Tomatoes are the most favorite plant to grow in a home vegetable garden. The plants are easy to grow and can be grown in containers on a small balcony or in a garden bed in your backyard. While tomato plants are easy to grow, most gardeners encounter one issue very frequently – the yellow leaves on the tomato plants. Since it’s a common problem with several underlying causes, it makes a gardener wonder- why are my tomato plants turning yellow?
Why are your tomato plants turning yellow?
When there are yellow leaves on a tomato plant, it tells you that it is under stress. The stress may be caused by you, by the environment, or by pests and diseases. Still, the plant’s death is imminent unless the source of stress is discovered and corrected.
Go through the table below, asking yourself the following questions until you answer ‘Yes’. Look at the ‘Diagnosis’ column and jump to the corresponding section below. Learn why this situation is causing the yellowing of the tomato plant leaves, how to fix the tomato plant with yellow leaves now, and how to prevent it from re-appearing in the future.
Why are your tomato plants turning yellow?
| # | Diagnosis | |
|---|---|---|
| 1 | Are the yellowing leaves the first set of leaves on the tomato seedling? | Cotyledons |
| 2 | Is the tomato plant transplanted recently? | Transplant shock |
| 3 | Does the soil near the base of the tomato plant consistently stay soggy? | Too much water |
| 4 | Is the soil where the tomato plant is growing feels caky or dry? | Too little water |
| 5 | Is the tomato plant in a shaded area? | Not enough sunlight |
| 6 | Is the soil pH level below 5.5? | Soil is too acidic |
| 7 | Are the top leaves on the tomato plant green, while older leaves turning yellow without any spots? | Nitrogen Deficiency |
| 8 | Does the leaves' yellowing start near the base of the leaves, while leaf veins turn darker? | Iron Deficiency |
| 9 | Do the older leaves on the plant have dark bull’s eye spots with irregular shaped yellow splotches surrounding the darker spots? | Early Blight |
| 10 | Have the yellow leaves developed ‘V’ shaped cuts AND are there roots developed on the stem above the soil level? | Bacterial Wilt |
| 11 | Are there multiple spots on the yellow leaves which have dark brown circles with a tan center? | Septoria Leaf Spot |
| 12 | Are the older, lower leaves on the tomato plant developing yellow blotches with brown veins? | Verticillium Wilt |
| 13 | Did the yellowing of leaves on the tomato plant started on one side of the plant, followed by wilting and browning of the leaves? | Fusarium Wilt |
| 14 | Is Fall season around the corner? | End of the season |
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Here is a helpful guide to grow a healthy Tomato Plant in your garden.
Here are the reasons why Tomato plant leaves could turn yellow:
1. First Set of Leaves (Cotyledons)
The first leaves (the ones nearest to the soil) on tomato seedlings, called cotyledons, are not real leaves. Their primary function is to provide nutrition to the seedlings while true sets of leaves develop and start the photosynthesis process. True leaves are the second set of leaves all garden plants grow. After this set of real leaves develop, the seedling is ready to start making the food itself by using sunlight.
Solution:It’s normal for the first set of leaves to turn yellow and fall off as the plant develops its’ true leaves. If the only yellow leaves on tomato plants are the cotyledons, it’s completely natural. There is nothing to worry about. You can carefully snip those leaves off of the tomato seedling with pointed floral scissors.
2. Transplant Shock
When tomato seedlings are transferred into larger outdoor containers or ground, the plants may go through transplant shock. It is especially true when seedlings are transplanted from a consistently warm indoor location into an outdoor site where the day and night temperatures fluctuate.
After a week or two following the transplant, the once-vibrant green leaves on the plant begin to lighten in color, and you’ll notice the leaves turning yellow on tomato plants. If the newer leaves at the top of the plant are bright green and growing, but the lower leaves are pale yellow, the plant is just going through a short phase of transplant shock.
Treatment:To revive the recently transplanted tomato seedlings from transplant shock, apply a mixture of 1 tbsp of regular granulated sugar diluted in a half-gallon of water. Even though this is not a proven technique, it is popular among home gardeners. Also, keep the transplants hydrated and provide some shade if the day time temperature is too high.
Prevention:Make sure to harden off the seedlings over a 5 to 7 days period. The hardening off process gradually exposes the seedlings to the outdoor environment to handle sunlight and temperature difference without any distress.
3. Over Watering
Tomato plants have a huge thirst and will require a lot of water during the growing season. However, yellow leaves are one of the signs of overwatered tomato plants.
Overwatering causes the soil to become soggy and hinders the flow of oxygen through the soil. The leaves begin to turn yellow due to lack of oxygen, and theoverwatered tomato plants will slowly drown.
Treatment:If a layer of mulch covers the soil near the base of the tomato plant, remove it carefully for a few days. Let the soil exposed to the sunlight and airflow. Trim the access leaves from the plant.
Prevention:If you are manually watering the plant,invest in a good quality water gauge meter to measure the soil moisture before watering. Better yet, install an automatic drip irrigation system along with a weather rain gauge to completely automate the watering. That way, all the vegetable plants in a bed receive a consistent amount of water without worrying about overwatering.
If the tomato plant is growing in a pot or a container, read this post about watering requirements of Tomato plant in a pot.
4. Not Enough Water
A thirsty tomato plant will first wilt, then develop yellow leaves. Wilting is the plant’s first hint that it’s dehydrated. The yellowing of the leaves is telling you that it really needs water. The leaves will first develop a yellow color around the edges. Then it will progress until the entire leaf is yellow and drops off the plant.
Treatment:Water the plant slowly, allowing the soil and roots to absorb the water before it runs off.
Prevention:Water the tomato plant every other day in the morning, making sure not to wet the leaves as much as possible. Use a Water meter to measure the moisture in the soil if needed. Invest in a drip irrigation system.
5. Not Enough Sunlight
Yellow leaves on tomato plants may indicate the plant is not receiving enough sunlight. Even if the plant is in full sunlight, the lower leaves may not be receiving enough light and begin to turn yellow.
The plant will allow some of the lower leaves to turn yellow and die so the rest of the plant and the developing tomatoes can have enough light to reach maturity.
Treatment:Make sure the tomato plant receives at least 8 hours of sunlight. Some cherry tomato plants may survive in around 6 hours of sunlight, but for most large-fruited tomatoes, more than 8 hours of sunlight is ideal. Remove weeds and other plants surrounding the tomato plant so that sunlight can reach the plant’s lower and inner parts.
Prevention:Pick the location for the tomato plant wisely. You can use a Sunlight Meter to measure the hours of sunlight a location receives before planting the tomato plant. If growing in a raised bed, plant them on the Northside of the bed to not shadow the other plants. Locate the raised garden bed away from the shadows of trees and buildings.
6. High pH Level
If tomato plants are planted in the same soil repeatedly, the soil becomes infertile, and the pH level becomes high. When the exhausted soil becomes highly acidic, it will result in yellow leaves on the tomato plant and no tomato production. The tired, infertile soil can’t sustain the plant, and the leaves turn yellow and fall off.
Treatment:Do a soil pH test. If the pH reading is lower than 5.5, the soil is too acidic for the tomato plant to grow. Add Garden Lime to the ground according to the package instruction. Usually, it takes a few days for the lime to breakdown and be available for the plant, so be patient.
Prevention:It is a good habit to test the soil pH at the beginning of each gardening year and amend the soil a few weeks before transplanting the seedlings.
7. Nitrogen Deficiency
Nitrogen is the nutrient needed by plants for above-ground growth. Tomato plants grow very rapidly and must have their roots in nitrogen-rich soil for optimum plant growth and tomato production.
If the soil has a nitrogen deficiency, the older plant leaves will begin to turn pale yellow. The plant’s top leaves will remain green, but the plant will stop growing and producing after the leaves turn yellow.
Treatment:For immediate effect, apply liquid fertilizer with high Nitrogen (N) value. Always follow the direction on the fertilizer package so you don’t burn the plant.
Prevention: Adding Earthworm castings, coffee grounds, and compost boost the Nitrogen level in the soil. Add balanced all-purpose fertilizer (10-10-10) to the soil at the beginning of the season.
It is a good idea to familiarize yourself with the N-P-K requirements of each garden vegetables during it’s life stages. Follow this vegetable garden fertilizer guide for more information.
8. Iron Deficiency
When the soil is not providing the tomato plant with enough iron, the youngest leaves will begin to turn yellow at the base. The yellowing will continue up through the leaf veins, and the base of the leaf will develop a web-like appearance.
The iron-deficient plant will develop pale-yellow leaves that will eventually drop off. The plant will be unproductive after the leaf drop.
Treatment:For a quick fix, apply aLiquid Iron supplement to the tomato plant. It can be sprayed on the foliage if mixed with water or added to the soil. Follow the package direction and repeat the application if required.
Prevention: Adding Rockdust is the best way to prevent the iron (and many other mineral) deficiency in the garden plants. You can also add a powdered or chelated iron supplement in the Spring to amend the soil.
9. Early Blight
A fungus that lives in the soil causes Early blight and attacks tomato plants early in the growing season. It’s a common problem and shows up on the lower, older leaves as irregularly shaped yellow splotches. These yellow splotches will progress into brown spots with a yellow circle (called a halo) around them.
Early blight will continue until the entire leaf is yellow and deformed.
Treatment:If the reason for the yellow leaves on the tomato plant is early blight, immediate actions are required before the entire plant is affected. Remove the affected leaves, throwing them in the garbage (Do not compost these leaves). Cover the base of the plant with mulch. Spray the entire plant, including the underside of the leaves, with Bonide Liquid Copper Fungicide or use Serenade, Actonovate, or any other Copper Fungicide. Another option is to cover the entire plant with a Hydrogen Peroxide mixture (One part Hydrogen Peroxide with five parts of water). This mixture needs to be re-applied every 3-4 days until you see improvement in the plant condition.
Prevention:Follow crop rotation: do not plant the same type of vegetable in the same soil for two years. Mulch the soil with wood chips, straws, or newspapers, so the soil pathogens do not splash back on the plant. Avoid getting the leaves wet while watering.
Prevention is always better than the treatment. Spray the tomato plant with Homemade Neem Oil Spray for plants every 14 days to prevent most of the bacterial and fungal diseases from occurring.
10. Bacterial Wilt
This leaf-yellowing disease is caused by the Ralstonia Solanacearum bacterium. It is typically found in sandy, moist soils near the coastal regions. This bacterial disease infects the tomato plants at planting time. The bacteria enter the plant through the root injury if the root system is injured while transplanting the seedlings. Still, the tomato leaf yellowing and plant wilt will not show up until mid-summer, just before the plant begins to ripen the tomatoes.
The yellow leaves will develop V-shaped cuts. In a few days, the entire plant wilts suddenly.
The tomato plant’s sudden death occurs when the weather is hot, and the soil is moist. In cooler temperatures and drier soil conditions, bacterial wilt symptoms will manifest slower, and plant death will be slower.
Treatment:Unfortunately, there is no cure for the Bacterial wilt once the plant is affected. Remove the plant promptly and dispose of off in the garbage, ensuring the affected leaves don’t touch other plants.
Prevention:To prevent the Bacterial wilt from re-appearing, select the tomato varieties that are Bacterial Wilt resistant. Follow crop rotation and good garden hygiene. Allow ample room between the plants for higher air circulation and prevent the plant leaves from touching each other.
11. Septoria Leaf Spot
Another disease that causes yellow leaves on tomato plants is the Septoria leaf spot. It’s caused by a fungus, Septoria lycopersici, that lives in the soil.
The fungal disease will start as a yellowish circle on the undersides of older leaves located at the bottom of the plant. The rings will have a dark brown margin, a tan center, and a yellow halo around the circle.
The circles will continue to enlarge until the entire leaf is covered, and then it will progress to the plant stem. The yellow leaves will fall off the plant and expose the developing tomato fruits to full sun and cause them to be scalded. The plant will not continue producing, and maturing tomatoes after the leaves fall off.
Treatment:Immediately remove the affected leaves and dispose of in the garbage. There are several products available that can help control the Septoria Leaf spots on a tomato plant. Use Serenade, or Copper Fungicide. For a homemade remedy, hose down the plant with baking soda water (1 tablespoon baking soda mixed in a gallon of water). You can also use Hydrogen Peroxide spray as described in the ‘Early Blight’ section above.
Prevention:Following Crop rotation, increasing the distance between the tomato plants and mulching the soil are the best ways to prevent the Septoria Leaf Spot on tomato plants. Avoid overhead watering and water in the morning hours. Use organic insecticide spray like Neem Oil spray regularly as preventative care.
12. Verticillium Wilt
This is a common soil-born fungus in cool climates where the soil does not warm up until mid-summer. Even though it has wilt in the disease name, the plant does not wilt until the tomato plant has reached maturity, and the tomatoes are almost ready to harvest.
Verticillium wilt shows up as yellow splotches on the lower leaves followed by brown veins extended out from the yellow splotches. After that, dark brown dead spots will appear on the plant leaves.
The yellow spots look similar to those of early blight, but the main difference is verticillium wilt spots do not develop bull’s-eye rings around the splotches. The leaves will eventually fall off the plant, and the plant will be stunted and unproductive after the leaf drop.
Treatment:Unfortunately, there is no chemical-based or organic treatment available for Verticilliumwilt. Remove the infected plant and dispose of in the garbage.
Prevention:Planting Verticillium wilt resistant tomato varieties is the best bet to prevent it. The spores of this fungus stay in the soil for a long time. To eliminate the spores from the ground before the next planting season, Soil solarization should be performed. Follow long term crop rotation to lower the risk of reappearance.
13. Fusarium Wilt
The soil-born fungus, Fusarium oxysporum, is often responsible for yellow leaves on tomato plants. Fusarium wilt will cause the plant to wilt but only on one side. The leaves on the wilted side will begin to turn yellow, and the plant growth will be stunted on the wilted, yellow side.
This plant disease typically starts at the base of a stem and then progresses out the branch, into the leaves, and then into the flowers and tomatoes. Fusarium wilt is common in warm climates where the soil and air temperatures remain above 80 degrees F (29 C).
Treatment:Similar to Verticillium wilt, treating Fusarium wilt is not possible. Prevention is the best key to minimize the risk of Fusarium wilt. Once you identify the cause of the yellowing of the leaves on the tomato plant as Fusarium wilt, promptly remove the plant and put it in the garbage.
Prevention:Follow long term crop rotation and good garden hygiene to minimize the risk of Fusarium wilt in a tomato garden. Select tomato varieties that are resistant to Fusarium wilt. For example, Early Girl, Yellow Pear, Rutgers, Better Bush, etc.
14. End Of the Season
As the gardening season comes to an end, it’s natural for the tomato plants’ leaves to turn yellow. The days get shorter, and the nights get colder. The cool weather signals the plants that fall is near, and their production is complete.
Tomato leaves yellowing and tomato production ceasing are just signs that fall is around the corner. If there are still a few unripe tomatoes on the plant, you can help the plant ripen them with these tips:
Trim off the yellow leaves, remove any tiny tomatoes and new blossoms. Stop watering and feeding the plant at this time too. Doing this will direct all the plant’s energy into ripening the last few tomatoes of the season.
Should I cut yellow leaves off tomato plant?
If the yellow leaves on the tomato plant are due to environmental reasons or a nutritional deficiency, removing some of the plant leaves will help it cope with the situation. The plant can direct the energy in sustaining the rest of the leaves and fruits. If the yellow leaves on the tomato plant are due to bacterial or fungal disease, remove the leaves and discard them in the garbage. Make sure not to compost those leaves. Sterilize the gardening scissors used in removing the yellow, infected leaves before using them again.
Conclusion:
Tomato plants grown in containers or in-ground are subject to the same stress types, except for soil-borne fungus. Small container gardens on an apartment balcony or patio often have better, nutrient-rich soil and produce healthier tomato plants.
Regardless of what size of vegetable garden you have, be observant and watch for the plant stress that often shows up first as yellow leaves on tomato plants.
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