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Leaves turn yellow on plants when they lack the green pigment found in chlorophyll. This process, called chlorosis, typically happens gradually, beginning with light green patches on the leaves between the veins and progressing to yellowed and dying leaves. Chlorosis can occur for various reasons, most commonly from nutrient deficiencies or improper watering.
Whether yellow leaves will turn green again depends on the severity of the problem and the underlying cause, such as nutrient deficiencies, drought, wet soggy soil, insect pests, disease, or lack of sunlight. In the initial stages, garden vegetables will ‘green up’ when given the proper nutrients, like tomato or potato plants. However, in advance stages, when the leaves are entirely yellow, the leaves will not turn green again.
Identifying the underlying cause of chlorosis (yellowing leaves) in your plants is the first step to correcting the problem. Find out how to determine why the leaves on your plants turn yellow and what you can do to fix the problem.
What causes yellow leaves on plants?
Plants develop yellow leaves for many reasons. Some of the most commons reasons include poor soil, nutrient deficiencies, improper drainage, improper pH, lack of sunlight, insect pests, and plant diseases. All can affect the plant’s ability to maintain the chlorophyll it needs to keep the leaves a vibrant green, reducing the plant’s ability to perform photosynthesis.
Poor Soil
Nutrient Deficiencies
Nutrient deficiencies are often two-fold. They can occur if the soil lacks the essential nutrients or when the soil pH is too high or too low, making it difficult for the plant to absorb the nutrients it needs to thrive.
Observe for these common traits of nutrient deficiencies if your plant’s leaves turn yellow.
- Nitrogen
A nitrogen deficiency is expected in the early spring when your garden begins to grow. It causes leaves to become pale green with a yellowish tint. Providing your plants with supplemental nitrogen in the spring typically causes the plants to ‘green up’ quickly. You may see the results within a few days.
- Iron
An iron deficiency can occur from a lack of iron in the soil, but it is typically the result of a high soil pH. Plants are most susceptible to an iron deficiency if the soil pH exceeds 7.0, says the University of Maryland Extension.
When plants suffer from an iron deficiency, the outer portions of the leaves turn yellow, but the veins remain green. Correcting the soil pH typically corrects the problem and may revive the yellowed leaves. New growth will be green.
- Sulfur
A sulfur deficiency is less common but can cause the leaves on your plants to turn yellow. The telltale sign of a sulfur deficiency is yellowish-green leaves with elongated stems. The stem may turn woody and spindly.
- Calcium
A calcium deficiency causes new leaves to turn yellow while older leaves remain green. Stems and leaves may appear wilted or droopy. In the case of tomato plants, a calcium deficiency can lead to blossom end rot. In the blossom end rot, the lower leaves may turn yellow while the fruit develops soft black spots on the blossom end of the tomato.
- Zinc
A zinc deficiency affects the leaves of your plants by turning them mottled or with splotchy patches of yellow on the green leaves. These patches may turn brown and die. If treated early, the leaves may revive and turn green again.
- Magnesium
A magnesium deficiency causes the areas between the veins of the leaves to turn yellow. You can treat this easily with Epsom salt (magnesium sulfate) using a spray of 2 tablespoons of magnesium sulfate per gallon of water. When treated with magnesium sulfate, plants with magnesium deficiency generally ‘green up’ in a few days.
Improper Drainage
Poor drainage can lead to wet, soggy soil that will choke out the oxygen to your plant’s roots. When this happens, the roots are not able to absorb nutrients and transport them to the plant’s leaves. As a result, leaves will turn yellow and die. You will likely notice lower leaves turning yellow, but it will progress to the upper leaves if the soil remains soggy.
Likewise, soil that drains too quickly may leave your plants struggling to get the water they need. When the soil is too dry, plants cannot absorb and transport vital nutrients and water for your plants to flourish. This, too, can result in yellowing and dying leaves on your plants. Yellowed leaves from dry soil will gradually turn brown and crispy.
Extremely dry soil is thought to be the root cause of blossom end rot in tomatoes, as the roots are not able to uptake the calcium they need to produce healthy fruits. This can happen even when there is adequate calcium in the soil.
Improper pH
Nutrient deficiencies can occur when there are insufficient nutrients in the soil for your plants to thrive, but that isn’t the only reason. Sometimes nutrient deficiencies arise because the soil pH is too high or too low. When the pH is wrong for your plants, they are not able to uptake the nutrients they need from the soil. It is essential to test the pH of your plant’s soil and adjust it to meet the plant’s needs.
As a rule, plants in the vegetable garden grow best when the soil pH is between 5.8 and 6.5, explains Clemson University Cooperative Extension. Some plants, like blueberries, azaleas, and rhododendrons, prefer acidic soil with a pH between 5.0 and 5.5.
Lack of Sunlight
Most garden vegetables thrive in full sun for 6 to 8 hours a day, while some leafy vegetables like spinach, lettuce, chard, and salad greens can grow in less light. Without enough sunlight, your plants cannot perform photosynthesis and will lack chlorophyll, the pigment that makes the leaves green. Leaves on plants grown in the shade or in areas where they do not receive enough sunlight will turn pale green or yellow.
If lack of sunlight is the cause of yellowing leaves on your plants, check that nearby structures or other large plants do not shade the plants. If your plants are in containers, move them to an area with more light. Likewise, move structures casting shade on your garden, if possible.
Insect Pests
An insect infestation can also cause the leaves of your plants to turn yellow. Exactly which insects are affecting your plants depends on your location and the plant. Examine the plants carefully to determine if insect pests could be the reason for yellowing leaves. Be sure to look along the stems and under the leaves for any signs of chew holes or for busy insects themselves. Insects are typically most active in the morning once the sun has warmed up the area.
If insect pests are the cause of yellowing leaves on your plants, treat them promptly. You can purchase commercial or organic pesticides at your local hardware store or gardening center. Check that the product is appropriate for the specific insect pest in your garden. Insecticides and pesticides list the targeted insect pests on the label.
Always follow the recommended application rate and method. Even organic pesticides can pose a risk to garden pollinators. Apply pesticides when the air is still and there is no breeze.
Diseases
Sometimes yellow leaves on your plants are a sign of disease. Many bacterial, fungal, and viral infections can affect your plants and may turn the leaves yellow. Blight in tomatoes or potatoes begins with brown spots and quickly progresses to yellowed leaves. Other diseases include root rot caused by several fungi that thrive in wet, soggy soil.
If you are unsure whether your plants suffer from plant disease, check with your local extension service for advice. Most provide much information regarding common plant diseases in your area and can help you identify plant diseases.
How do you know if your plants have a nutrient deficiency?
Testing your garden’s soil every three years is recommended to assess the soil’s health. A good soil test will provide you with a host of information, from your soil’s current pH to the nutrient levels in the soil. Many cooperative extension offices offer soil testing for a nominal fee. If your local university does not provide soil testing, contact a soil testing company to test the soil.
A written report will be provided with a thorough assessment of the nutrient levels, pH, and soil composition. It typically includes a list of suggested soil amendments, including the amount and application rate that is right for your garden.
Following the recommendations in the soil analysis report will ensure that your garden soil has the essential ingredients it needs for your plants to flourish.
How do you correct nutrient deficiencies?
Correcting nutrient deficiencies involves supplementing your soil with the needed nutrients or adjusting the pH of the soil. Sometimes, this can mean applying a balanced fertilizer to the garden. Other times it can mean adding trace elements like calcium, zinc, or sulfur.
Because the most common cause of a nutrient deficiency in your plants is improper soil pH, adjusting the soil pH is often the best solution. However, adjusting the soil pH takes time to work its magic.
Lime is typically used to raise the soil pH, but it may take several months to bring the pH up to the proper level. However, you can lower the pH of your soil quickly with an application of sulfur. Both products generally provide instructions on the label to determine the application rate needed for your soil.
Related Questions
Do Yellow Leaves Mean My Plant is Dying?
Not all yellow leaves on plants are a cause for concern. Older, lower leaves on garden plants typically yellow and die off as new leaves are produced. Lower leaves may also turn yellow and drop from the plant because the new foliage shades them. This is normal and does not harm the plant. The older leaves have already served their purpose, and new young leaves will take over the job of performing photosynthesis and making food for the plant.
Some yellow leaves on plants are perfectly normal and do not signify a problem with the plant’s health or growth.
Should you remove yellowed leaves from the plant?
Yellowed leaves that are unsightly can be removed from the plant to improve its appearance as the leaves can no longer perform their task of performing photosynthesis. However, pale yellowish-green leaves may signify a nitrogen or magnesium deficiency and are likely to green up quickly if sprayed with a foliar feeder high in nitrogen or a solution of magnesium sulfate. In this case, removing the leaves would be detrimental to the plant.
Why do the leaves on houseplants turn yellow?
Houseplants face many of the same issues as vegetable plants in the garden. Still, they typically are less likely to suffer from nutrient deficiencies because the potting soil has been specifically designed to provide them with the nutrients they need to thrive. Likewise, houseplant fertilizer provides additional nutrients for the plants.
The most common reasons the leaves on houseplants turn yellow are improper watering, fungal diseases (like root rot), lack of adequate sunlight, and insect pests like thrips, scales, and mites.
Whether the yellow leaves on your plants will turn green again depends on the underlying cause of the yellowed leaves and the severity of the problem. Leaves that have turned completely yellow lack the chlorophyll they need to survive. However, yellowish-green leaves can often be revived if the underlying cause is identified and corrected.
Sources
- https://hgic.clemson.edu/factsheet/changing-the-ph-of-your-soil/
- https://extension.umd.edu/resource/nutrient-deficiency-vegetable-plants
- http://blog.umd.edu/umefruitveg/2021/06/14/plant-detective-why-are-the-leaves-of-my-vegetables-turning-yellow/