes no exposure to high and cold temperatures, optimum soil pH, and a wise watering schedule. The given below are the best management tips to prevent the tree leaves from yellowing;
- Always perform a soil test to determine its pH and nutrient levels. It will help the growers to apply suitable fertilizers and adjust the soil pH according to tree needs. For microelement deficiency, use foliar sprays and trunk implants of Fe and manganese to provide quick green-up of leaves. Ensure not to apply in the late season because deciduous trees are entering dormancy.
- Maintain a wise watering schedule during the summer to avoid the yellowing of tree leaves. Otherwise, underwatering and overwatering interfere the nutrient absorption and good aeration.
- Plant your landscape trees in ideal sunlight locations where they get 8 hours of morning sunlight daily. For the potted plants, situate them on east, north, and west-facing windows for the best morning sunlight. Avoid placing your potted plant in south-facing windows where the scorching midday sun will burn leaves.
- Spray pesticides and herbicides during cool and dry days when temperatures are around 60 degrees Fahrenheit and low to moderate humidity.
- Do not apply the chemical spray, even neem oil, during temperatures above 85 degrees Fahrenheit and humidity above 90%.
- To avoid fungal and bacterial infections, grow disease-resistant varieties and practice good garden hygiene to remove dry fallen leaves before the fall season. Otherwise, these dead leaves will be a hiding place for insect pests.
- Fertilize the orchard and landscape trees once a month during the spring and summer. It will eliminate the soil’s nutrient deficiencies and assist in rapid new growth.
FAQs on Tree Leaves Turning Yellow
What Deficiency causes the Yellowing of Leaves?
Nitrogen, potassium, and phosphorus deficiency turns the tree leaves yellow. Lack of these nutrients causes the yellowing of leaf edges first, then covering the entire leaf surface.
How do I Fix Yellow Leaves on my Tree?
Once your tree leaves turn yellow, there is nothing much you can do to reverse the chlorosis (the only way is to remove infected foliage). However, there are a few practices you can take to avoid the tree leaves turning yellow, and it includes;
- Avoid improper irrigation
- Prevent overfertilization of synthetic and organic fertilizers.
- Maintain the ideal soil pH levels for microelement availability, such as using elemental sulfur as a soil acidifying agent.
Does Epsom salt help yellow leaves?
Yes, Epsom salt (magnesium sulfate) helps in preventing yellowing leaves. It allows trees with chlorosis and magnesium deficiency by providing sulfates.